Facebook AsyncTask实现

我的代码如下。我在实现异步任务时遇到了麻烦，而针对异步任务的android文档对我来说有点令人困惑。任何人都可以用清晰的步骤向我解释它吗？Facebook AsyncTask实现

这里是我的代码：

package com.sara.facebookappl; 

import java.io.IOException; 
import java.net.MalformedURLException; 

import org.json.JSONException; 
import org.json.JSONObject; 
import android.app.Activity; 
import android.app.ProgressDialog; 
import android.content.Intent; 
import android.content.SharedPreferences; 
import android.content.SharedPreferences.Editor; 
import android.os.AsyncTask; 
import android.os.Bundle; 
import android.os.Looper; 
import android.view.Menu; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.widget.Button; 
import android.widget.ImageView; 
import android.widget.TextView; 
import android.widget.Toast; 

import com.facebook.android.DialogError; 
import com.facebook.android.Facebook; 
import com.facebook.android.Facebook.DialogListener; 
import com.facebook.android.FacebookError; 
import com.facebook.android.Util; 

public class MainActivity extends Activity implements OnClickListener, DialogListener { 

Facebook fb; 
ImageView button; 
private SharedPreferences sp; 
TextView welcome; 
Button post; 

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

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

    String APP_ID = getString(R.string.APP_ID); 
    fb= new Facebook(APP_ID); 

    Looper.prepare(); 
    new PostTask().execute(fb); 
    Looper.loop(); 

    sp =getPreferences(MODE_PRIVATE); 
    String access_token=sp.getString("access_token", null); 
    long expires=sp.getLong("access_expires", 0); 

    if (access_token !=null) { 
     fb.setAccessToken(access_token); 
    } 
    if(expires !=0) { 
     fb.setAccessExpires(expires); 
    } 


    button=(ImageView)findViewById(R.id.login); 
    button.setOnClickListener((OnClickListener) this); 
    updateButtonImage(); 

} 

private class PostTask extends AsyncTask<Facebook, Integer, String> { 

    ProgressDialog dialog; 

    protected void onPreExecute() { 
     dialog = new ProgressDialog(MainActivity.this); 
     dialog.setProgress(ProgressDialog.STYLE_HORIZONTAL); 
     dialog.setMax(100); 
     dialog.show(); 


    } 

    @SuppressWarnings("deprecation") 
    @Override 
    protected String doInBackground(Facebook... params) { 
     if (fb.isSessionValid()) { 
      button.setImageResource(R.drawable.com_facebook_loginbutton_blue); 
      // ^logout button 

     JSONObject obj=null; 

     try { 
     String jsonUser= fb.request("me"); 
     obj = Util.parseJson(jsonUser); 
     String name = obj.optString("name"); 
     welcome.setText("Welcome, " + name); 
     }catch(FacebookError e) { 
      e.printStackTrace(); 

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

     }else { 
      post.setVisibility(Button.VISIBLE); 
      button.setImageResource(R.drawable.com_facebook_loginbutton_blue); 
     } 
     return null; 
    } 
} 

protected void onProgressUpdated(Integer...progress) { 

} 

@SuppressWarnings("deprecation") 
protected void onPostExecute(Facebook result) { 

     // ^logout button 
    try {JSONObject obj=null; 
    String jsonUser= fb.request("me"); 
    obj = Util.parseJson(jsonUser); 
    String name = obj.optString("name"); 
    welcome.setText("Welcome, " + name);} 
    catch(FacebookError e) { 
     e.printStackTrace(); 

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


private void updateButtonImage() { 
    // TODO Auto-generated method stub 

    post.setVisibility(Button.VISIBLE); 
    button.setImageResource(R.drawable.com_facebook_loginbutton_blue); 
    //logout button 


} 

@SuppressWarnings("deprecation") 
public void buttonClicks(View v) { 
    switch (v.getId()) { 
     case R.id.button1: 
      //post 

      Bundle params= new Bundle(); 

      params.putString("name", "User X"); 
      params.putString("caption", "Rating"); 
      params.putString("description", "User X Rated"); 
      params.putString("link", "http://..."); 



      fb.dialog(MainActivity.this, "feed", params, new Facebook.DialogListener() { 

       @Override 
       public void onFacebookError(FacebookError e) { 
        // TODO Auto-generated method stub 

       } 

       @Override 
       public void onError(DialogError e) { 
        // TODO Auto-generated method stub 

       } 

       @Override 
       public void onComplete(Bundle values) { 
        // TODO Auto-generated method stub 

       } 

       @Override 
       public void onCancel() { 
        // TODO Auto-generated method stub 

       } 
      }); 
      break; 
    } 
} 
@SuppressWarnings("deprecation") 
public void onClick(View v) { 
    if(fb.isSessionValid()) { 

     try { 
     fb.logout(getApplicationContext()); 
     updateButtonImage(); 
     //button will close our our session 
    }catch(MalformedURLException e) { 
     e.printStackTrace(); 
    } catch(IOException e) { 
     e.printStackTrace(); 
    } 
}else{ 
     //login into facebook 
     fb.authorize(MainActivity.this, new String[] {"email"}, new Facebook.DialogListener() { 

      @Override 
      public void onFacebookError(FacebookError e) { 
       // TODO Auto-generated method stub 
       Toast.makeText(MainActivity.this, "fbError", Toast.LENGTH_SHORT).show(); 
      } 

      @Override 
      public void onError(DialogError e) { 
       // TODO Auto-generated method stub 
       Toast.makeText(MainActivity.this, "onError", Toast.LENGTH_SHORT).show(); 
      } 

      @Override 
      public void onComplete(Bundle values) { 
       // TODO Auto-generated method stub 
       Editor editor=sp.edit(); 
       editor.putString("access_token", fb.getAccessToken()); 
       editor.putLong("access_expires", fb.getAccessExpires()); 
       editor.commit(); 
       updateButtonImage(); 
      } 

      @Override 
      public void onCancel() { 
       // TODO Auto-generated method stub 
       Toast.makeText(MainActivity.this, "onCancel", Toast.LENGTH_SHORT).show(); 
      } 
     }); 

     } 
} 


@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
    // Inflate the menu; this adds items to the action bar if it is present. 
    getMenuInflater().inflate(R.menu.activity_main, menu); 
    return true; 
} 

@SuppressWarnings("deprecation") 
@Override 
protected void onActivityResult(int requestCode, int resultCode, Intent data) { 
    super.onActivityResult(requestCode, resultCode, data); 
    fb.authorizeCallback(requestCode, resultCode, data); 
} 

@Override 
public void onComplete(Bundle values) { 
    // TODO Auto-generated method stub 

} 

@Override 
public void onFacebookError(FacebookError e) { 
    // TODO Auto-generated method stub 

} 

@Override 
public void onError(DialogError e) { 
    // TODO Auto-generated method stub 

