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Activity的XML解析布局

慢行的骑兵
2021-09-20 / 0 评论 / 0 点赞 / 122 阅读 / 3,865 字
  • 该篇笔记记录setContentView的源码执行流程,分为继承自Activity和AppCompatActivity两种情况;
  • sdk版本:28

一.继承Activity

1.setContentView方法

public void setContentView(@LayoutRes int layoutResID) {
    //1.调用window的setContentView
    getWindow().setContentView(layoutResID);
    initWindowDecorActionBar();
}

//Window类(抽象类,唯一的实现类是PhoneWindow)的setContentView方法
public abstract void setContentView(@LayoutRes int layoutResID);

2.PhoneWindow类setContentView

  • 可以把PhoneWindow理解成整个视图的窗体
  • 重要参数1-DecorView mDecor:窗口的顶层视图,它可以包含所有的窗口装饰;
  • 重要参数2-ViewGroup mContentParent:布局容器,这是放置窗口内容的视图。要么是mdecor本省,或者内容所在的mdecor的子级;
public void setContentView(int layoutResID) {
    //mContentParent = null,因为我们当前是窗体初始化
    if (mContentParent == null) {
        //2.初始化顶层布局,分析
        //3.总结:该方法执行了两件事,初始化mDecor和初始化mContentParent
        installDecor();
    } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
        mContentParent.removeAllViews();
    }

    if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
        final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID,
                getContext());
        transitionTo(newScene);
    } else {
        //4.加载我们自己定义的layoutResID,分析
        mLayoutInflater.inflate(layoutResID, mContentParent);
    }
    mContentParent.requestApplyInsets();
    final Callback cb = getCallback();
    if (cb != null && !isDestroyed()) {
        cb.onContentChanged();
    }
    mContentParentExplicitlySet = true;
}

3.installDecor

private void installDecor() {
    mForceDecorInstall = false;
    if (mDecor == null) {
		//2.1.将mDecor初始化,分析
        mDecor = generateDecor(-1);
        mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
        mDecor.setIsRootNamespace(true);
        if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
            mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
        }
    } else {
        mDecor.setWindow(this);
    }
    if (mContentParent == null) {
		//2.2.将mContentParent初始化
        mContentParent = generateLayout(mDecor);

        // Set up decor part of UI to ignore fitsSystemWindows if appropriate.
        mDecor.makeOptionalFitsSystemWindows();

        final DecorContentParent decorContentParent = (DecorContentParent) mDecor.findViewById(
                R.id.decor_content_parent);

        if (decorContentParent != null) {
            mDecorContentParent = decorContentParent;
            mDecorContentParent.setWindowCallback(getCallback());
            if (mDecorContentParent.getTitle() == null) {
                mDecorContentParent.setWindowTitle(mTitle);
            }

            final int localFeatures = getLocalFeatures();
            for (int i = 0; i < FEATURE_MAX; i++) {
                if ((localFeatures & (1 << i)) != 0) {
                    mDecorContentParent.initFeature(i);
                }
            }

            mDecorContentParent.setUiOptions(mUiOptions);

            if ((mResourcesSetFlags & FLAG_RESOURCE_SET_ICON) != 0 ||
                    (mIconRes != 0 && !mDecorContentParent.hasIcon())) {
                mDecorContentParent.setIcon(mIconRes);
            } else if ((mResourcesSetFlags & FLAG_RESOURCE_SET_ICON) == 0 &&
                    mIconRes == 0 && !mDecorContentParent.hasIcon()) {
                mDecorContentParent.setIcon(
                        getContext().getPackageManager().getDefaultActivityIcon());
                mResourcesSetFlags |= FLAG_RESOURCE_SET_ICON_FALLBACK;
            }
            if ((mResourcesSetFlags & FLAG_RESOURCE_SET_LOGO) != 0 ||
                    (mLogoRes != 0 && !mDecorContentParent.hasLogo())) {
                mDecorContentParent.setLogo(mLogoRes);
            }

            // Invalidate if the panel menu hasn't been created before this.
            // Panel menu invalidation is deferred avoiding application onCreateOptionsMenu
            // being called in the middle of onCreate or similar.
            // A pending invalidation will typically be resolved before the posted message
            // would run normally in order to satisfy instance state restoration.
            PanelFeatureState st = getPanelState(FEATURE_OPTIONS_PANEL, false);
            if (!isDestroyed() && (st == null || st.menu == null) && !mIsStartingWindow) {
                invalidatePanelMenu(FEATURE_ACTION_BAR);
            }
        } else {
            mTitleView = findViewById(R.id.title);
            if (mTitleView != null) {
                if ((getLocalFeatures() & (1 << FEATURE_NO_TITLE)) != 0) {
                    final View titleContainer = findViewById(R.id.title_container);
                    if (titleContainer != null) {
                        titleContainer.setVisibility(View.GONE);
                    } else {
                        mTitleView.setVisibility(View.GONE);
                    }
                    mContentParent.setForeground(null);
                } else {
                    mTitleView.setText(mTitle);
                }
            }
        }

        if (mDecor.getBackground() == null && mBackgroundFallbackResource != 0) {
            mDecor.setBackgroundFallback(mBackgroundFallbackResource);
        }

