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

巴特西

startActivityForResult中回调setResult注意事项

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