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。