Question

我有一个Android应用程序，它包含两个类JSONTransmitter类和MainActivity类，此应用程序的目标是发布并从php文件获取响应并在小部件上显示此响应。

我对MainActivity类的onResponse方法有一个小问题 - 当我使用button.setText（“”）时它不起作用，如果它不起作用！

JSONTransmitter类

public class JSONTransmitter extends AsyncTask<JSONObject, Void, String>
{
HttpResponse response; 
String url = "http://192.168.1.13:89/Derdeery/b.php";
private AsyncCallback asyncCallback;
public static interface AsyncCallback {
void onResponse(String res);

}
public JSONTransmitter(Context context) 
{
    // attach the callback to any context
    asyncCallback = (AsyncCallback) context;
}
protected String doInBackground(JSONObject... data) { 
     JSONObject json = data[0]; 

     HttpClient client = new DefaultHttpClient(); 
     HttpConnectionParams.setConnectionTimeout(client.getParams(), 100000); 
     StrictMode.setThreadPolicy(new StrictMode.ThreadPolicy.Builder().permitNetwork().build()); 
     JSONObject jsonResponse = null; 

     HttpPost post = new HttpPost(url); 

     // initialize a return string 
     String resFromServer = ""; 

     try { 
     StringEntity se = new StringEntity("json="+json.toString()); 

     post.addHeader("content-type", "application/x-www-form-urlencoded"); 
     post.setEntity(se); 

     HttpResponse response; 
     response = client.execute(post); 

     // when you can get the json, you modify the return string 
     resFromServer = org.apache.http.util.EntityUtils.toString(response.getEntity()); 

     Log.i("Response from server", resFromServer); 


     } 
     catch (Exception e) 
     { e.printStackTrace();} 

     // now you can return a string 
     return resFromServer; 

}

MainActivity类

public class MainActivity extends Activity implements JSONTransmitter.AsyncCallback {


    private Button b ; 

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

     Button   b = (Button)findViewById(R.id.button1) ;  

        b.setOnClickListener(new OnClickListener() { 
             @Override 
             public void onClick(View view) { 
                mymethod() ;


                } 
             });      
    }

    public void mymethod()
    {
         try {

            TelephonyManager tm = (TelephonyManager)getSystemService(TELEPHONY_SERVICE); 
            String  mPhoneNumber = tm.getLine1Number();  

             JSONObject toSend = new JSONObject();
             toSend.put("msg", mPhoneNumber );



             new JSONTransmitter(this).execute(new JSONObject[] {toSend});

         } catch (JSONException e) {
             e.printStackTrace();
         }




    }

    @Override
    public  void onResponse(String res) 
    {
        // TODO Auto-generated method stub
        Log.v("From_MainActivity", "AsyncTask returns this: "+res);
            b.setText(res);
    }


   }

xml文件

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity" >

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:text="Button" />


</RelativeLayout>

将JSONTransmitter类更新为以下

public class JSONTransmitter extends AsyncTask<JSONObject, Void, String> {
HttpResponse response; 
String url = "http://192.168.1.20:89/Derdeery/b.php";
private AsyncCallback asyncCallback;

public static interface AsyncCallback {
    void onResponse(String res);

}
public JSONTransmitter(Context context) 
{
    // attach the callback to any context
    asyncCallback = (AsyncCallback) context;
}
@Override
protected void onPostExecute(String result) {
  super.onPostExecute(result);
  asyncCallback.onResponse(result);
}
protected String doInBackground(JSONObject... data) { 
     JSONObject json = data[0]; 

     HttpClient client = new DefaultHttpClient(); 
     HttpConnectionParams.setConnectionTimeout(client.getParams(), 100000); 
     StrictMode.setThreadPolicy(new StrictMode.ThreadPolicy.Builder().permitNetwork().build()); 
     JSONObject jsonResponse = null; 

     HttpPost post = new HttpPost(url); 

     // initialize a return string 
     String resFromServer = ""; 

     try { 
     StringEntity se = new StringEntity("json="+json.toString()); 

     post.addHeader("content-type", "application/x-www-form-urlencoded"); 
     post.setEntity(se); 

     HttpResponse response; 
     response = client.execute(post); 

     // when you can get the json, you modify the return string 
     resFromServer = org.apache.http.util.EntityUtils.toString(response.getEntity()); 

     Log.i("Response from server", resFromServer); 


     } 
     catch (Exception e) 
     { e.printStackTrace();} 

     // now you can return a string 
     return resFromServer; 

}

我的应用程序崩溃，我收到此日志错误

 01-18 06:30:07.721: E/AndroidRuntime(810): FATAL EXCEPTION: main
01-18 06:30:07.721: E/AndroidRuntime(810): java.lang.NullPointerException
01-18 06:30:07.721: E/AndroidRuntime(810):  at com.coffeecodes.coffecodesdoodle.MainActivity.onResponse(MainActivity.java:66)
01-18 06:30:07.721: E/AndroidRuntime(810):  at com.coffeecodes.coffecodesdoodle.JSONTransmitter.onPostExecute(JSONTransmitter.java:48)
01-18 06:30:07.721: E/AndroidRuntime(810):  at com.coffeecodes.coffecodesdoodle.JSONTransmitter.onPostExecute(JSONTransmitter.java:1)
01-18 06:30:07.721: E/AndroidRuntime(810):  at android.os.AsyncTask.finish(AsyncTask.java:631)
01-18 06:30:07.721: E/AndroidRuntime(810):  at android.os.AsyncTask.access$600(AsyncTask.java:177)
01-18 06:30:07.721: E/AndroidRuntime(810):  at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
01-18 06:30:07.721: E/AndroidRuntime(810):  at android.os.Handler.dispatchMessage(Handler.java:99)
01-18 06:30:07.721: E/AndroidRuntime(810):  at android.os.Looper.loop(Looper.java:137)
01-18 06:30:07.721: E/AndroidRuntime(810):  at android.app.ActivityThread.main(ActivityThread.java:5039)
01-18 06:30:07.721: E/AndroidRuntime(810):  at java.lang.reflect.Method.invokeNative(Native Method)
01-18 06:30:07.721: E/AndroidRuntime(810):  at java.lang.reflect.Method.invoke(Method.java:511)
01-18 06:30:07.721: E/AndroidRuntime(810):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
01-18 06:30:07.721: E/AndroidRuntime(810):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
01-18 06:30:07.721: E/AndroidRuntime(810):  at dalvik.system.NativeStart.main(Native Method)
01-18 06:30:12.950: I/Process(810): Sending signal. PID: 810 SIG: 9

Answer 1

MainActivity类的onResponse方法 - 当我使用button.setText（“”）时它不起作用

要使其工作，请致电asyncCallback.onResponse()中的onPostExecute：

   @Override
    protected void onPostExecute(String result) {
      super.onPostExecute(result);
      asyncCallback.onResponse(result);
    }

覆盖onPostExecute中的JSONTransmitter并将result字符串作为参数传递给onResponse方法。

当我在其中使用Button.setText（“”）时，方法不起作用

1 个答案: