Android(安卓)4.0 Launcher2源码分析——Workspace切换AllApps流程

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文中如有纰漏之处，望不吝指教~~~欢迎讨论，共同学习~~~

进入AllApps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:

[java] view plain copy

privatevoidsetupViews(){
......
//Gettheallappsbutton
mAllAppsButton=findViewById(R.id.all_apps_button);
if(mAllAppsButton!=null){
mAllAppsButton.setOnTouchListener(newView.OnTouchListener(){
@Override
publicbooleanonTouch(Viewv,MotionEventevent){
//(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);
}
returnfalse;
}
});
}
......
}

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。

[java] view plain copy

publicvoidonTouchDownAllAppsButton(Viewv){
//Providethesamehapticfeedbackthatthesystemoffersforvirtualkeys.
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

[java] view plain copy

voidresetLayout(){
......
allAppsButton.setOnClickListener(newView.OnClickListener(){
@Override
publicvoidonClick(android.view.Viewv){
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。 [java] view plain copy

/**
*Eventhandlerforthe"grid"buttonthatappearsonthehomescreen,which
*entersallappsmode.
*
*@paramvTheviewthatwasclicked.
*/
publicvoidonClickAllAppsButton(Viewv){
showAllApps(true);
}

接着进入showAllApps()方法。 [java] view plain copy

voidshowAllApps(booleananimated){
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();
//Hidethesearchbarandhotseat
//将searchBar隐藏起来
mSearchDropTargetBar.hideSearchBar(animated);
//Changethestate*after*we'vecalledallthetransitioncode
//将状态mState从WORKSPACE切换到APPS_CUSTOMIZE
mState=State.APPS_CUSTOMIZE;
//Pausetheauto-advanceofwidgetsuntilweareoutofAllApps
//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();
//Sendanaccessibilityeventtoannouncethecontextchange
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()：

[java] view plain copy

/**
*Zoomthecameraoutfromtheworkspacetoreveal'toView'.
*Assumesthattheviewtoshowisanchoredateithertheverytoporverybottom
*ofthescreen.
*@paramtoStateThestatetozoomoutto.MustbeAPPS_CUSTOMIZE.
*/
privatevoidcameraZoomOut(StatetoState,booleananimated,finalbooleanspringLoaded){
......
//设置缩放时的轴心
setPivotsForZoom(toView,toState,scale);
//ShrinkworkspacesawayifgoingtoAppsCustomizefromworkspace
//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
finalValueAnimatorscaleAnim=ValueAnimator.ofFloat(0f,1f).setDuration(duration);
scaleAnim.setInterpolator(newWorkspace.ZoomOutInterpolator());
scaleAnim.addUpdateListener(newLauncherAnimatorUpdateListener(){
publicvoidonAnimationUpdate(floata,floatb){
((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
ValueAnimatoralphaAnim=ValueAnimator.ofFloat(0f,1f).setDuration(fadeDuration);
alphaAnim.setInterpolator(newDecelerateInterpolator(1.5f));
alphaAnim.addUpdateListener(newLauncherAnimatorUpdateListener(){
publicvoidonAnimationUpdate(floata,floatb){
//don'tneedtoinvalidatebecausewedosoabove
toView.setFastAlpha(a*0f+b*1f);
}
});
alphaAnim.setStartDelay(startDelay);
alphaAnim.start();
if(toViewinstanceofLauncherTransitionable){
//切换开始时，调用AppsCustomizeTabHost.onLauncherTransitionStart()方法
((LauncherTransitionable)toView).onLauncherTransitionStart(instance,scaleAnim,
false);
}
scaleAnim.addListener(newAnimatorListenerAdapter(){
booleananimationCancelled=false;
@Override
publicvoidonAnimationStart(Animatoranimation){
updateWallpaperVisibility(true);
//Preparetheposition
toView.setTranslationX(0.0f);
toView.setTranslationY(0.0f);
toView.setVisibility(View.VISIBLE);
toView.bringToFront();
}
@Override
publicvoidonAnimationEnd(Animatoranimation){
//Ifwedon'tsetthefinalscalevalueshere,ifthisanimationiscancelled
//itwillhavethewrongscalevalueandsubsequentcameraPananimationswill
//notfixthat
toView.setScaleX(1.0f);
toView.setScaleY(1.0f);
if(toViewinstanceofLauncherTransitionable){
//当切换过程完成时，调用AppsCustomizeTabHost.onLauncherTransitionEnd()方法
((LauncherTransitionable)toView).onLauncherTransitionEnd(instance,
scaleAnim,false);
}
......
}
@Override
publicvoidonAnimationCancel(Animatoranimation){
animationCancelled=true;
}
});
//toViewshouldappearrightattheendoftheworkspaceshrinkanimation
if(mStateAnimation!=null)mStateAnimation.cancel();
mStateAnimation=newAnimatorSet();
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。

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