Android开发之一个未解决的bug

使用Activity之间传递数据的时候，出现了一个bug，但是没有找到哪里出错了。

把代码和log都记录下来，以后研究

代码：

MainActivity.class

 package com.example.caradviser;

 import java.util.ArrayList;
 import java.util.List;

 import android.app.Activity;
 import android.content.Intent;
 import android.net.Uri;
 import android.os.Bundle;
 import android.util.Log;
 import android.view.View;
 import android.view.Window;
 import android.widget.Spinner;
 import android.widget.TextView;
 import android.widget.Toast;

 public class MainActivity extends Activity {

     private static final String TAG = "com.example.caradviser";
     TextView showBackText;

     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         requestWindowFeature(Window.FEATURE_NO_TITLE);
         setContentView(R.layout.activity_main);
         showBackText=(TextView) findViewById(R.id.backMainActivity);
     }

     @Override
     protected void onActivityResult(int requestCode, int resultCode, Intent intent) {
         super.onActivityResult(requestCode, resultCode, intent);

         switch (requestCode) {
         case 123123:
             if (resultCode==RESULT_OK) {
                 if (intent==null||"".equals(intent)) {
                     Toast.makeText(MainActivity.this, "获取到的数据为空", Toast.LENGTH_SHORT).show();
                 }else {
                     String getData = intent.getStringExtra("data_return");
                     showBackText.setText(intent.getStringExtra("data_return"));
                 }
             }
             break;

         default:
             break;
         }
     }

     public void toAnotherActivity3(View v){
         String data ="Hello,这是传递的数据";
         Intent intent = new Intent(MainActivity.this,ThreeActivity.class);
         intent.putExtra("haha", data);
         startActivityForResult(intent, 123123);
     }
 }

ThreeActivity.class

 package com.example.caradviser;

 import android.app.Activity;
 import android.content.Intent;
 import android.os.Bundle;
 import android.text.TextUtils;
 import android.view.View;
 import android.view.View.OnClickListener;
 import android.view.Window;
 import android.widget.Button;
 import android.widget.TextView;
 import android.widget.Toast;

 public class ThreeActivity extends Activity {

     private Button backToMainActivity;
     private String data;
     private TextView textView;

     @Override
     protected void onCreate(Bundle savedInstanceState) {
         // TODO Auto-generated method stub
         super.onCreate(savedInstanceState);
         requestWindowFeature(Window.FEATURE_NO_TITLE);
         setContentView(R.layout.three_layout);

         Intent intent = getIntent();
         data = intent.getStringExtra("haha");

         textView = (TextView) findViewById(R.id.showText);

         if (TextUtils.isEmpty(data)) {
             Toast.makeText(ThreeActivity.this, "没有接收到其他activity的数据", Toast.LENGTH_SHORT).show();
         }else {
             textView.setText(data);
         }

         backToMainActivity = (Button) findViewById(R.id.backMainActivity);
         backToMainActivity.setOnClickListener(new OnClickListener() {

             @Override
             public void onClick(View v) {
                 // TODO Auto-generated method stub
                 Intent intent = new Intent();
                 String data3= "将要返回到MainActivity";
                 intent.putExtra("data_return", data3);
                 setResult(RESULT_OK,intent);
                 finish();
             }
         });
     }

 }

Log

 10-12 16:22:02.304: E/AndroidRuntime(16265): FATAL EXCEPTION: main
 10-12 16:22:02.304: E/AndroidRuntime(16265): Process: com.example.caradviser, PID: 16265
 10-12 16:22:02.304: E/AndroidRuntime(16265): java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=123123, result=-1, data=Intent { (has extras) }} to activity {com.example.caradviser/com.example.caradviser.MainActivity}: java.lang.NullPointerException
 10-12 16:22:02.304: E/AndroidRuntime(16265):     at android.app.ActivityThread.deliverResults(ActivityThread.java:3375)
 10-12 16:22:02.304: E/AndroidRuntime(16265):     at android.app.ActivityThread.handleSendResult(ActivityThread.java:3418)
 10-12 16:22:02.304: E/AndroidRuntime(16265):     at android.app.ActivityThread.access$1300(ActivityThread.java:141)
 10-12 16:22:02.304: E/AndroidRuntime(16265):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1261)
 10-12 16:22:02.304: E/AndroidRuntime(16265):     at android.os.Handler.dispatchMessage(Handler.java:102)
 10-12 16:22:02.304: E/AndroidRuntime(16265):     at android.os.Looper.loop(Looper.java:136)
 10-12 16:22:02.304: E/AndroidRuntime(16265):     at android.app.ActivityThread.main(ActivityThread.java:5072)
 10-12 16:22:02.304: E/AndroidRuntime(16265):     at java.lang.reflect.Method.invokeNative(Native Method)
 10-12 16:22:02.304: E/AndroidRuntime(16265):     at java.lang.reflect.Method.invoke(Method.java:515)
 10-12 16:22:02.304: E/AndroidRuntime(16265):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
 10-12 16:22:02.304: E/AndroidRuntime(16265):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:609)
 10-12 16:22:02.304: E/AndroidRuntime(16265):     at dalvik.system.NativeStart.main(Native Method)
 10-12 16:22:02.304: E/AndroidRuntime(16265): Caused by: java.lang.NullPointerException
 10-12 16:22:02.304: E/AndroidRuntime(16265):     at com.example.caradviser.MainActivity.onActivityResult(MainActivity.java:42)
 10-12 16:22:02.304: E/AndroidRuntime(16265):     at android.app.Activity.dispatchActivityResult(Activity.java:5441)
 10-12 16:22:02.304: E/AndroidRuntime(16265):     at android.app.ActivityThread.deliverResults(ActivityThread.java:3371)
 10-12 16:22:02.304: E/AndroidRuntime(16265):     ... 11 more

具体什么原因造成的，目前我还无法确定，等待能力提高以后，回头看看这个问题。