一種無需留坑爲頁面動態添加View方案
在Activity或Fragment頁面動態添加View，有其應用場景，好比配合運營在首頁動態插入H5活動頁（以下圖手淘的雪花例示[1]）,在頁面頭部插入通知View等。本文結合ActivityLifecycleCallbacks[2]及DecorView使用，爲相似需求提供一種解決方案。
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方案概述
本文方案監聽Activity生命週期，在拿到指定Activity後，獲取PhoneWindow.mContentParent，並在mContentParent中addView。android
監聽Activity生命週期
在android API 14+ ,Application.registerActivityLifecycleCallbacks(ActivityLifecycleCallbacks callback)提供了一套回調方法，用於對Activity的生命週期事件進行集中處理。咱們可用ActivityLifecycleCallbacks玩出不少花樣，好比頁面埋點，router預處理，限制Activity實例個數，swipeback等等。在本文它keep當前activity引用。git
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獲取
Android的頁面組成[3]以下圖（注:在sdk 14+或在19+AppCompat，mContentParent不包含Actionbar，既標題欄[4]），咱們關心如何獲取mContentParent。github
在此簡單例出mContentParent的相關代碼app
/**
*Activity.setContentView，此處的getWindow返回PhoneWindow,在
*activity.attach方法中實例化
**/
public void setContentView(@LayoutRes int layoutResID) {
getWindow().setContentView(layoutResID);
initWindowDecorActionBar();
}
/**
*PhoneWindow.setContentView
**/
public void setContentView(int layoutResID) {
...
if (mContentParent == null) {
mContentParent = generateLayout(mDecor);
}
...
}
/**
* mContentParent 從DecorView中ID爲ID_ANDROID_CONTENT中賦值；ID_ANDROID_CONTENT在PhoneWindow中是一個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);
}
從上述代碼咱們能夠發現，mContentParent能夠經過activity.findViewById(android.R.id.content)獲取。ide
方案實現
此方案兩個關鍵：keep Activity實例和獲取id爲android.R.id.content的View。下面列出核心代碼。post
public class Background implements Application.ActivityLifecycleCallbacks {
/**
* 用於檢測當前APP是否運行於前臺
*/
private int appCount = 0;
private WeakReference<Activity> mActivity;
@Override
public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
}
@Override
public void onActivityStarted(Activity activity) {
appCount++;
}
@Override
public void onActivityResumed(Activity activity) {
mActivity = new WeakReference<>(activity);
}
@Override
public void onActivityPaused(Activity activity) {
}
@Override
public void onActivityStopped(Activity activity) {
appCount--;
}
@Override
public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
}
@Override
public void onActivityDestroyed(Activity activity) {
}
/**
* 判斷當前APP是否在後臺
*
* @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;
}
/**
* 獲取當前頁面的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;
}
/**
* 獲取當前運行的Activity
*
* @return
*/
public Activity getCurActivity() {
return mActivity.get();
}
}
/**
* 頁面頂部顯示通知View實例 `[5]`
**/
public class MessageBar extends FrameLayout {
private Runnable mDismissRunnable = new Runnable() {
@Override
public 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 them
if (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.
}
}
}
參考
[1] 利用動態加載實現手機淘寶的節日特效：http://www.jianshu.com/p/195e...
[2] ActivityLifecycleCallbacks： https://developer.android.com...
[3] setContentView 背後那些事兒：http://www.jianshu.com/p/0219...
[4] android.R.id.content指什麼以及一個實例：http://lingnanlu.github.io/20...
[5] snackbar：https://github.com/nispok/sna...ui
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