        // Only inflate or create a new TransitionManager if the caller hasn't
        // already set a custom one.
        if (hasFeature(FEATURE_ACTIVITY_TRANSITIONS)) {
            if (mTransitionManager == null) {
                final int transitionRes = getWindowStyle().getResourceId(
                        R.styleable.Window_windowContentTransitionManager,
                        0);
                if (transitionRes != 0) {
                    final TransitionInflater inflater = TransitionInflater.from(getContext());
                    mTransitionManager = inflater.inflateTransitionManager(transitionRes,
                            mContentParent);
                } else {
                    mTransitionManager = new TransitionManager();
                }
            }

            mEnterTransition = getTransition(mEnterTransition, null,
                    R.styleable.Window_windowEnterTransition);
            mReturnTransition = getTransition(mReturnTransition, USE_DEFAULT_TRANSITION,
                    R.styleable.Window_windowReturnTransition);
            mExitTransition = getTransition(mExitTransition, null,
                    R.styleable.Window_windowExitTransition);
            mReenterTransition = getTransition(mReenterTransition, USE_DEFAULT_TRANSITION,
                    R.styleable.Window_windowReenterTransition);
            mSharedElementEnterTransition = getTransition(mSharedElementEnterTransition, null,
                    R.styleable.Window_windowSharedElementEnterTransition);
            mSharedElementReturnTransition = getTransition(mSharedElementReturnTransition,
                    USE_DEFAULT_TRANSITION,
                    R.styleable.Window_windowSharedElementReturnTransition);
            mSharedElementExitTransition = getTransition(mSharedElementExitTransition, null,
                    R.styleable.Window_windowSharedElementExitTransition);
            mSharedElementReenterTransition = getTransition(mSharedElementReenterTransition,
                    USE_DEFAULT_TRANSITION,
                    R.styleable.Window_windowSharedElementReenterTransition);
            if (mAllowEnterTransitionOverlap == null) {
                mAllowEnterTransitionOverlap = getWindowStyle().getBoolean(
                        R.styleable.Window_windowAllowEnterTransitionOverlap, true);
            }
            if (mAllowReturnTransitionOverlap == null) {
                mAllowReturnTransitionOverlap = getWindowStyle().getBoolean(
                        R.styleable.Window_windowAllowReturnTransitionOverlap, true);
            }
            if (mBackgroundFadeDurationMillis < 0) {
                mBackgroundFadeDurationMillis = getWindowStyle().getInteger(
                        R.styleable.Window_windowTransitionBackgroundFadeDuration,
                        DEFAULT_BACKGROUND_FADE_DURATION_MS);
            }
            if (mSharedElementsUseOverlay == null) {
                mSharedElementsUseOverlay = getWindowStyle().getBoolean(
                        R.styleable.Window_windowSharedElementsUseOverlay, true);
            }
        }
    }
}

4.generateDecor

protected DecorView generateDecor(int featureId) {
    Context context;
    if (mUseDecorContext) {
        Context applicationContext = getContext().getApplicationContext();
        if (applicationContext == null) {
            context = getContext();
        } else {
            context = new DecorContext(applicationContext, getContext());
            if (mTheme != -1) {
                context.setTheme(mTheme);
            }
        }
    } else {
        context = getContext();
    }
    //new了一个DecorView,回到2.1,分析2.2
    return new DecorView(context, featureId, this, getAttributes());
}

5.generateLayout

protected ViewGroup generateLayout(DecorView decor) {
    // Apply data from current theme.
	//2.2.1.拿到窗体的样式
    TypedArray a = getWindowStyle();

    //...

    mIsFloating = a.getBoolean(R.styleable.Window_windowIsFloating, false);
    int flagsToUpdate = (FLAG_LAYOUT_IN_SCREEN|FLAG_LAYOUT_INSET_DECOR)
            & (~getForcedWindowFlags());
    if (mIsFloating) {
        setLayout(WRAP_CONTENT, WRAP_CONTENT);
        setFlags(0, flagsToUpdate);
    } else {
        setFlags(FLAG_LAYOUT_IN_SCREEN|FLAG_LAYOUT_INSET_DECOR, flagsToUpdate);
    }

    if (a.getBoolean(R.styleable.Window_windowNoTitle, false)) {
        requestFeature(FEATURE_NO_TITLE);
    } else if (a.getBoolean(R.styleable.Window_windowActionBar, false)) {
        // Don't allow an action bar if there is no title.
        requestFeature(FEATURE_ACTION_BAR);
    }

