onActivityResult With launchMode="singleTask"?

Question

When you try to startActivityForResult for Activity that has launchMode="singleTask"; it will not return any values with onActivityResult,and when you set launchMode="standard"; everything works fine, but the system requirements says this Activity must be singleTask, is there anyway to solve this?

Answer 1

The docs of the startActivityForResult say:

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. 

It seems there is no way to get around this.

If you are the developer of called Activity, then you can have it send a broadcast when some result is available. The calling Activity can then list to this broadcasts.

Answer 2

The answer shows in function startActivityUncheckedLocked of class ActivityStackSupervisor. Before Android 5.x, when starting an activity, it will check launchMode first and add FLAG_ACTIVITY_NEW_TASK to launchFlags if launchMode is singleTask or singleInstance. If the activity's launchFlags contains FLAG_ACTIVITY_NEW_TASK, it will send back a cancel immediately and let the new task continue launched as normal without a dependency on its originator.

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; } 

But in Android 5.x, this was changed as below:

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; } 

That's why onActivityResult works in Android 5.x even you set launchMode to singleTask or singleInstance.