Startactivityforresult does not work

Use startactivityforresult to call Activity B from activity,

However, when startactivityforresult is called, the protected void onactivityresult (INT requestcode, int resultcode, intent data) in a is immediately called ),

Read the instructions:

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.

In this case, B cannot be a single example, that is, launchmode cannot be set as follows:

Android: launchmode = "singleinstance"

Remove the above settings in B, but the same problem still exists,

You can run normally only when the preceding settings are removed from.

Therefore, the singinstance activity can only transmit data in other ways.