    if (a.getBoolean(R.styleable.Window_windowActionBarOverlay, false)) {
        requestFeature(FEATURE_ACTION_BAR_OVERLAY);
    }

    if (a.getBoolean(R.styleable.Window_windowActionModeOverlay, false)) {
        requestFeature(FEATURE_ACTION_MODE_OVERLAY);
    }

    if (a.getBoolean(R.styleable.Window_windowSwipeToDismiss, false)) {
        requestFeature(FEATURE_SWIPE_TO_DISMISS);
    }

    if (a.getBoolean(R.styleable.Window_windowFullscreen, false)) {
        setFlags(FLAG_FULLSCREEN, FLAG_FULLSCREEN & (~getForcedWindowFlags()));
    }

    if (a.getBoolean(R.styleable.Window_windowTranslucentStatus,
            false)) {
        setFlags(FLAG_TRANSLUCENT_STATUS, FLAG_TRANSLUCENT_STATUS
                & (~getForcedWindowFlags()));
    }

    if (a.getBoolean(R.styleable.Window_windowTranslucentNavigation,
            false)) {
        setFlags(FLAG_TRANSLUCENT_NAVIGATION, FLAG_TRANSLUCENT_NAVIGATION
                & (~getForcedWindowFlags()));
    }

    if (a.getBoolean(R.styleable.Window_windowOverscan, false)) {
        setFlags(FLAG_LAYOUT_IN_OVERSCAN, FLAG_LAYOUT_IN_OVERSCAN&(~getForcedWindowFlags()));
    }

    if (a.getBoolean(R.styleable.Window_windowShowWallpaper, false)) {
        setFlags(FLAG_SHOW_WALLPAPER, FLAG_SHOW_WALLPAPER&(~getForcedWindowFlags()));
    }

    if (a.getBoolean(R.styleable.Window_windowEnableSplitTouch,
            getContext().getApplicationInfo().targetSdkVersion
                    >= android.os.Build.VERSION_CODES.HONEYCOMB)) {
        setFlags(FLAG_SPLIT_TOUCH, FLAG_SPLIT_TOUCH&(~getForcedWindowFlags()));
    }

    a.getValue(R.styleable.Window_windowMinWidthMajor, mMinWidthMajor);
    a.getValue(R.styleable.Window_windowMinWidthMinor, mMinWidthMinor);
    if (DEBUG) Log.d(TAG, "Min width minor: " + mMinWidthMinor.coerceToString()
            + ", major: " + mMinWidthMajor.coerceToString());
    if (a.hasValue(R.styleable.Window_windowFixedWidthMajor)) {
        if (mFixedWidthMajor == null) mFixedWidthMajor = new TypedValue();
        a.getValue(R.styleable.Window_windowFixedWidthMajor,
                mFixedWidthMajor);
    }
    if (a.hasValue(R.styleable.Window_windowFixedWidthMinor)) {
        if (mFixedWidthMinor == null) mFixedWidthMinor = new TypedValue();
        a.getValue(R.styleable.Window_windowFixedWidthMinor,
                mFixedWidthMinor);
    }
    if (a.hasValue(R.styleable.Window_windowFixedHeightMajor)) {
        if (mFixedHeightMajor == null) mFixedHeightMajor = new TypedValue();
        a.getValue(R.styleable.Window_windowFixedHeightMajor,
                mFixedHeightMajor);
    }
    if (a.hasValue(R.styleable.Window_windowFixedHeightMinor)) {
        if (mFixedHeightMinor == null) mFixedHeightMinor = new TypedValue();
        a.getValue(R.styleable.Window_windowFixedHeightMinor,
                mFixedHeightMinor);
    }
    if (a.getBoolean(R.styleable.Window_windowContentTransitions, false)) {
        requestFeature(FEATURE_CONTENT_TRANSITIONS);
    }
    if (a.getBoolean(R.styleable.Window_windowActivityTransitions, false)) {
        requestFeature(FEATURE_ACTIVITY_TRANSITIONS);
    }

    mIsTranslucent = a.getBoolean(R.styleable.Window_windowIsTranslucent, false);

    final Context context = getContext();
    final int targetSdk = context.getApplicationInfo().targetSdkVersion;
    final boolean targetPreHoneycomb = targetSdk < android.os.Build.VERSION_CODES.HONEYCOMB;
    final boolean targetPreIcs = targetSdk < android.os.Build.VERSION_CODES.ICE_CREAM_SANDWICH;
    final boolean targetPreL = targetSdk < android.os.Build.VERSION_CODES.LOLLIPOP;
    final boolean targetHcNeedsOptions = context.getResources().getBoolean(
            R.bool.target_honeycomb_needs_options_menu);
    final boolean noActionBar = !hasFeature(FEATURE_ACTION_BAR) || hasFeature(FEATURE_NO_TITLE);

