一个关于startActivityForResult的小问题

之前开发需求时,需要调用系统相机拍照.并将拍照照片上传服务端.但拍照后死活获取不到返回的result.

@Overridepublic void onActivityResult(int requestCode, int resultCode, Intent data) {if (requestCode == CAMERA_REQUEST_CODE && resultCode == Activity.RESULT_OK) {if (mCurrentCameraFile != null && mCurrentCameraFile.exists()) {....Log.v( TAG,"onActivityResult get pic success ");//通知MediaScan进行扫描添加数据库BitmapUtils.notifyAddPictureToSDCard(mContext, mCurrentCameraFile);}}}

怎么都不打印日志:onActivityResult get pic success.这里我打印日志比较片面,仅打印了成功的日志....

为了这个破问题折腾了好几个小时.太菜了呃...

         首先上传调用相机的代码

<span style="white-space:pre"></span>mCurrentCameraFile = Utils.getOutputMediaFile();Intent cameraIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);        Uri outputFileUri = Uri.fromFile(mCurrentCameraFile);        cameraIntent.putExtra(MediaStore.EXTRA_OUTPUT, outputFileUri);cameraIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);mParentFragment.startActivityForResult(cameraIntent, CAMERA_REQUEST_CODE);

        无意中发现,只要去掉cameraIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK)这一行,就立马可以得到正确的ActivityResult了.为啥啊?不就是新起一个栈来启动相机吗?

直接看看startActivity的源码怎么对这个FLAG_ACTIVITY_NEW_TASK怎么处理的吧,源码位于(android4.4.2)frameworks\base\services\java\com\android\server\am\ActivityStackSupervisor.java

final int startActivityUncheckedLocked(ActivityRecord r,            ActivityRecord sourceRecord, int startFlags, boolean doResume,            Bundle options) {        final Intent intent = r.intent;        final int callingUid = r.launchedFromUid;        int launchFlags = intent.getFlags();        ...        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);                <span style="color:#ff0000;">launchFlags |= Intent.FLAG_ACTIVITY_NEW_TASK;</span>            }        } 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.            <span style="color:#ff0000;">launchFlags |= Intent.FLAG_ACTIVITY_NEW_TASK;</span>        } 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.            <span style="color:#ff0000;">launchFlags |= Intent.FLAG_ACTIVITY_NEW_TASK;</span>        }        ActivityInfo newTaskInfo = null;        Intent newTaskIntent = null;        final ActivityStack sourceStack;        if (sourceRecord != null) {            if (sourceRecord.finishing) {                // If the source is finishing, we can't further count it as our source.  This                // is because the task it is associated with may now be empty and on its way out,                // so we don't want to blindly throw it in to that task.  Instead we will take                // the NEW_TASK flow and try to find a task for it. But save the task information                // so it can be used when creating the new task.                if ((launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK) == 0) {                    Slog.w(TAG, "startActivity called from finishing " + sourceRecord                            + "; forcing " + "Intent.FLAG_ACTIVITY_NEW_TASK for: " + intent);                    <span style="color:#ff0000;">launchFlags |= Intent.FLAG_ACTIVITY_NEW_TASK;</span>                    newTaskInfo = sourceRecord.info;                    newTaskIntent = sourceRecord.task.intent;                }                sourceRecord = null;                sourceStack = null;            } else {                sourceStack = sourceRecord.task.stack;            }        } else {            sourceStack = null;        }        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.");            <span style="color:#ff0000;">r.resultTo.task.stack.sendActivityResultLocked(-1,                    r.resultTo, r.resultWho, r.requestCode,                Activity.RESULT_CANCELED, null);</span>            r.resultTo = null;        }        .....        if (newTask) {            EventLog.writeEvent(EventLogTags.AM_CREATE_TASK, r.userId, r.task.taskId);        }        ActivityStack.logStartActivity(EventLogTags.AM_CREATE_ACTIVITY, r, r.task);        targetStack.mLastPausedActivity = null;        <span style="color:#ff0000;">targetStack.startActivityLocked(r, newTask, doResume, keepCurTransition, options);</span>        mService.setFocusedActivityLocked(r);        return ActivityManager.START_SUCCESS;    }

上面的startActivityUncheckedLocked()方法我主要截取了前面对FLAG_ACTIVITY_NEW_TASK的处理.

1.对于一下场景,都会对intent的FLAG_ACTIVITY_NEW_TASK标志位置1.

(1)sourceRecord为空,即执行startActivity的哪个ActvityRecord为空;

                (2)sourceRecord.launchMode为ActivityInfo.LAUNCH_SINGLE_INSTANCE;

                (3)待启动的新ActivityRecord的launchMode为LAUNCH_SINGLE_INSTANCE或者LAUNCH_SINGLE_TASK;

2.若需要返回result,且intent的FLAG_ACTIVITY_NEW_TASK标志位为1,则首先给ResultToActivity一个RESULT_CANCELED(即-1)结果.这个逻辑比较简单,直接让ActivityThread来分发onActivityResult()

        3.初始化好目标targetStack后,继续执行startActivity,具体可以参见老罗的android之旅Android应用程序内部启动Activity过程（startActivity）的源代码分析.

通过上面startActivityUncheckedLocked()方法的分析,直到只要设置了FLAG_ACTIVITY_NEW_TASK,源Activity就会收到RESULT_CANCELED结果回调.下面用demo测试下.

@Overrideprotected void onActivityResult(int requestCode, int resultCode, Intent data) {Log.e("onActivityResult ", "requestCode:" + requestCode + "resultCode:" + resultCode + ",data" + data);Toast.makeText(this, "onActivityResult resultCode " + resultCode, Toast.LENGTH_SHORT).show();super.onActivityResult(requestCode, resultCode, data);}public static final int CAMERA_REQUEST_CODE = 111;@Overridepublic void onClick(View v) {switch (v.getId()) {case R.id.btn1:Intent intent = getContentProviderActivityIntent();intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);if (intent != null) {startActivityForResult(intent, CAMERA_REQUEST_CODE);}break;case R.id.btn2:Intent intent1 = getContentProviderActivityIntent();if (intent1 != null) {startActivityForResult(intent1, CAMERA_REQUEST_CODE);}break;}}private File mCurrentCameraFile;public Intent getContentProviderActivityIntent() {mCurrentCameraFile = getOutputMediaFile();if (mCurrentCameraFile != null) {return getCameraAppIntent(mCurrentCameraFile);} else {return null;}}public static Intent getCameraAppIntent(File outFile) {Intent cameraIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);        Uri outputFileUri = Uri.fromFile(outFile);        cameraIntent.putExtra(MediaStore.EXTRA_OUTPUT, outputFileUri);return cameraIntent;}public static File getOutputMediaFile() {File mediaStorageDir = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DCIM), "Camera");if (!mediaStorageDir.exists()) {if (!mediaStorageDir.mkdirs()) {return null;}}// Create a media file nameString timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss", Locale.CHINA).format(new Date());File mediaFile = new File(mediaStorageDir.getPath() + File.separator + "IMG_" + timeStamp + ".jpg");return mediaFile;}

两个按钮,分别为添加和不添加FLAG_ACTIVITY_NEW_TASK标志.打印日志如下:

btn1:在相机页面还没起来前就打印了:12-31 09:51:39.566: E/onActivityResult(20938): requestCode:111resultCode:0,datanull

btn2:在相机页面结束后才打印了:12-31 09:53:01.880: E/onActivityResult(20938): requestCode:111resultCode:-1,datanull

就这样了,startActivityForResult时不能设置FLAG_ACTIVITY_NEW_TASK标志