startActivityForResult中回调setResult注意事项

读 http://www.cnblogs.com/lijunamneg/archive/2013/02/05/2892616.html 有感

文中提出了一个核心问题：

Android activity的setResult()在什么时候调用？

他给出了答案：

activity返回result是在被finish的时候，也就是说调用setResult()方法必须在finish()之前。
那么如果在如下方法中调用setResult()也有可能不会返回成功： onPause()， onStop()， onDestroy(),
因为这些方法调用不一定是在finish之前的，当然在onCreate()就调用setResult肯定是在finish之前的

什么意思呢：

假设我们有MainActivity和SecondActivity来一次跳转。

package com.example.setresult;

import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;
import android.os.Build;

public class MainActivity extends ActionBarActivity {

    private final static String TAG = MainActivity.class.getSimpleName();

	final int   requestCode=1;
	Button b1;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        b1=(Button)findViewById(R.id.b1);
        b1.setOnClickListener(new OnClickListener() {

			@Override
			public void onClick(View v) {
				startActivityForResult(new Intent(MainActivity.this,SecondActivity.class), requestCode);

			}
		});
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent arg2) {
    	Log.d(TAG, "resultCode="+resultCode);
    	  switch (resultCode) {
          case RESULT_OK:
        	  Log.d(TAG, "ok");
              break;
      }
    	super.onActivityResult(requestCode, resultCode, arg2);
    }

    @Override
    protected void onRestart() {
  	  Log.d(TAG, "MainActivity onRestart");
    	super.onRestart();
    }
    @Override
    protected void onResume() {
    	 Log.d(TAG, "MainActivity onResume");
    	super.onResume();
    }
}

　　

package com.example.setresult;

import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.os.Build;

public class SecondActivity extends ActionBarActivity {
    private final static String TAG = SecondActivity.class.getSimpleName();

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_second);
		setResult(RESULT_OK);
	}

	@Override
	protected void onStop() {

	Log.d(TAG, "SecondActivity onStop");
		super.onStop();
	}
	@Override
	protected void onDestroy() {
		Log.d(TAG, "SecondActivity onDestroy");
		super.onDestroy();
	}
	@Override
	public void onBackPressed() {

		Log.d(TAG, "SecondActivity onBackPressed");
		super.onBackPressed();
	}
	@Override
	protected void onStart() {
		Log.d(TAG, "SecondActivity onStart");
		super.onStart();
	}
	@Override
	protected void onPause() {

		Log.d(TAG, "SecondActivity onPause");
		super.onPause();
	}
}

　　

07-30 20:15:37.291: D/SecondActivity(30684): SecondActivity onStart
07-30 20:15:39.151: D/SecondActivity(30684): SecondActivity onBackPressed

07-30 20:25:18.531: D/SecondActivity(32594): SecondActivity onPause

07-30 20:15:39.161: D/MainActivity(30684): resultCode=-1
07-30 20:15:39.161: D/MainActivity(30684): RESULT_OK
07-30 20:15:39.161: D/MainActivity(30684): MainActivity onRestart
07-30 20:15:39.161: D/MainActivity(30684): MainActivity onResume
07-30 20:15:39.501: D/SecondActivity(30684): SecondActivity onStop
07-30 20:15:39.501: D/SecondActivity(30684): SecondActivity onDestroy

当从SecondActivity按返回键的时候，发生以上日志。可以看见resultCode=-1是正确的

但是当你把

setResult(RESULT_OK);

这句话放到SecondActivity Onstop()中

就会发生以下日志：

07-30 20:19:31.521: D/SecondActivity(31785): SecondActivity onStart
07-30 20:19:35.031: D/SecondActivity(31785): SecondActivity onBackPressed

07-30 20:25:18.531: D/SecondActivity(32594): SecondActivity onPause

07-30 20:19:35.051: D/MainActivity(31785): resultCode=0
07-30 20:19:35.051: D/MainActivity(31785): MainActivity onRestart
07-30 20:19:35.051: D/MainActivity(31785): MainActivity onResume
07-30 20:19:35.381: D/SecondActivity(31785): SecondActivity onStop
07-30 20:19:35.381: D/SecondActivity(31785): SecondActivity onDestroy

resultCode=0 说明setResult没有成功

可见当onBackPressed事件发生后，activity会直接掉finish()方法，这时候resultCode就已经返回给前一个Activity了，所以就得到默认值resultCode=0

由此得出一个结论

setResult()调用必须要在OnPause()之前