    if (targetPreHoneycomb || (targetPreIcs && targetHcNeedsOptions && noActionBar)) {
        setNeedsMenuKey(WindowManager.LayoutParams.NEEDS_MENU_SET_TRUE);
    } else {
        setNeedsMenuKey(WindowManager.LayoutParams.NEEDS_MENU_SET_FALSE);
    }

    if (!mForcedStatusBarColor) {
        mStatusBarColor = a.getColor(R.styleable.Window_statusBarColor, 0xFF000000);
    }
    if (!mForcedNavigationBarColor) {
        mNavigationBarColor = a.getColor(R.styleable.Window_navigationBarColor, 0xFF000000);
        mNavigationBarDividerColor = a.getColor(R.styleable.Window_navigationBarDividerColor,
                0x00000000);
    }

    WindowManager.LayoutParams params = getAttributes();

    // Non-floating windows on high end devices must put up decor beneath the system bars and
    // therefore must know about visibility changes of those.
    if (!mIsFloating) {
        if (!targetPreL && a.getBoolean(
                R.styleable.Window_windowDrawsSystemBarBackgrounds,
                false)) {
            setFlags(FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS,
                    FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS & ~getForcedWindowFlags());
        }
        if (mDecor.mForceWindowDrawsStatusBarBackground) {
            params.privateFlags |= PRIVATE_FLAG_FORCE_DRAW_STATUS_BAR_BACKGROUND;
        }
    }
    if (a.getBoolean(R.styleable.Window_windowLightStatusBar, false)) {
        decor.setSystemUiVisibility(
                decor.getSystemUiVisibility() | View.SYSTEM_UI_FLAG_LIGHT_STATUS_BAR);
    }
    if (a.getBoolean(R.styleable.Window_windowLightNavigationBar, false)) {
        decor.setSystemUiVisibility(
                decor.getSystemUiVisibility() | View.SYSTEM_UI_FLAG_LIGHT_NAVIGATION_BAR);
    }
    if (a.hasValue(R.styleable.Window_windowLayoutInDisplayCutoutMode)) {
        int mode = a.getInt(R.styleable.Window_windowLayoutInDisplayCutoutMode, -1);
        if (mode < LAYOUT_IN_DISPLAY_CUTOUT_MODE_DEFAULT
                || mode > LAYOUT_IN_DISPLAY_CUTOUT_MODE_NEVER) {
            throw new UnsupportedOperationException("Unknown windowLayoutInDisplayCutoutMode: "
                    + a.getString(R.styleable.Window_windowLayoutInDisplayCutoutMode));
        }
        params.layoutInDisplayCutoutMode = mode;
    }

    if (mAlwaysReadCloseOnTouchAttr || getContext().getApplicationInfo().targetSdkVersion
            >= android.os.Build.VERSION_CODES.HONEYCOMB) {
        if (a.getBoolean(
                R.styleable.Window_windowCloseOnTouchOutside,
                false)) {
            setCloseOnTouchOutsideIfNotSet(true);
        }
    }

    if (!hasSoftInputMode()) {
        params.softInputMode = a.getInt(
                R.styleable.Window_windowSoftInputMode,
                params.softInputMode);
    }

    if (a.getBoolean(R.styleable.Window_backgroundDimEnabled,
            mIsFloating)) {
        /* All dialogs should have the window dimmed */
        if ((getForcedWindowFlags()&WindowManager.LayoutParams.FLAG_DIM_BEHIND) == 0) {
            params.flags |= WindowManager.LayoutParams.FLAG_DIM_BEHIND;
        }
        if (!haveDimAmount()) {
            params.dimAmount = a.getFloat(
                    android.R.styleable.Window_backgroundDimAmount, 0.5f);
        }
    }

    if (params.windowAnimations == 0) {
        params.windowAnimations = a.getResourceId(
                R.styleable.Window_windowAnimationStyle, 0);
    }

    // The rest are only done if this window is not embedded; otherwise,
    // the values are inherited from our container.
    if (getContainer() == null) {
        if (mBackgroundDrawable == null) {
            if (mBackgroundResource == 0) {
                mBackgroundResource = a.getResourceId(
                        R.styleable.Window_windowBackground, 0);
            }
            if (mFrameResource == 0) {
                mFrameResource = a.getResourceId(R.styleable.Window_windowFrame, 0);
            }
            mBackgroundFallbackResource = a.getResourceId(
                    R.styleable.Window_windowBackgroundFallback, 0);
            if (false) {
                System.out.println("Background: "
                        + Integer.toHexString(mBackgroundResource) + " Frame: "
                        + Integer.toHexString(mFrameResource));
            }
        }
        if (mLoadElevation) {
            mElevation = a.getDimension(R.styleable.Window_windowElevation, 0);
        }
        mClipToOutline = a.getBoolean(R.styleable.Window_windowClipToOutline, false);
        mTextColor = a.getColor(R.styleable.Window_textColor, Color.TRANSPARENT);
    }
	
