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我们使用Intent可以将数据从一个Activity传递到下一个Activity，同样，在Android中我们可以将数据从一个Activity返回给前一个Activity。
参考API Demo示例：
1. 定义父Activity，ReceiveResult.java。在这个Activity中我们通过startActivityForResult(intent, GET_CODE)启动子Activity。
Java代码
package com.example.android.apis.app;import java.util.Map;import com.example.android.apis.R;import android.app.Activity;
import android.content.Intent;
import android.text.Editable;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;import java.util.Map;public class ReceiveResult extends Activity {@Overrideprotected void onCreate(Bundle savedInstanceState) {// Be sure to call the super class.super.onCreate(savedInstanceState);// See assets/res/any/layout/hello_world.xml for this// view layout definition, which is being set here as// the content of our screen.setContentView(R.layout.receive_result);// Retrieve the TextView widget that will display results.mResults = (TextView)findViewById(R.id.results);// This allows us to later extend the text buffer.mResults.setText(mResults.getText(), TextView.BufferType.EDITABLE);// Watch for button clicks.Button getButton = (Button)findViewById(R.id.get);getButton.setOnClickListener(mGetListener);}@Overrideprotected void onActivityResult(int requestCode, int resultCode,Intent data) {// You can use the requestCode to select between multiple child// activities you may have started. Here there is only one thing// we launch.if (requestCode == GET_CODE) {// We will be adding to our text.Editable text = (Editable)mResults.getText();// This is a standard resultCode that is sent back if the// activity doesn't supply an explicit result. It will also// be returned if the activity failed to launch.if (resultCode == RESULT_CANCELED) {text.append("(cancelled)");// Our protocol with the sending activity is that it will send// text in 'data' as its result.} else {text.append("(okay ");text.append(Integer.toString(resultCode));text.append(") ");if (data != null) {text.append(data.getAction());}}text.append("\n");}}// Definition of the one requestCode we use for receiving resuls.static final private int GET_CODE = 0;private OnClickListener mGetListener = new OnClickListener() {public void onClick(View v) {// Start the activity whose result we want to retrieve. The// result will come back with request code GET_CODE.Intent intent = new Intent(ReceiveResult.this, SendResult.class);startActivityForResult(intent, GET_CODE);}};private TextView mResults;
}
我们需要为startActivityForResult传递一个Intent和一个请求码。
Intent决定启动哪个Activity。请求码是对子Activity标记的唯一ID。假如从一个父Activity中可能启动的子Activity有多个，那么通过请求码我们就可以知道是从哪个子Activity返回的。
2. 定义子Activity，SendResult.java。在这个Activity中我们通过setResult(RESULT_OK, (new Intent()).setAction("Corky!"))将结果返回给父Activity。
Java代码
package com.example.android.apis.app;import com.example.android.apis.R;import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;public class SendResult extends Activity
{@Overrideprotected void onCreate(Bundle savedInstanceState){// Be sure to call the super class.super.onCreate(savedInstanceState);// See assets/res/any/layout/hello_world.xml for this// view layout definition, which is being set here as// the content of our screen.setContentView(R.layout.send_result);// Watch for button clicks.Button button = (Button)findViewById(R.id.corky);button.setOnClickListener(mCorkyListener);button = (Button)findViewById(R.id.violet);button.setOnClickListener(mVioletListener);}private OnClickListener mCorkyListener = new OnClickListener(){public void onClick(View v){// To send a result, simply call setResult() before your// activity is finished.setResult(RESULT_OK, (new Intent()).setAction("Corky!"));finish();}};private OnClickListener mVioletListener = new OnClickListener(){public void onClick(View v){// To send a result, simply call setResult() before your// activity is finished.setResult(RESULT_OK, (new Intent()).setAction("Violet!"));finish();}};
}
在调用finish()之前，要先调用setResult方法，将结果码和数据返回给父Activity。在android.app.Activity中定义两个标准结果码，RESULT_OK和RESULT_CANCELED。
如果子Activity启动失败或者没有显式的在setResult()中设置结果码，子Activity会默认返回RESULT_CANCELED。
3. 在父Activity中，我们重写onActivityResult(int requestCode, int resultCode, Intent data)方法，接收子Activity返回的数据。参考1中的代码。
请求码（requestCode）：通过它我们可以对多个子Activity进行处理。
结果码（resultCode）：通过它我们可以判断子Activity的处理结果，对不同的结果码进行相应的操作。
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