startActivityForResult usage

startActivityForResult method is a method in android activity starts, this method takes two parameters, the first one is the Intent, the other is a request code, the request code is a unique value can be long.

This method can be destroyed after the event, it returns a result to the previous activity.

For example: A opened the event activity B, then B activity after the destruction, you can return a result to the activities A.

This time is necessary in the event A, the method used to open the activity startActivityForResult B

        button1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent("com.example.activitytest.ACTTON_START");
                startActivityForResult(intent,1);//打开活动B
            }
        });

In the results of the activity by the method B setResult set to return, setResult () accepts two parameters, the first one is active to return the processing result, and generally only used RESULT_OK RESULT_CANCELED, other data which is transmitted with the Intent to back .

        button2.setOnClickListener ( new new View.OnClickListener () { 
            @Override 
            public  void the onClick (View View) { 
                the Intent Intent = new new the Intent (); 
                intent.putExtra ( "data_return", "test"); // results to return 
                setResult (RESULT_OK, Intent); 
                Finish (); // destruction activity B 
            } 
        });

B is destroyed after the event, will be on a callback activity (ie activity A) of onActivityResult () method (in the event you want to get passed in the A result, we need to override this method).

   @Override   //                        请求码          处理结果          带返回数据的Intent                  
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        switch (requestCode){
            case 1 :
                if(resultCode == RESULT_OK){
                    String returnData = data.getStringExtra("data_return");
                    Log.d("MainActivity",returnData);
                }
                break;
                default:
        }
    }

So after the event B is destroyed, it will return to activities A, B data activity to get a return. However, if the user does not click on the activities defined in the B button button2, but press the Back button, this time also need to override onBackPressed activity of B () method.

            @Override
            public void onBackPressed() {
                Intent intent = new Intent();
                intent.putExtra("data_return","测试一下");
                setResult(RESULT_OK,intent);
                finish();
            }
        });