在Activity或Fragment页面动态添加View，有其应用场景，比如配合运营在首页动态插入H5活动页（如下图手淘的雪花例示[1]）,在页面头部插入通知View等。本文结合ActivityLifecycleCallbacks[2]及DecorView使用，为类似需求提供一种解决方案。
方案概述
本文方案监听Activity生命周期，在拿到指定Activity后，获取PhoneWindow.mContentParent，并在mContentParent中addView。
监听Activity生命周期
在android API 14+ ,Application.registerActivityLifecycleCallbacks(ActivityLifecycleCallbacks callback)提供了一套回调方法，用于对Activity的生命周期事件进行集中处理。我们可用ActivityLifecycleCallbacks玩出很多花样，比如页面埋点，router预处理，限制Activity实例个数，swipeback等等。在本文它keep当前activity引用。
public interface ActivityLifecycleCallbacks {void onActivityCreated(Activity activity, Bundle savedInstanceState);void onActivityStarted(Activity activity);void onActivityResumed(Activity activity);void onActivityPaused(Activity activity);void onActivityStopped(Activity activity);void onActivitySaveInstanceState(Activity activity, Bundle outState);void onActivityDestroyed(Activity activity);
}
PhoneWindow.mContentParent获取
Android的页面组成[3]如下图（注:在sdk 14+或在19+AppCompat，mContentParent不包含Actionbar，既标题栏[4]），我们关心如何获取mContentParent。
在此简单例出mContentParent的相关代码
/***Activity.setContentView，此处的getWindow返回PhoneWindow,在*activity.attach方法中实例化**/public void setContentView(@LayoutRes int layoutResID) {getWindow().setContentView(layoutResID);initWindowDecorActionBar();}/***PhoneWindow.setContentView**/ public void setContentView(int layoutResID) {...if (mContentParent == null) {mContentParent = generateLayout(mDecor);}...}/*** mContentParent 从DecorView中ID为ID_ANDROID_CONTENT中赋值；ID_ANDROID_CONTENT在PhoneWindow中是一个int常量* public static final int ID_ANDROID_CONTENT = com.android.internal.R.id.content;**/ protected ViewGroup generateLayout(DecorView decor) {...ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);if (contentParent == null) {throw new RuntimeException("Window couldn't find content container view");}...return contentParent;}/***Activity.findViewById**/
public View findViewById(@IdRes int id) {return getWindow().findViewById(id);}
/***PhoneWindow.findViewById
**/
public View findViewById(@IdRes int id) {return getDecorView().findViewById(id);}
从上述代码我们可以发现，mContentParent可以通过activity.findViewById(android.R.id.content)获取。
方案实现
此方案两个关键：keep Activity实例和获取id为android.R.id.content的View。下面列出核心代码。
public class Background implements Application.ActivityLifecycleCallbacks {/*** 用于检测当前APP是否运行于前台*/private int appCount = 0;private WeakReference<Activity> mActivity;@Overridepublic void onActivityCreated(Activity activity, Bundle savedInstanceState) {}@Overridepublic void onActivityStarted(Activity activity) {appCount++;}@Overridepublic void onActivityResumed(Activity activity) {mActivity = new WeakReference<>(activity);}@Overridepublic void onActivityPaused(Activity activity) {}@Overridepublic void onActivityStopped(Activity activity) {appCount--;}@Overridepublic void onActivitySaveInstanceState(Activity activity, Bundle outState) {}@Overridepublic void onActivityDestroyed(Activity activity) {}/*** 判断当前APP是否在后台** @param context* @return*/public boolean inBackRunning(final Context context) {PowerManager pm = (PowerManager) context.getSystemService(Context.POWER_SERVICE);boolean isScreenOn = true;if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT_WATCH) {isScreenOn = pm.isInteractive();} else {isScreenOn = pm.isScreenOn();}boolean isOnForeground = appCount > 0;return !isScreenOn || !isOnForeground;}/*** 获取当前页面的Fragment** @return*/public Fragment getCurFragment() {if (mActivity == null ||mActivity.get()==null|| !(mActivity.get() instanceof FragmentActivity)) {return null;}FragmentManager fragManager = ((FragmentActivity) mActivity.get()).getSupportFragmentManager();if (fragManager.getFragments() != null) {List<Fragment> fragments = fragManager.getFragments();for (Fragment fragment : fragments) {if (fragment != null && fragment.isVisible())return fragment;}return null;}return null;}/*** 获取当前运行的Activity** @return*/public Activity getCurActivity() {return mActivity.get();}