	//2.2.2.上方是主题的判断

    // Inflate the window decor.
	//2.2.3.给窗体进行装饰
	
    int layoutResource;		//资源id,根据主题加载不同xml文件
    int features = getLocalFeatures();
    // System.out.println("Features: 0x" + Integer.toHexString(features));
    if ((features & (1 << FEATURE_SWIPE_TO_DISMISS)) != 0) {
        layoutResource = R.layout.screen_swipe_dismiss;
        setCloseOnSwipeEnabled(true);
    } else if ((features & ((1 << FEATURE_LEFT_ICON) | (1 << FEATURE_RIGHT_ICON))) != 0) {
        if (mIsFloating) {
            TypedValue res = new TypedValue();
            getContext().getTheme().resolveAttribute(
                    R.attr.dialogTitleIconsDecorLayout, res, true);
            layoutResource = res.resourceId;
        } else {
            layoutResource = R.layout.screen_title_icons;
        }
        // XXX Remove this once action bar supports these features.
        removeFeature(FEATURE_ACTION_BAR);
        // System.out.println("Title Icons!");
    } else if ((features & ((1 << FEATURE_PROGRESS) | (1 << FEATURE_INDETERMINATE_PROGRESS))) != 0
            && (features & (1 << FEATURE_ACTION_BAR)) == 0) {
        // Special case for a window with only a progress bar (and title).
        // XXX Need to have a no-title version of embedded windows.
        layoutResource = R.layout.screen_progress;
        // System.out.println("Progress!");
    } else if ((features & (1 << FEATURE_CUSTOM_TITLE)) != 0) {
        // Special case for a window with a custom title.
        // If the window is floating, we need a dialog layout
        if (mIsFloating) {
            TypedValue res = new TypedValue();
            getContext().getTheme().resolveAttribute(
                    R.attr.dialogCustomTitleDecorLayout, res, true);
            layoutResource = res.resourceId;
        } else {
            layoutResource = R.layout.screen_custom_title;
        }
        // XXX Remove this once action bar supports these features.
        removeFeature(FEATURE_ACTION_BAR);
    } else if ((features & (1 << FEATURE_NO_TITLE)) == 0) {
        // If no other features and not embedded, only need a title.
        // If the window is floating, we need a dialog layout
        if (mIsFloating) {
            TypedValue res = new TypedValue();
            getContext().getTheme().resolveAttribute(
                    R.attr.dialogTitleDecorLayout, res, true);
            layoutResource = res.resourceId;
        } else if ((features & (1 << FEATURE_ACTION_BAR)) != 0) {
            layoutResource = a.getResourceId(
                    R.styleable.Window_windowActionBarFullscreenDecorLayout,
                    R.layout.screen_action_bar);
        } else {
            layoutResource = R.layout.screen_title;
        }
        // System.out.println("Title!");
    } else if ((features & (1 << FEATURE_ACTION_MODE_OVERLAY)) != 0) {
        layoutResource = R.layout.screen_simple_overlay_action_mode;
    } else {
        // Embedded, so no decoration is needed.
        layoutResource = R.layout.screen_simple;
        // System.out.println("Simple!");
    }

    mDecor.startChanging();
    //2.2.4.分析onResourcesLoaded
    //将家中到的基础布局添加到mDecor里面
    mDecor.onResourcesLoaded(mLayoutInflater, layoutResource);

    //2.2.5.通过系统的content的资源ID进行实例化这个控件
    ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
    if (contentParent == null) {
        throw new RuntimeException("Window couldn't find content container view");
    }

    if ((features & (1 << FEATURE_INDETERMINATE_PROGRESS)) != 0) {
        ProgressBar progress = getCircularProgressBar(false);
        if (progress != null) {
            progress.setIndeterminate(true);
        }
    }

    if ((features & (1 << FEATURE_SWIPE_TO_DISMISS)) != 0) {
        registerSwipeCallbacks(contentParent);
    }

    // Remaining setup -- of background and title -- that only applies
    // to top-level windows.
    if (getContainer() == null) {
        final Drawable background;
        if (mBackgroundResource != 0) {
            background = getContext().getDrawable(mBackgroundResource);
        } else {
            background = mBackgroundDrawable;
        }
        mDecor.setWindowBackground(background);

        final Drawable frame;
        if (mFrameResource != 0) {
            frame = getContext().getDrawable(mFrameResource);
        } else {
            frame = null;
        }
        mDecor.setWindowFrame(frame);

        mDecor.setElevation(mElevation);
        mDecor.setClipToOutline(mClipToOutline);

        if (mTitle != null) {
            setTitle(mTitle);
        }

        if (mTitleColor == 0) {
            mTitleColor = mTextColor;
        }
        setTitleColor(mTitleColor);
    }

    mDecor.finishChanging();
	//2.2.6.将contentParent返回回去,实际上contentParent是mDecor的一个子view
    //返回到generateLayout调用的地方继续分析
    return contentParent;
}

