- 应用中响应
android.intent.action.MAIN和android.intent.category.LAUNCHER在本文中称为主界面。- 本文基于 Android O
问题现象
用PackageInstaller安装应用，在安装完成界面里点击打开，应用闪屏页打开后，按Home键回到桌面，点击桌面里的应用图标。
问题点：再打开一个闪屏页。
问题原因
应用中启动别的应用，以上问题场景使用的是 PackageManager#getLaunchIntentForPackage() 这个API，它的实现是：
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// frameworks\base\core\java\android\app\ApplicationPackageManager.java
@Override
public Intent getLaunchIntentForPackage(String packageName) {
// First see if the package has an INFO activity; the existence of
// such an activity is implied to be the desired front-door for the
// overall package (such as if it has multiple launcher entries).
Intent intentToResolve = new Intent(Intent.ACTION_MAIN);
intentToResolve.addCategory(Intent.CATEGORY_INFO);
intentToResolve.setPackage(packageName);
List<ResolveInfo> ris = queryIntentActivities(intentToResolve, 0);
// Otherwise, try to find a main launcher activity.
if (ris == null || ris.size() <= 0) {
// reuse the intent instance
intentToResolve.removeCategory(Intent.CATEGORY_INFO);
intentToResolve.addCategory(Intent.CATEGORY_LAUNCHER);
intentToResolve.setPackage(packageName); // <- 这里
ris = queryIntentActivities(intentToResolve, 0);
}
if (ris == null || ris.size() <= 0) {
return null;
}
Intent intent = new Intent(intentToResolve);
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
intent.setClassName(ris.get(0).activityInfo.packageName,
ris.get(0).activityInfo.name);
return intent;
}
正常桌面启动某个应用的实现如下：
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// Launcher3\src\com\android\launcher3\AppInfo.java
public static Intent makeLaunchIntent(Context context, LauncherActivityInfoCompat info,
UserHandleCompat user) {
long serialNumber = UserManagerCompat.getInstance(context).getSerialNumberForUser(user);
return new Intent(Intent.ACTION_MAIN)
.addCategory(Intent.CATEGORY_LAUNCHER)
.setComponent(info.getComponentName())
.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_RESET_TASK_IF_NEEDED)
.putExtra(EXTRA_PROFILE, serialNumber);
}
对比以上两种启动另一个应用的代码实现，可以发现： PackageManager#getLaunchIntentForPackage() 这个API 多了 intentToResolve.setPackage(packageName); 。
起始应用A直接使用该方法返回的 Intent 对象去启动目标应用B，该intent会被AMS增加一个flag：FLAG_ACTIVITY_BROUGHT_TO_FRONT，代码如下：
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// frameworks\base\services\core\java\com\android\server\am\ActivityStarter.java
/**
* Figure out which task and activity to bring to front when we have found an existing matching
* activity record in history. May also clear the task if needed.
* @param intentActivity Existing matching activity.
* @return {@link ActivityRecord} brought to front.
*/
private ActivityRecord setTargetStackAndMoveToFrontIfNeeded(ActivityRecord intentActivity) {
mTargetStack = intentActivity.getStack();
mTargetStack.mLastPausedActivity = null;
// If the target task is not in the front, then we need to bring it to the front...
// except... well, with SINGLE_TASK_LAUNCH it's not entirely clear. We'd like to have
// the same behavior as if a new instance was being started, which means not bringing it
// to the front if the caller is not itself in the front.
final ActivityStack focusStack = mSupervisor.getFocusedStack();
ActivityRecord curTop = (focusStack == null)
? null : focusStack.topRunningNonDelayedActivityLocked(mNotTop);
final TaskRecord topTask = curTop != null ? curTop.getTask() : null;
if (topTask != null
&& (topTask != intentActivity.getTask() || topTask != focusStack.topTask())
&& !mAvoidMoveToFront) {
mStartActivity.intent.addFlags(Intent.FLAG_ACTIVITY_BROUGHT_TO_FRONT); // <- 这里
if (mSourceRecord == null || (mSourceStack.topActivity() != null &&
mSourceStack.topActivity().getTask() == mSourceRecord.getTask())) {
// We really do want to push this one into the user's face, right now.
if (mLaunchTaskBehind && mSourceRecord != null) {
intentActivity.setTaskToAffiliateWith(mSourceRecord.getTask());
}
mMovedOtherTask = true;
// ...
}
如果该B应用启动后置后台，那么会根据B应用的主界面的lauchMode创建或复用任务栈里的对象，会有意想不到的结果。比如：如果B应用的主界面launchMode是standard，那么会有第二个主界面被创建在任务栈里。
更详细原因分析请参考文章：关于Android应用回到桌面会重复打开闪屏页
解决方案
第一种
在起始应用A里发起跳转时：
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Intent intent = context.getPackageManager().getLaunchIntentForPackage(packageName);
intent.setPackage(null); // 加上这句代码
context.startActivity(intent);
第二种
在目标应用B的主界面onCreate里，添加：
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super.onCreate(savedInstanceState);
if ((getIntent().getFlags() & Intent.FLAG_ACTIVITY_BROUGHT_TO_FRONT)> 0) {
/**为了防止重复启动多个闪屏页面**/
finish();
return;
}