}/*** 页面顶部显示通知View实例 `[5]`**/
public class MessageBar extends FrameLayout {private Runnable mDismissRunnable = new Runnable() {@Overridepublic void run() {dismiss();}};private AppMessage mAppMessage = new AppMessage.Builder().build();public MessageBar(Context context) {super(context);}public MessageBar(Context context, AttributeSet attrs) {super(context, attrs);}public MessageBar(Context context, AttributeSet attrs, int defStyle) {super(context, attrs, defStyle);}public static MessageBar with(Context context) {return new MessageBar(context);}public MessageBar setAppMessage(AppMessage appMessage) {if (appMessage != null) {mAppMessage = appMessage;}return this;}public void dismiss() {finish();}private void finish() {clearAnimation();ViewGroup parent = (ViewGroup) getParent();if (parent != null) {parent.removeView(this);}}/*** Displays the {@link MessageBar} at the bottom of the* {@link Activity} provided.** @param targetActivity*/public void show(Activity targetActivity) {ViewGroup root = (ViewGroup) targetActivity.findViewById(android.R.id.content);MarginLayoutParams params = init(targetActivity, root);showInternal(targetActivity, params, root);MediaUtil.getInstance(targetActivity).playSound(R.raw.im_notification, targetActivity);VibratorUtil.vibrator(targetActivity);}private MarginLayoutParams init(Activity targetActivity, ViewGroup parent) {FrameLayout layout = (FrameLayout) LayoutInflater.from(targetActivity).inflate(R.layout.mercury_template, this, true);customUI(layout);MarginLayoutParams params;params = createMarginLayoutParams(parent, LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT);return params;}private void customUI(FrameLayout layout) {//TODO init custom view }private static MarginLayoutParams createMarginLayoutParams(ViewGroup viewGroup, int width, int height) {if (viewGroup instanceof FrameLayout) {LayoutParams params = new LayoutParams(width, height);params.gravity = TOP;return params;} else if (viewGroup instanceof RelativeLayout) {RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(width, height);params.addRule(RelativeLayout.ALIGN_PARENT_TOP, RelativeLayout.TRUE);return params;} else if (viewGroup instanceof LinearLayout) {LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(width, height);params.gravity = TOP;return params;} else {throw new IllegalStateException("Requires FrameLayout or RelativeLayout for the parent of Snackbar");}}private void showInternal(Activity targetActivity, MarginLayoutParams params, ViewGroup parent) {parent.removeView(this);// We need to make sure the MessageBar elevation is at least as high as// any other child views, or it will be displayed underneath themif (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {for (int i = 0; i < parent.getChildCount(); i++) {View otherChild = parent.getChildAt(i);float elvation = otherChild.getElevation();if (elvation > getElevation()) {setElevation(elvation);}}}parent.addView(this, params);bringToFront();// As requested in the documentation for bringToFront()if (Build.VERSION.SDK_INT < Build.VERSION_CODES.KITKAT) {parent.requestLayout();parent.invalidate();}focusForAccessibility(this);startTimer();}private void startTimer() {postDelayed(mDismissRunnable, 3000);}private void focusForAccessibility(View view) {final AccessibilityEvent event = AccessibilityEvent.obtain(AccessibilityEvent.TYPE_VIEW_FOCUSED);AccessibilityEventCompat.asRecord(event).setSource(view);try {view.sendAccessibilityEventUnchecked(event);} catch (IllegalStateException e) {// accessibility is off.}}}
参考
[1] 利用动态加载实现手机淘宝的节日特效：http://www.jianshu.com/p/195e...
[2] ActivityLifecycleCallbacks： https://developer.android.com...
[3] setContentView 背后那些事儿：http://www.jianshu.com/p/0219...
[4] android.R.id.content指什么以及一个实例：http://lingnanlu.github.io/20...
[5] snackbar：https://github.com/nispok/sna...
