关于启动模式中的问题

startActivityForResult的问题

A,B,C的启动模式都是默认的

Activity A 启动了Activity B，Activity B又启动了C，A-->B-->C, 这种情况下，A启动B要求B返回result给A

    

   如上图所示，Intent设置了Intent.FLAG_ACTIVITY_FORWARD_RESULT标志，那么此时将会交由C向A setResult。为了避免冲突，B启动C时不得指定resultRecord>=0。

        ActivityRecord sourceRecord = null;
        ActivityRecord resultRecord = null;
        if (resultTo != null) {
            int index = indexOfTokenLocked(resultTo);
            if (DEBUG_RESULTS) Slog.v(
                TAG, "Sending result to " + resultTo + " (index " + index + ")");
            if (index >= 0) {
                sourceRecord = (ActivityRecord)mHistory.get(index);
                if (requestCode >= 0 && !sourceRecord.finishing) {
                    resultRecord = sourceRecord;
                }
            }
        }

        int launchFlags = intent.getFlags();

        if ((launchFlags&Intent.FLAG_ACTIVITY_FORWARD_RESULT) != 0
                && sourceRecord != null) {
            // Transfer the result target from the source activity to the new
            // one being started, including any failures.
            if (requestCode >= 0) {
                return START_FORWARD_AND_REQUEST_CONFLICT;
            }
            resultRecord = sourceRecord.resultTo;
            resultWho = sourceRecord.resultWho;
            requestCode = sourceRecord.requestCode;
            sourceRecord.resultTo = null;
            if (resultRecord != null) {
                resultRecord.removeResultsLocked(
                    sourceRecord, resultWho, requestCode);
            }

A-->B

如果A和B不在同一个task中，那么startActivityForResult將返回RESULT_CANCELED

 如果启动的activity需要新的task，那么新启动的activity将会与其caller断开依赖关系，这个关系主要是指result反馈，A-->B,如果A是通过startActivityForResult()请求启动的，并且requestCode >=0,那么如果B是在新的task中，那么B在finish的时候将不再向A反馈result，而是在启动过程中就会向A反馈一个RESULT_CANCELED。

        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.");
            sendActivityResultLocked(-1,
                    r.resultTo, r.resultWho, r.requestCode,
                Activity.RESULT_CANCELED, null);
            r.resultTo = null;
        }

摘自http://blog.csdn.net/windskier/article/details/7096521