Android 从源码分析View层次之ActionMode

转载请注明出处：（http://blog.csdn.net/qq_35071078/article/details/72859905）

我们都知道，android最上层的view是一个DecorView，它下面又会有多种不同的ViewGroup（具体是一个什么样子的View，那是activity根据我们定义的属性来自动加载布局的），而我们写的布局就会加载到DecorView的某个子View下。刚好最近闲着，准备自己看一看android的view层次，于是乎，我用递归打印出了一个activity中的View层次。发现DecorView下总是会有一个ViewStub，

第一反应这个ViewStub应该是加载ActionBar的，但是发现ActionBar有它自己的布局，那么这个ViewStub到底是干嘛的？在翻阅各大论坛和博客以及stackoverflow之后，终于知道这里的ViewStub是干啥的了，所以写一篇博客总结一下。
大家如果想了解view是怎么加载出来的可以看看泓洋大神的 Android 源码解析 之 setContentView写的很清晰的

ActionMode 是什么？

官方的解释是：表示用户界面的上下文模式。动作模式可用于提供替代交互模式和取代正常的UI部件直到完成。良好的动作模式的实例包括文本选择和上下文动作。
通俗点讲，它就是android里一种menu的方式，方式有很多，其他的我就不说了，我只说ActionMode，ActionMode是临时占据了ActionBar的位置的一个menu。这样就知道这个ViewStub是干啥的了，就是用来加载我们的菜单的。

ActionMode 怎么用？

只需要在activity里调用 startActionMode(Callback callback)这个方法就可以了。
例如我这里实例化了一个Callback：

private ActionMode.Callback mCallback = new ActionMode.Callback() {        @Override        public boolean onPrepareActionMode(ActionMode mode, Menu menu) {            return false;        }        @Override        public void onDestroyActionMode(ActionMode mode) {            // TODO Auto-generated method stub        }        @Override        public boolean onCreateActionMode(ActionMode mode, Menu menu) {            MenuInflater inflater = mode.getMenuInflater();            inflater.inflate(R.menu.actionmode, menu);            return true;        }        @Override        public boolean onActionItemClicked(ActionMode mode, MenuItem item) {            boolean ret = false;            if (item.getItemId() == R.id.actionmode_cancel) {                mode.finish();                ret = true;            }            return ret;        }    };

然后在需要的地方调用：

startActionMode(mCallback)

就ok了，activity会在适当的时候回调一个方法：

    @Nullable    @Override    public ActionMode onWindowStartingActionMode(ActionMode.Callback callback) {        return super.onWindowStartingActionMode(callback);    }

类似这样：

startActionMode的实现过程

首先,我是在API 23上进行分析的，而且我查看的源码不是supportv7下的源码。就是普通的activity。关于如何查看源码，大家可以查看这篇博客源码查看方法
我们进入到activity中的startActionMode这个方法：

    @Nullable    public ActionMode startActionMode(ActionMode.Callback callback) {        return mWindow.getDecorView().startActionMode(callback);    }

发现它是调用了DecorView的startActionMode，我们进入到这个方法：

@Override    public ActionMode startActionModeForChild(View originalView,            ActionMode.Callback callback) {        return startActionModeForChild(originalView, callback, ActionMode.TYPE_PRIMARY);    }    @Override    public ActionMode startActionModeForChild(            View child, ActionMode.Callback callback, int type) {        return startActionMode(child, callback, type);    }    @Override    public ActionMode startActionMode(ActionMode.Callback callback) {        return startActionMode(callback, ActionMode.TYPE_PRIMARY);    }    @Override    public ActionMode startActionMode(ActionMode.Callback callback, int type) {        return startActionMode(this, callback, type);    }    private ActionMode startActionMode(            View originatingView, ActionMode.Callback callback, int type) {            //最终会调用这个方法        ActionMode.Callback2 wrappedCallback = new ActionModeCallback2Wrapper(callback);        ActionMode mode = null;        if (mWindow.getCallback() != null && !mWindow.isDestroyed()) {            try {                mode = mWindow.getCallback().onWindowStartingActionMode(wrappedCallback, type);            } catch (AbstractMethodError ame) {                // Older apps might not implement the typed version of this method.                if (type == ActionMode.TYPE_PRIMARY) {                    try {                        mode = mWindow.getCallback().onWindowStartingActionMode(                                wrappedCallback);                    } catch (AbstractMethodError ame2) {                        // Older apps might not implement this callback method at all.                    }                }            }        }        if (mode != null) {            if (mode.getType() == ActionMode.TYPE_PRIMARY) {                cleanupPrimaryActionMode();                mPrimaryActionMode = mode;            } else if (mode.getType() == ActionMode.TYPE_FLOATING) {                if (mFloatingActionMode != null) {                    mFloatingActionMode.finish();                }                mFloatingActionMode = mode;            }        } else {            mode = createActionMode(type, wrappedCallback, originatingView);            if (mode != null && wrappedCallback.onCreateActionMode(mode, mode.getMenu())) {                setHandledActionMode(mode);            } else {                mode = null;            }        }        if (mode != null && mWindow.getCallback() != null && !mWindow.isDestroyed()) {            try {                mWindow.getCallback().onActionModeStarted(mode);            } catch (AbstractMethodError ame) {                // Older apps might not implement this callback method.            }        }        return mode;    }

