Android 4.0 Launcher2源码分析——Workspace切换AllApps流程

本文来自http://blog.csdn.net/chenshaoyang0011 转载请申明文章出处！

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进入All Apps界面是通过点击Hotseat中的allAppsButton触发事件，通过前面的分析，已经知道在setupViews()方法中，就为button设置好了onTouchListener:

private void setupViews() {
......
// Get the all apps button
mAllAppsButton = findViewById(R.id.all_apps_button);
if (mAllAppsButton != null) {
mAllAppsButton.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
//(MotionEvent.ACTION_POINTER_1_DOWN & MotionEvent.ACTION_MASK)
//(MotionEvent.ACTION_POINTER_2_DOWN & MotionEvent.ACTION_MASK)
//(MotionEvent.ACTION_POINTER_3_DOWN & MotionEvent.ACTION_MASK)
// == MotionEvent.ACTION_DOWN
if ((event.getAction() & MotionEvent.ACTION_MASK) == MotionEvent.ACTION_DOWN) {
onTouchDownAllAppsButton(v);
}
return false;
}
});
}
......
}

这里简单说明下，为什么在判断事件的时候不直接使用event.getAction() == MotionEvent.ACTION_DOWN，而是采用(event.getAction() & MotionEvent.ACTION_MASK) ==MotionEvent.ACTION_DOWN呢？查看文档，我们可以发现ACTION_MASK的值为0x000000ff，二进制的值为11111111。ACTION_DOWN的值为0x00000000，二进制为00000000。在真实的设备中通常支持多点触控，但根据直观的判断，多指“按下”和单指“按下”都属于“按下”。Android中ACTION_MASK恰恰是为了解决这个问题而存在的因为(MotionEvent.ACTION_POINTER_1_DOWN & MotionEvent.ACTION_MASK) == MotionEvent.ACTION_DOWN, (MotionEvent.ACTION_POINTER_2_DOWN  &  MotionEvent.ACTION_MASK) == MotionEvent.ACTION_DOWN,(MotionEvent.ACTION_POINTER_3_DOWN & MotionEvent.ACTION_MASK) == MotionEvent.ACTION_DOWN。这就是为什么要先“与”再判断的原因了。ACTION_DOWN被触发后，onTouchDownAllAppsButton()被调用。

public void onTouchDownAllAppsButton(View v) {
// Provide the same haptic feedback that the system offers for virtual keys.
v.performHapticFeedback(HapticFeedbackConstants.VIRTUAL_KEY);
}

在onTouchDownAllAppsButton()中为ACTION_DOWN事件提供了触感反馈（振动反馈）。

接着，顺着启动的过程，进入到了Hotseat.resetLayout()方法中

void resetLayout() {
......
allAppsButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(android.view.View v) {
if (mLauncher != null) {
mLauncher.onClickAllAppsButton(v);
}
}
});
......
}

这里为allAppsButton设置了OnClickListener，当allAppsButton被点击后，会调用Launcher.onClickAllAppsButton()方法。

/**
* Event handler for the "grid" button that appears on the home screen, which
* enters all apps mode.
*
* @param v The view that was clicked.
*/
public void onClickAllAppsButton(View v) {
showAllApps(true);
}

接着进入showAllApps()方法。

void showAllApps(boolean animated) {
if (mState != State.WORKSPACE) return;

//显示apps_customize也就是AllApps页面，切换时有缩放和渐显的动画
cameraZoomOut(State.APPS_CUSTOMIZE, animated, false);
mAppsCustomizeTabHost.requestFocus();

// Hide the search bar and hotseat
//将searchBar隐藏起来
mSearchDropTargetBar.hideSearchBar(animated);

// Change the state *after* we've called all the transition code
//将状态mState从WORKSPACE切换到APPS_CUSTOMIZE
mState = State.APPS_CUSTOMIZE;

// Pause the auto-advance of widgets until we are out of AllApps
//停止对AppWidget的自动更新
mUserPresent = false;
updateRunning();
//将桌面上打开的文件夹关闭
closeFolder();

