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。