Android LaunchMode and StartActivityForResult冲突问题

问题描述：

同时使用FLAG_AVTIVITY_NEW_TASK和StartActivityForResult时，在新activity启动之前，直接调用了老activity的onActivityResult。

问题原因：

http://blog.csdn.net/dliyuedong/article/details/47172143 

android4.0+已经占据目前主流android系统版本了，在5.0版本发布后，android的LaunchMode与StartActivityForResult的关系发生了一些改变。

两个Activity，A和B，现在由A页面跳转到B页面，看一下LaunchMode与StartActivityForResult之间的关系：

android5.0之前

	stand	singleTop	singleTask	singleInstance
stand	√	√	x	x
singleTop	√	√	x	x
singleTask	√	√	x	x
singleInstance	x	x	x	x

android5.0之后

	stand	singleTop	singleTask	singleInstance
stand	√	√	√	√
singleTop	√	√	√	√
singleTask	√	√	√	√
singleInstance	√	√	√	√

为什么会是这样的呢？

ActivityStackSupervisor类中的startActivityUncheckedLocked方法在5.0中进行了修改。在5.0之前，当启动一个Activity时，系统将首先检查Activity的launchMode，如果为A页面设置为SingleInstance或者B页面设置为singleTask或者singleInstance,则会在LaunchFlags中加入FLAG_ACTIVITY_NEW_TASK标志，而如果含有FLAG_ACTIVITY_NEW_TASK标志的话，onActivityResult将会立即接收到一个cancle的信息。

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; } 

在5.0(含)之后的系统中，对此方法进行了修改：

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; } 

这就解析了为什么5.0(含)之后的系统即便启动的页面设置launchMode为singleTask或singleInstance，onActivityResult依旧可以正常工作。

 

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