onActivityResult 与 launchMode="singleTask"？

Posted 2023-04-14

【中文标题】onActivityResult 与 launchMode="singleTask"？

【英文标题】：onActivityResult With launchMode="singleTask"?

【发布时间】：2012-02-16 02:52:55

【问题描述】：

当您尝试使用startActivityForResult 获取具有launchMode="singleTask" 的Activity 时；它不会返回任何带有onActivityResult 的值，并且当您设置launchMode="standard" 时；一切正常，但系统要求说这个Activity 必须是singleTask，有没有办法解决这个问题？

【参考方案1】：

startActivityForResult 的文档说：

For example, if the activity you are launching uses the singleTask launch mode,
it will not run in your task and thus you will immediately receive a cancel result.

似乎没有办法解决这个问题。

如果您是被调用 Activity 的开发者，那么您可以让它在某些结果可用时发送广播。然后调用的 Activity 可以列出这个广播。

【讨论】：

那么如何防止在 onClick 中创建多个实例（例如列表视图）？

【参考方案2】：

答案显示在 ActivityStackSupervisor 类的函数 startActivityUncheckedLocked 中。 在android 5.x之前，启动一个activity时，会先检查launchMode，如果launchMode是singleTask或者singleInstance，会在launchFlags中加上FLAG_ACTIVITY_NEW_TASK。如果活动的launchFlags 包含FLAG_ACTIVITY_NEW_TASK，它会立即发回一个取消，让新任务继续正常启动，而不依赖于它的发起者。

if (sourceRecord == null) 
    // This activity is not being started from another...  in this
    // case we -always- start a new task.
    if ((launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK) == 0) 
        Slog.w(TAG, "startActivity called from non-Activity context; forcing " +
                "Intent.FLAG_ACTIVITY_NEW_TASK for: " + intent);
        launchFlags |= Intent.FLAG_ACTIVITY_NEW_TASK;
    
 else if (sourceRecord.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE) 
    // The original activity who is starting us is running as a single
    // instance...  this new activity it is starting must go on its
    // own task.
    launchFlags |= Intent.FLAG_ACTIVITY_NEW_TASK;
 else if (r.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE
        || r.launchMode == ActivityInfo.LAUNCH_SINGLE_TASK) 
    // The activity being started is a single instance...  it always
    // gets launched into its own task.
    launchFlags |= Intent.FLAG_ACTIVITY_NEW_TASK;

// ......
if (r.resultTo != null && (launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK) != 0) 
    // For whatever reason this activity is being launched into a new
    // task...  yet the caller has requested a result back.  Well, that
    // is pretty messed up, so instead immediately send back a cancel
    // and let the new task continue launched as normal without a
    // dependency on its originator.
    Slog.w(TAG, "Activity is launching as a new task, so cancelling activity result.");
    r.resultTo.task.stack.sendActivityResultLocked(-1,
            r.resultTo, r.resultWho, r.requestCode,
        Activity.RESULT_CANCELED, null);
    r.resultTo = null;

但在 Android 5.x 中，更改如下：

final boolean launchSingleTop = r.launchMode == ActivityInfo.LAUNCH_SINGLE_TOP;
final boolean launchSingleInstance = r.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE;
final boolean launchSingleTask = r.launchMode == ActivityInfo.LAUNCH_SINGLE_TASK;
int launchFlags = intent.getFlags();
if ((launchFlags & Intent.FLAG_ACTIVITY_NEW_DOCUMENT) != 0 &&
        (launchSingleInstance || launchSingleTask)) 
    // We have a conflict between the Intent and the Activity manifest, manifest wins.
    Slog.i(TAG, "Ignoring FLAG_ACTIVITY_NEW_DOCUMENT, launchMode is " +
            "\"singleInstance\" or \"singleTask\"");
    launchFlags &=
            ~(Intent.FLAG_ACTIVITY_NEW_DOCUMENT | Intent.FLAG_ACTIVITY_MULTIPLE_TASK);
 else 
    switch (r.info.documentLaunchMode) 
        case ActivityInfo.DOCUMENT_LAUNCH_NONE:
            break;
        case ActivityInfo.DOCUMENT_LAUNCH_INTO_EXISTING:
            launchFlags |= Intent.FLAG_ACTIVITY_NEW_DOCUMENT;
            break;
        case ActivityInfo.DOCUMENT_LAUNCH_ALWAYS:
            launchFlags |= Intent.FLAG_ACTIVITY_NEW_DOCUMENT;
            break;
        case ActivityInfo.DOCUMENT_LAUNCH_NEVER:
            launchFlags &= ~Intent.FLAG_ACTIVITY_MULTIPLE_TASK;
            break;
    

final boolean launchTaskBehind = r.mLaunchTaskBehind
        && !launchSingleTask && !launchSingleInstance
        && (launchFlags & Intent.FLAG_ACTIVITY_NEW_DOCUMENT) != 0;
if (r.resultTo != null && (launchFlags & Intent.FLAG_ACTIVITY_NEW_TASK) != 0) 
    // For whatever reason this activity is being launched into a new
    // task...  yet the caller has requested a result back.  Well, that
    // is pretty messed up, so instead immediately send back a cancel
    // and let the new task continue launched as normal without a
    // dependency on its originator.
    Slog.w(TAG, "Activity is launching as a new task, so cancelling activity result.");
    r.resultTo.task.stack.sendActivityResultLocked(-1,
            r.resultTo, r.resultWho, r.requestCode,
            Activity.RESULT_CANCELED, null);
    r.resultTo = null;

这就是为什么 onActivityResult 可以在 Android 5.x 中运行，即使您将 launchMode 设置为 singleTask 或 singleInstance。

【参考方案3】：

@Peter Knego 怎么说

加

它似乎在 5.1 中工作，而不是在 4.4.4

表示 onActivityResult 触发

【讨论】：

是的，我还观察到它在 5.o 及更高版本中工作，而不是在 4.4.4 中

【参考方案4】：

澄清一些答案：

API 的

startActivityForResult() 与启动模式 singleTask 或 singleInstance 结合使用不起作用。 onActivityResult() 将立即被调用，结果代码为Activity.RESULT_CANCELED。

API 的 >= Android 5.x：

startActivityForResult() 有效，但启动模式singleTask 或singleInstance 基本上被忽略，这意味着活动被启动到同一个任务中并且没有创建新任务。

如果你想验证这个运行adb shell dumpsys activity activities。我只希望系统至少会向我显示一个警告。

这种变化也反映在@GGCoke 的代码位中有posted。

【参考方案5】：

我知道这已经很晚了，但您可以对 onNewIntent() 方法产生 OnActivityResult 效果，因为这是您的 singleTask 活动。