其他的不用管，看这一句：

mode = mWindow.getCallback().onWindowStartingActionMode(wrappedCallback, type);

这里的mWindow.getCallback()实际上就是activity，因为activity实现了这个接口，所以这个地方就会执行到了前面说的activity里面的onWindowStartingActionMode(wrappedCallback, type)。那么再在activity中来查看这个方法：

    @Nullable    @Override    public ActionMode onWindowStartingActionMode(ActionMode.Callback callback) {        // Only Primary ActionModes are represented in the ActionBar.        if (mActionModeTypeStarting == ActionMode.TYPE_PRIMARY) {            initWindowDecorActionBar();            if (mActionBar != null) {                return mActionBar.startActionMode(callback);            }        }        return null;    }

这里有 initWindowDecorActionBar()，看名字就知道大致的意思了，是用来初始化DecorActionBar的。

    private void initWindowDecorActionBar() {        Window window = getWindow();        // Initializing the window decor can change window feature flags.        // Make sure that we have the correct set before performing the test below.        window.getDecorView();        if (isChild() || !window.hasFeature(Window.FEATURE_ACTION_BAR) || mActionBar != null) {            return;        }        mActionBar = new WindowDecorActionBar(this);        mActionBar.setDefaultDisplayHomeAsUpEnabled(mEnableDefaultActionBarUp);        mWindow.setDefaultIcon(mActivityInfo.getIconResource());        mWindow.setDefaultLogo(mActivityInfo.getLogoResource());    }

在initWindowDecorActionBar()方法之后，activity会调用mActionBar.startActionMode(callback)，那么刚好这里有实例化了mActionBar.

mActionBar = new WindowDecorActionBar(this);

所以说最终就是通过WindowDecorActionBar来完成相应的操作了。那么在去看看这个类里的方法：

    public ActionMode startActionMode(ActionMode.Callback callback) {        if (mActionMode != null) {            mActionMode.finish();        }        mOverlayLayout.setHideOnContentScrollEnabled(false);        mContextView.killMode();        ActionModeImpl mode = new ActionModeImpl(mContextView.getContext(), callback);        if (mode.dispatchOnCreate()) {            // This needs to be set before invalidate() so that it calls            // onPrepareActionMode()            mActionMode = mode;            mode.invalidate();            mContextView.initForMode(mode);            animateToMode(true);            if (mSplitView != null && mContextDisplayMode == CONTEXT_DISPLAY_SPLIT) {                // TODO animate this                if (mSplitView.getVisibility() != View.VISIBLE) {                    mSplitView.setVisibility(View.VISIBLE);                    if (mOverlayLayout != null) {                        mOverlayLayout.requestApplyInsets();                    }                }            }            mContextView.sendAccessibilityEvent(AccessibilityEvent.TYPE_WINDOW_STATE_CHANGED);            return mode;        }        return null;    }

这里有个方法 animateToMode(true);肯定是对布局进行一些操作，进去看看：

    void animateToMode(boolean toActionMode) {        if (toActionMode) {            showForActionMode();        } else {            hideForActionMode();        }        if (shouldAnimateContextView()) {            Animator fadeIn, fadeOut;            if (toActionMode) {                fadeOut = mDecorToolbar.setupAnimatorToVisibility(View.GONE,                        FADE_OUT_DURATION_MS);                fadeIn = mContextView.setupAnimatorToVisibility(View.VISIBLE,                        FADE_IN_DURATION_MS);            } else {                fadeIn = mDecorToolbar.setupAnimatorToVisibility(View.VISIBLE,                        FADE_IN_DURATION_MS);                fadeOut = mContextView.setupAnimatorToVisibility(View.GONE,                        FADE_OUT_DURATION_MS);            }            AnimatorSet set = new AnimatorSet();            set.playSequentially(fadeOut, fadeIn);            set.start();        } else {            if (toActionMode) {                mDecorToolbar.setVisibility(View.GONE);                mContextView.setVisibility(View.VISIBLE);            } else {                mDecorToolbar.setVisibility(View.VISIBLE);                mContextView.setVisibility(View.GONE);            }        }        // mTabScrollView's visibility is not affected by action mode.    }

这里有两个方法：showForActionMode(); hideForActionMode();一看就是用来隐藏或者显示布局的

    private void showForActionMode() {        if (!mShowingForMode) {            mShowingForMode = true;            if (mOverlayLayout != null) {                mOverlayLayout.setShowingForActionMode(true);            }            updateVisibility(false);        }    }    private void hideForActionMode() {        if (mShowingForMode) {            mShowingForMode = false;            if (mOverlayLayout != null) {                mOverlayLayout.setShowingForActionMode(false);            }            updateVisibility(false);        }    }