// Send an accessibility event to announce the context change
getWindow().getDecorView().sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_SELECTED);
}

进入方法后可以看到，最主要的功能是在cameraZoomOut()方法中，以动画的方式来显示AllApps页。接着隐藏了SearchDropTargetBar和Hotseat。为了节省资源，关闭了AppWidget的自动更新。下面进入cameraZoomOut()：

/**
* Zoom the camera out from the workspace to reveal 'toView'.
* Assumes that the view to show is anchored at either the very top or very bottom
* of the screen.
* @param toState The state to zoom out to. Must be APPS_CUSTOMIZE.
*/
private void cameraZoomOut(State toState, boolean animated, final boolean springLoaded) {
......

//设置缩放时的轴心
setPivotsForZoom(toView, toState, scale);

// Shrink workspaces away if going to AppsCustomize from workspace
//缩小workspaces然后让它消失。
mWorkspace.changeState(Workspace.State.SMALL, animated);

if (animated) {
//如果需要动画，就是用scaleAnim来实现缩放的动画效果
final ValueAnimator scaleAnim = ValueAnimator.ofFloat(0f, 1f).setDuration(duration);
scaleAnim.setInterpolator(new Workspace.ZoomOutInterpolator());
scaleAnim.addUpdateListener(new LauncherAnimatorUpdateListener() {
public void onAnimationUpdate(float a, float b) {
((View) toView.getParent()).invalidate();
toView.fastInvalidate();
toView.setFastScaleX(a * scale + b * 1f);
toView.setFastScaleY(a * scale + b * 1f);
}
});

toView.setVisibility(View.VISIBLE);
toView.setFastAlpha(0f);
//使用alphaAnim来实现渐显的动画效果
ValueAnimator alphaAnim = ValueAnimator.ofFloat(0f, 1f).setDuration(fadeDuration);
alphaAnim.setInterpolator(new DecelerateInterpolator(1.5f));
alphaAnim.addUpdateListener(new LauncherAnimatorUpdateListener() {
public void onAnimationUpdate(float a, float b) {
// don't need to invalidate because we do so above
toView.setFastAlpha(a * 0f + b * 1f);
}
});
alphaAnim.setStartDelay(startDelay);
alphaAnim.start();

if (toView instanceof LauncherTransitionable) {
//切换开始时，调用AppsCustomizeTabHost.onLauncherTransitionStart()方法
((LauncherTransitionable) toView).onLauncherTransitionStart(instance, scaleAnim,
false);
}
scaleAnim.addListener(new AnimatorListenerAdapter() {
boolean animationCancelled = false;

@Override
public void onAnimationStart(Animator animation) {
updateWallpaperVisibility(true);
// Prepare the position
toView.setTranslationX(0.0f);
toView.setTranslationY(0.0f);
toView.setVisibility(View.VISIBLE);
toView.bringToFront();
}
@Override
public void onAnimationEnd(Animator animation) {
// If we don't set the final scale values here, if this animation is cancelled
// it will have the wrong scale value and subsequent cameraPan animations will
// not fix that
toView.setScaleX(1.0f);
toView.setScaleY(1.0f);
if (toView instanceof LauncherTransitionable) {
//当切换过程完成时，调用AppsCustomizeTabHost.onLauncherTransitionEnd()方法
((LauncherTransitionable) toView).onLauncherTransitionEnd(instance,
scaleAnim, false);
}

......
}

@Override
public void onAnimationCancel(Animator animation) {
animationCancelled = true;
}
});

// toView should appear right at the end of the workspace shrink animation

if (mStateAnimation != null) mStateAnimation.cancel();
mStateAnimation = new AnimatorSet();
mStateAnimation.play(scaleAnim).after(startDelay);
mStateAnimation.start();
} else {
//不需要动画效果
......
}

这里演示了使用ValueAnimator来实现动画效果的方式。动画结束之后，页面的切换就完成了。