6.分析screen_simple.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    android:orientation="vertical">
    <ViewStub android:id="@+id/action_mode_bar_stub"
              android:inflatedId="@+id/action_mode_bar"
              android:layout="@layout/action_mode_bar"
              android:layout_width="match_parent"
              android:layout_height="wrap_content"
              android:theme="?attr/actionBarTheme" />
    <FrameLayout
         android:id="@android:id/content"
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         android:foregroundInsidePadding="false"
         android:foregroundGravity="fill_horizontal|top"
         android:foreground="?android:attr/windowContentOverlay" />
</LinearLayout>

7.分析onResourcesLoaded

void onResourcesLoaded(LayoutInflater inflater, int layoutResource) {
    if (mBackdropFrameRenderer != null) {
        loadBackgroundDrawablesIfNeeded();
        mBackdropFrameRenderer.onResourcesLoaded(
                this, mResizingBackgroundDrawable, mCaptionBackgroundDrawable,
                mUserCaptionBackgroundDrawable, getCurrentColor(mStatusColorViewState),
                getCurrentColor(mNavigationColorViewState));
    }

    mDecorCaptionView = createDecorCaptionView(inflater);
	//把传进来的layoutResource布局进行解析并渲染
    final View root = inflater.inflate(layoutResource, null);
    if (mDecorCaptionView != null) {
        if (mDecorCaptionView.getParent() == null) {
            addView(mDecorCaptionView,
                    new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
        }
        mDecorCaptionView.addView(root,
                new ViewGroup.MarginLayoutParams(MATCH_PARENT, MATCH_PARENT));
    } else {

        // Put it below the color views.
        addView(root, 0, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
    }
    mContentRoot = (ViewGroup) root;
    initializeElevation();
}

8.mLayoutInflater.inflate(layoutResID, mContentParent)

public View inflate(@LayoutRes int resource, @Nullable ViewGroup root) {
    return inflate(resource, root, root != null);
}

public View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot) {
    final Resources res = getContext().getResources();
    if (DEBUG) {
        Log.d(TAG, "INFLATING from resource: \"" + res.getResourceName(resource) + "\" ("
                + Integer.toHexString(resource) + ")");
    }

	//5.解析xml文件
    final XmlResourceParser parser = res.getLayout(resource);
    try {
		//6.调用inflate-跟踪root
        return inflate(parser, root, attachToRoot);
    } finally {
        parser.close();
    }
}

9.inflate(parser, root, attachToRoot)

public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {
    synchronized (mConstructorArgs) {
        Trace.traceBegin(Trace.TRACE_TAG_VIEW, "inflate");

        final Context inflaterContext = mContext;
        final AttributeSet attrs = Xml.asAttributeSet(parser);
        Context lastContext = (Context) mConstructorArgs[0];
        mConstructorArgs[0] = inflaterContext;
        View result = root;

        try {
            // Look for the root node.
            int type;
            while ((type = parser.next()) != XmlPullParser.START_TAG &&
                    type != XmlPullParser.END_DOCUMENT) {
                // Empty
            }

            if (type != XmlPullParser.START_TAG) {
                throw new InflateException(parser.getPositionDescription()
                        + ": No start tag found!");
            }

            final String name = parser.getName();

            if (DEBUG) {
                System.out.println("**************************");
                System.out.println("Creating root view: "
                        + name);
                System.out.println("**************************");
            }

            if (TAG_MERGE.equals(name)) {
                if (root == null || !attachToRoot) {
                    throw new InflateException("<merge /> can be used only with a valid "
                            + "ViewGroup root and attachToRoot=true");
                }

                rInflate(parser, root, inflaterContext, attrs, false);
            } else {
                // Temp is the root view that was found in the xml
                final View temp = createViewFromTag(root, name, inflaterContext, attrs);

                ViewGroup.LayoutParams params = null;

                if (root != null) {
                    if (DEBUG) {
                        System.out.println("Creating params from root: " +
                                root);
                    }
                    // Create layout params that match root, if supplied
                    params = root.generateLayoutParams(attrs);
                    if (!attachToRoot) {
                        // Set the layout params for temp if we are not
                        // attaching. (If we are, we use addView, below)
                        temp.setLayoutParams(params);
                    }
                }

                if (DEBUG) {
                    System.out.println("-----> start inflating children");
                }

                // Inflate all children under temp against its context.
                rInflateChildren(parser, temp, attrs, true);

                if (DEBUG) {
                    System.out.println("-----> done inflating children");
                }

