Android setContentView源码解析

/**
 * Base class for activities that use the
 * <a href="{@docRoot}tools/extras/support-library.html">support library</a> action bar features.
 *
 * <p>You can add an {@link android.support.v7.app.ActionBar} to your activity when running on API level 7 or higher
 * by extending this class for your activity and setting the activity theme to
 * {@link android.support.v7.appcompat.R.style#Theme_AppCompat Theme.AppCompat} or a similar theme.
 *
 * <div class="special reference">
 * <h3>Developer Guides</h3>
 *
 * <p>For information about how to use the action bar, including how to add action items, navigation
 * modes and more, read the <a href="{@docRoot}guide/topics/ui/actionbar.html">Action
 * Bar</a> API guide.</p>
 * </div>
 */

    @Override
    public void setContentView(@LayoutRes int layoutResID) {
        getDelegate().setContentView(layoutResID);
    }

    public AppCompatDelegate getDelegate() {
        if (mDelegate == null) {
            mDelegate = AppCompatDelegate.create(this, this);
        }
        return mDelegate;
    }
    // 真正到了这里
    private static AppCompatDelegate create(Context context, Window window,
            AppCompatCallback callback) {
        if (Build.VERSION.SDK_INT >= 24) {
            return new AppCompatDelegateImplN(context, window, callback);
        } else if (Build.VERSION.SDK_INT >= 23) {
            return new AppCompatDelegateImplV23(context, window, callback);
        } else if (Build.VERSION.SDK_INT >= 14) {
            return new AppCompatDelegateImplV14(context, window, callback);
        } else if (Build.VERSION.SDK_INT >= 11) {
            return new AppCompatDelegateImplV11(context, window, callback);
        } else {
            return new AppCompatDelegateImplV9(context, window, callback);
        }
    }

    @Override
    public void setContentView(View v) {
        ensureSubDecor();
        ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content);
        contentParent.removeAllViews();
        contentParent.addView(v);
        mOriginalWindowCallback.onContentChanged();
    }

    // 此处可以看出SubDecor是一个ViewGroup
    private ViewGroup createSubDecor() {
        TypedArray a = mContext.obtainStyledAttributes(R.styleable.AppCompatTheme);
        if (!a.hasValue(R.styleable.AppCompatTheme_windowActionBar)) {
            a.recycle();
            // 这个错大家可能遇到过，当使用了AppCompatActivity但是没有设置一个Theme.AppCompat的主题，则会报这个Exception。
            throw new IllegalStateException(
                    "You need to use a Theme.AppCompat theme (or descendant) with this activity.");
        }
        // 接下来就到了设置一些Window属性的地方，下面会再说
        if (a.getBoolean(R.styleable.AppCompatTheme_windowNoTitle, false)) {
            requestWindowFeature(Window.FEATURE_NO_TITLE);// 设置无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
        mWindow.getDecorView();// 就是创建DecorView
        final LayoutInflater inflater = LayoutInflater.from(mContext);
        ViewGroup subDecor = null;
        // 根据标记来决定inflate哪个layout
        if (!mWindowNoTitle) {
            if (mIsFloating) {
                // If we're floating, inflate the dialog title decor
                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) {
                ......
            }
        } else {
        }
        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 (mDecorContentParent == null) {
            mTitleView = (TextView) subDecor.findViewById(R.id.title);
        }
        // Make the decor optionally fit system windows, like the window's decor
        ViewUtils.makeOptionalFitsSystemWindows(subDecor);
        final ContentFrameLayout contentView = (ContentFrameLayout) subDecor.findViewById(
                R.id.action_bar_activity_content);
        // 获取PhoneWindow中的content布局对象
        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.
            windowContentView.setId(View.NO_ID);
            // 将contentView的id设置为android.R.id.content
            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;
    }

    @Override
    public boolean requestWindowFeature(int featureId) {
        ......
        switch (featureId) {
            case FEATURE_SUPPORT_ACTION_BAR:
                throwFeatureRequestIfSubDecorInstalled();
                mHasActionBar = true;// 仅仅是对变量赋值
                return true;
        ......
        }
        return mWindow.requestFeature(featureId);
    }
    // 这个又解释了一个原因，我们如果在setContentView之后再次去设置requestWindowFeature，会抛出Exception。
    private void throwFeatureRequestIfSubDecorInstalled() {
        if (mSubDecorInstalled) {
            throw new AndroidRuntimeException(
                    "Window feature must be requested before adding content");
        }
    }

    private void installDecor() {
        mForceDecorInstall = false;
        if (mDecor == null) {
            mDecor = generateDecor(-1);// 重点
            mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
            mDecor.setIsRootNamespace(true);
            if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
                mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
            }
        } else {
            mDecor.setWindow(this);
        }
        if (mContentParent == null) {
            mContentParent = generateLayout(mDecor);// 重点
            ......
        }
    }    
    // generateDecor最后只是new了一个DecorView
    protected DecorView generateDecor(int featureId) {
        ......
        return new DecorView(context, featureId, this, getAttributes());
    }
    // 看一下DecorView的定义可以看出它是一个FrameLayout
    /** @hide */
    public class DecorView extends FrameLayout implements RootViewSurfaceTaker, WindowCallbacks {
    }

    void onResourcesLoaded(LayoutInflater inflater, int layoutResource) {
        mStackId = getStackId();
        if (mBackdropFrameRenderer != null) {
            loadBackgroundDrawablesIfNeeded();
            mBackdropFrameRenderer.onResourcesLoaded(
                    this, mResizingBackgroundDrawable, mCaptionBackgroundDrawable,
                    mUserCaptionBackgroundDrawable, getCurrentColor(mStatusColorViewState),
                    getCurrentColor(mNavigationColorViewState));
        }
        mDecorCaptionView = createDecorCaptionView(inflater);
        final View root = inflater.inflate(layoutResource, null);// inflate出View
        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();
    }

        // SubDecor中也一定有这个id
        final ContentFrameLayout contentView = (ContentFrameLayout) subDecor.findViewById(
                R.id.action_bar_activity_content);
        // 这里的content就是是PhoneWindow中的content，上面提到过
        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
            // 合并PhoneWindow中的view到SubDecor中的content中
            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.
            // id在这里发生了变化
            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);
            }
        }

    @Override
    public void setContentView(View view, ViewGroup.LayoutParams params) {
        // Note: FEATURE_CONTENT_TRANSITIONS may be set in the process of installing the window
        // decor, when theme attributes and the like are crystalized. Do not check the feature
        // before this happens.
        // mContentParent是不是看起来有点熟悉呢？generateLayout函数的返回值就是它
        if (mContentParent == null) {
            installDecor();
        } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
            mContentParent.removeAllViews();
        }
        if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
            view.setLayoutParams(params);
            final Scene newScene = new Scene(mContentParent, view);
            transitionTo(newScene);// 有过渡动画的情况下用到了Scene
        } else {
            // 备注，mContentParent之前是@android:id/content，现在是View.NO_ID；
            // 现在的@android:id/content是SubDecor中的action_bar_activity_content
            mContentParent.addView(view, params);
        }
        mContentParent.requestApplyInsets();
        final Callback cb = getCallback();
        if (cb != null && !isDestroyed()) {
            cb.onContentChanged();
        }
        mContentParentExplicitlySet = true;
    }

    @Override
    public void setContentView(int resId) {
        ensureSubDecor();
        ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content);
        contentParent.removeAllViews();
        LayoutInflater.from(mContext).inflate(resId, contentParent);
        mOriginalWindowCallback.onContentChanged();
    }