他们最终会调用updateVisibility()这个方法：

    private void updateVisibility(boolean fromSystem) {        // Based on the current state, should we be hidden or shown?        final boolean shown = checkShowingFlags(mHiddenByApp, mHiddenBySystem,                mShowingForMode);        if (shown) {            if (!mNowShowing) {                mNowShowing = true;                doShow(fromSystem);            }        } else {            if (mNowShowing) {                mNowShowing = false;                doHide(fromSystem);            }        }    }

updateVisibility()紧接着会调用doShow(fromSystem);doHide(fromSystem);

public void doShow(boolean fromSystem) {        if (mCurrentShowAnim != null) {            mCurrentShowAnim.end();        }        mContainerView.setVisibility(View.VISIBLE);        if (mCurWindowVisibility == View.VISIBLE && (mShowHideAnimationEnabled                || fromSystem)) {            mContainerView.setTranslationY(0); // because we're about to ask its window loc            float startingY = -mContainerView.getHeight();            if (fromSystem) {                int topLeft[] = {0, 0};                mContainerView.getLocationInWindow(topLeft);                startingY -= topLeft[1];            }            mContainerView.setTranslationY(startingY);            AnimatorSet anim = new AnimatorSet();            ObjectAnimator a = ObjectAnimator.ofFloat(mContainerView, View.TRANSLATION_Y, 0);            a.addUpdateListener(mUpdateListener);            AnimatorSet.Builder b = anim.play(a);            if (mContentAnimations && mContentView != null) {                b.with(ObjectAnimator.ofFloat(mContentView, View.TRANSLATION_Y,                        startingY, 0));            }            if (mSplitView != null && mContextDisplayMode == CONTEXT_DISPLAY_SPLIT) {                mSplitView.setTranslationY(mSplitView.getHeight());                mSplitView.setVisibility(View.VISIBLE);                b.with(ObjectAnimator.ofFloat(mSplitView, View.TRANSLATION_Y, 0));            }            anim.setInterpolator(AnimationUtils.loadInterpolator(mContext,                    com.android.internal.R.interpolator.decelerate_cubic));            anim.setDuration(250);            // If this is being shown from the system, add a small delay.            // This is because we will also be animating in the status bar,            // and these two elements can't be done in lock-step.  So we give            // a little time for the status bar to start its animation before            // the action bar animates.  (This corresponds to the corresponding            // case when hiding, where the status bar has a small delay before            // starting.)            anim.addListener(mShowListener);            mCurrentShowAnim = anim;            anim.start();        } else {            mContainerView.setAlpha(1);            mContainerView.setTranslationY(0);            if (mContentAnimations && mContentView != null) {                mContentView.setTranslationY(0);            }            if (mSplitView != null && mContextDisplayMode == CONTEXT_DISPLAY_SPLIT) {                mSplitView.setAlpha(1);                mSplitView.setTranslationY(0);                mSplitView.setVisibility(View.VISIBLE);            }            mShowListener.onAnimationEnd(null);        }        if (mOverlayLayout != null) {            mOverlayLayout.requestApplyInsets();        }    }    public void doHide(boolean fromSystem) {        if (mCurrentShowAnim != null) {            mCurrentShowAnim.end();        }        if (mCurWindowVisibility == View.VISIBLE && (mShowHideAnimationEnabled                || fromSystem)) {            mContainerView.setAlpha(1);            mContainerView.setTransitioning(true);            AnimatorSet anim = new AnimatorSet();            float endingY = -mContainerView.getHeight();            if (fromSystem) {                int topLeft[] = {0, 0};                mContainerView.getLocationInWindow(topLeft);                endingY -= topLeft[1];            }            ObjectAnimator a = ObjectAnimator.ofFloat(mContainerView, View.TRANSLATION_Y, endingY);            a.addUpdateListener(mUpdateListener);            AnimatorSet.Builder b = anim.play(a);            if (mContentAnimations && mContentView != null) {                b.with(ObjectAnimator.ofFloat(mContentView, View.TRANSLATION_Y,                        0, endingY));            }            if (mSplitView != null && mSplitView.getVisibility() == View.VISIBLE) {                mSplitView.setAlpha(1);                b.with(ObjectAnimator.ofFloat(mSplitView, View.TRANSLATION_Y,                        mSplitView.getHeight()));            }            anim.setInterpolator(AnimationUtils.loadInterpolator(mContext,                    com.android.internal.R.interpolator.accelerate_cubic));            anim.setDuration(250);            anim.addListener(mHideListener);            mCurrentShowAnim = anim;            anim.start();        } else {            mHideListener.onAnimationEnd(null);        }    }

这里面就是各种动画了。

另外总结一下

这是我画的一个view层次图，左边的是普通的Activity的，右边的是supportv7下的Activity也就是AppCompatActivity的。但是会发现，在Appcompatctivity中使用startActionMode，并不会将布局加载到ViewStub中去，而是会在ActionBarLayout下创建一个布局。
这个图的层次也不是绝对的，到底是什么样的根布局，都是由于activity根据我们自己设定的某些属性或者参数来决定的。比如说style里面的很多属性，我随便列举几个：

<item name="windowNoTitle">false</item>//这个是针对activity的<item name="android:windowNoTitle">false</item>//这个是针对AppCompatActivity的

到底加载什么布局大家可以去网上搜搜android布局到底是如何加载出来的，或者是搜索setContentView到底干了啥。