                // We are supposed to attach all the views we found (int temp)
                // to root. Do that now.
                if (root != null && attachToRoot) {
                    //把我们自定义的布局解析完毕之后,添加到mContentParent中
                    root.addView(temp, params);
                }

                // Decide whether to return the root that was passed in or the
                // top view found in xml.
                if (root == null || !attachToRoot) {
                    result = temp;
                }
            }

        } 
        //...

        return result;
    }
}

二.继承自AppCompatActivity

public void setContentView(@LayoutRes int layoutResID) {
    //1.调用AppCompatDelegate(抽象类,实现类是AppCompatDelegateImpl)的setContentView方法
    getDelegate().setContentView(layoutResID);
}

2.AppCompatDelegateImpl的setContentView

public void setContentView(View v) {
    //初始化根布局
    ensureSubDecor();
    ViewGroup contentParent = mSubDecor.findViewById(android.R.id.content);
    contentParent.removeAllViews();
    //将我们自己传递进来的xml布局添加到contentParent中
    LayoutInflater.from(mContext).inflate(resId, contentParent);
    mAppCompatWindowCallback.getWrapped().onContentChanged();
}

3.ensureSubDecor

private void ensureSubDecor() {
    if (!mSubDecorInstalled) {
        //可以将mSubDecor理解为根布局
        mSubDecor = createSubDecor();

        // If a title was set before we installed the decor, propagate it now
        CharSequence title = getTitle();
        if (!TextUtils.isEmpty(title)) {
            if (mDecorContentParent != null) {
                mDecorContentParent.setWindowTitle(title);
            } else if (peekSupportActionBar() != null) {
                peekSupportActionBar().setWindowTitle(title);
            } else if (mTitleView != null) {
                mTitleView.setText(title);
            }
        }

        applyFixedSizeWindow();

        onSubDecorInstalled(mSubDecor);

        mSubDecorInstalled = true;

        PanelFeatureState st = getPanelState(FEATURE_OPTIONS_PANEL, false);
        if (!mIsDestroyed && (st == null || st.menu == null)) {
            invalidatePanelMenu(FEATURE_SUPPORT_ACTION_BAR);
        }
    }
}

4.createSubDecor

private ViewGroup createSubDecor() {
    //判断样式
    TypedArray a = mContext.obtainStyledAttributes(R.styleable.AppCompatTheme);

    if (!a.hasValue(R.styleable.AppCompatTheme_windowActionBar)) {
        a.recycle();
        throw new IllegalStateException(
                "You need to use a Theme.AppCompat theme (or descendant) with this activity.");
    }

    if (a.getBoolean(R.styleable.AppCompatTheme_windowNoTitle, false)) {
        requestWindowFeature(Window.FEATURE_NO_TITLE);
    } else if (a.getBoolean(R.styleable.AppCompatTheme_windowActionBar, false)) {
        // Don't allow an action bar if there is no title.
        requestWindowFeature(FEATURE_SUPPORT_ACTION_BAR);
    }
    if (a.getBoolean(R.styleable.AppCompatTheme_windowActionBarOverlay, false)) {
        requestWindowFeature(FEATURE_SUPPORT_ACTION_BAR_OVERLAY);
    }
    if (a.getBoolean(R.styleable.AppCompatTheme_windowActionModeOverlay, false)) {
        requestWindowFeature(FEATURE_ACTION_MODE_OVERLAY);
    }
    mIsFloating = a.getBoolean(R.styleable.AppCompatTheme_android_windowIsFloating, false);
    a.recycle();

    // Now let's make sure that the Window has installed its decor by retrieving it
    ensureWindow();
    mWindow.getDecorView();

    final LayoutInflater inflater = LayoutInflater.from(mContext);
    ViewGroup subDecor = null;


    if (!mWindowNoTitle) {
        if (mIsFloating) {
            // If we're floating, inflate the dialog title decor
            //根据主题不同来加载不同的xml,把加载的xml给subDecor
            subDecor = (ViewGroup) inflater.inflate(
                    R.layout.abc_dialog_title_material, null);

            // Floating windows can never have an action bar, reset the flags
            mHasActionBar = mOverlayActionBar = false;
        } else if (mHasActionBar) {
            /**
             * This needs some explanation. As we can not use the android:theme attribute
             * pre-L, we emulate it by manually creating a LayoutInflater using a
             * ContextThemeWrapper pointing to actionBarTheme.
             */
            TypedValue outValue = new TypedValue();
            mContext.getTheme().resolveAttribute(R.attr.actionBarTheme, outValue, true);

            Context themedContext;
            if (outValue.resourceId != 0) {
                themedContext = new ContextThemeWrapper(mContext, outValue.resourceId);
            } else {
                themedContext = mContext;
            }

            // Now inflate the view using the themed context and set it as the content view
            subDecor = (ViewGroup) LayoutInflater.from(themedContext)
                    .inflate(R.layout.abc_screen_toolbar, null);

            mDecorContentParent = (DecorContentParent) subDecor
                    .findViewById(R.id.decor_content_parent);
            mDecorContentParent.setWindowCallback(getWindowCallback());

            /**
             * Propagate features to DecorContentParent
             */
            if (mOverlayActionBar) {
                mDecorContentParent.initFeature(FEATURE_SUPPORT_ACTION_BAR_OVERLAY);
            }
            if (mFeatureProgress) {
                mDecorContentParent.initFeature(Window.FEATURE_PROGRESS);
            }
            if (mFeatureIndeterminateProgress) {
                mDecorContentParent.initFeature(Window.FEATURE_INDETERMINATE_PROGRESS);
            }
        }
    } else {
        if (mOverlayActionMode) {
            subDecor = (ViewGroup) inflater.inflate(
                    R.layout.abc_screen_simple_overlay_action_mode, null);
        } else {
            subDecor = (ViewGroup) inflater.inflate(R.layout.abc_screen_simple, null);
        }
    }

    if (subDecor == null) {
        throw new IllegalArgumentException(
                "AppCompat does not support the current theme features: { "
                        + "windowActionBar: " + mHasActionBar
                        + ", windowActionBarOverlay: "+ mOverlayActionBar
                        + ", android:windowIsFloating: " + mIsFloating
                        + ", windowActionModeOverlay: " + mOverlayActionMode
                        + ", windowNoTitle: " + mWindowNoTitle
                        + " }");
    }

    if (Build.VERSION.SDK_INT >= 21) {
        // If we're running on L or above, we can rely on ViewCompat's
        // setOnApplyWindowInsetsListener
        ViewCompat.setOnApplyWindowInsetsListener(subDecor, new OnApplyWindowInsetsListener() {
                    @Override
                    public WindowInsetsCompat onApplyWindowInsets(View v,
                            WindowInsetsCompat insets) {
                        final int top = insets.getSystemWindowInsetTop();
                        final int newTop = updateStatusGuard(insets, null);

                        if (top != newTop) {
                            insets = insets.replaceSystemWindowInsets(
                                    insets.getSystemWindowInsetLeft(),
                                    newTop,
                                    insets.getSystemWindowInsetRight(),
                                    insets.getSystemWindowInsetBottom());
                        }

                        // Now apply the insets on our view
                        return ViewCompat.onApplyWindowInsets(v, insets);
                    }
                });
    } else if (subDecor instanceof FitWindowsViewGroup) {
        // Else, we need to use our own FitWindowsViewGroup handling
        ((FitWindowsViewGroup) subDecor).setOnFitSystemWindowsListener(
                new FitWindowsViewGroup.OnFitSystemWindowsListener() {
                    @Override
                    public void onFitSystemWindows(Rect insets) {
                        insets.top = updateStatusGuard(null, insets);
                    }
                });
    }

    if (mDecorContentParent == null) {
        mTitleView = (TextView) subDecor.findViewById(R.id.title);
    }

    // Make the decor optionally fit system windows, like the window's decor
    ViewUtils.makeOptionalFitsSystemWindows(subDecor);

    //得到一个控件
    final ContentFrameLayout contentView = (ContentFrameLayout) subDecor.findViewById(
            R.id.action_bar_activity_content);

    //创建一个windowContentView
    final ViewGroup windowContentView = (ViewGroup) mWindow.findViewById(android.R.id.content);
    if (windowContentView != null) {
        // There might be Views already added to the Window's content view so we need to
        // migrate them to our content view
        while (windowContentView.getChildCount() > 0) {
            final View child = windowContentView.getChildAt(0);
            windowContentView.removeViewAt(0);
            contentView.addView(child);
        }

        // Change our content FrameLayout to use the android.R.id.content id.
        // Useful for fragments.
        //将windowContentView的id设置为-1,然后将contentView的id设置为android.R.id.content
        windowContentView.setId(View.NO_ID);
        contentView.setId(android.R.id.content);

        // The decorContent may have a foreground drawable set (windowContentOverlay).
        // Remove this as we handle it ourselves
        if (windowContentView instanceof FrameLayout) {
            ((FrameLayout) windowContentView).setForeground(null);
        }
    }

    // Now set the Window's content view with the decor
    mWindow.setContentView(subDecor);

    contentView.setAttachListener(new ContentFrameLayout.OnAttachListener() {
        @Override
        public void onAttachedFromWindow() {}

        @Override
        public void onDetachedFromWindow() {
            dismissPopups();
        }
    });

    return subDecor;
}

三.流程图

02.Activity的XML解析布局

四.总结

  • 解析XML文件
    • 先初始化基础布局(根布局);
    • 然后将自己传进来的XML解析添加进入;
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