} 

@Override 
public void onCancel() { 
    // TODO Auto-generated method stub 

}

}

而这里的logcat的错误：

12-17 19:24:04.886: E/AndroidRuntime(862): FATAL EXCEPTION: AsyncTask #1 
12-17 19:24:04.886: E/AndroidRuntime(862): java.lang.RuntimeException: An error occured  while executing doInBackground() 
12-17 19:24:04.886: E/AndroidRuntime(862): at  android.os.AsyncTask$3.done(AsyncTask.java:299) 
12-17 19:24:04.886: E/AndroidRuntime(862): at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:352) 
12-17 19:24:04.886: E/AndroidRuntime(862): at java.util.concurrent.FutureTask.setException(FutureTask.java:219) 
12-17 19:24:04.886: E/AndroidRuntime(862): at java.util.concurrent.FutureTask.run(FutureTask.java:239) 
12-17 19:24:04.886: E/AndroidRuntime(862): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230) 
12-17 19:24:04.886: E/AndroidRuntime(862): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080) 
12-17 19:24:04.886: E/AndroidRuntime(862): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573) 
12-17 19:24:04.886: E/AndroidRuntime(862): at java.lang.Thread.run(Thread.java:856) 
12-17 19:24:04.886: E/AndroidRuntime(862): Caused by: java.lang.NullPointerException 
12-17 19:24:04.886: E/AndroidRuntime(862): at com.sara.facebookappl.MainActivity$PostTask.doInBackground(MainActivity.java:97) 
12-17 19:24:04.886: E/AndroidRuntime(862): at com.sara.facebookappl.MainActivity$PostTask.doInBackground(MainActivity.java:1) 
12-17 19:24:04.886: E/AndroidRuntime(862): at android.os.AsyncTask$2.call(AsyncTask.java:287) 
12-17 19:24:04.886: E/AndroidRuntime(862): at java.util.concurrent.FutureTask.run(FutureTask.java:234) 
12-17 19:24:04.886: E/AndroidRuntime(862): ... 4 more

编辑：我改变了它，我仍然得到这些日志猫错误：

12-17 20:22:22.659: E/AndroidRuntime(794): FATAL EXCEPTION: main 
12-17 20:22:22.659: E/AndroidRuntime(794): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.sara.facebookappl/com.sara.facebookappl.MainActivity}:  java.lang.RuntimeException: Only one Looper may be created per thread 
12-17 20:22:22.659: E/AndroidRuntime(794): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180) 
12-17 20:22:22.659: E/AndroidRuntime(794): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230) 
12-17 20:22:22.659: E/AndroidRuntime(794): at android.app.ActivityThread.access$600(ActivityThread.java:141) 
12-17 20:22:22.659: E/AndroidRuntime(794): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234) 
12-17 20:22:22.659: E/AndroidRuntime(794): at android.os.Handler.dispatchMessage(Handler.java:99) 
12-17 20:22:22.659: E/AndroidRuntime(794): at android.os.Looper.loop(Looper.java:137) 
12-17 20:22:22.659: E/AndroidRuntime(794): at android.app.ActivityThread.main(ActivityThread.java:5039) 
12-17 20:22:22.659: E/AndroidRuntime(794): at java.lang.reflect.Method.invokeNative(Native Method) 
12-17 20:22:22.659: E/AndroidRuntime(794): at java.lang.reflect.Method.invoke(Method.java:511) 
12-17 20:22:22.659: E/AndroidRuntime(794): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)

12-1 7 20：22：22.659：E/AndroidRuntime（794）：at com.android.internal.os.ZygoteInit.main（ZygoteInit.java:560） 12-17 20：22：22.659：E/AndroidRuntime（794） dalvik.system.NativeStart.main（本地方法） 12-17 20：22：22.659：E/AndroidRuntime（794）：引起：java.lang.RuntimeException：每个线程只能创建一个Looper 12-17 20：22：22.659：E/AndroidRuntime（794）：在android.os.Looper.prepare（Looper.java:78） 12-17 20：22：22.659：E/AndroidRuntime（794）：at android.os。 Looper.prepare（Looper.java:73） 12-17 20：22：22.659：E/AndroidRuntime（794）：at com.sara.facebookappl.MainActivity.onCreate（MainActivity.java:53） 12-17 20： 22：22.659：E/AndroidRuntime（794）：at android.app.Activity.performCreate（Activity.java:5104） 12-17 20：22：22.659：E/AndroidRuntime（794）：at android.app.Ins trumentation.callActivityOnCreate（Instrumentation.java:1080） 12-17 20：22：22.659：E/AndroidRuntime（794）：在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2144）

来源

2012-12-17 Techno_Wizard

引起：java.lang.NullPointerException在com.sara.facebookappl.MainActivity $ PostTask.doInBackground（MainActivity.java:97） – SLaks

welcome.setText("Welcome, " + name);

除非我错过了某处，我不相信你会正确初始化“欢迎”。我认为你应该在你的onCreate中找到ViewById（）。我怀疑这是nullref。

来源

2012-12-17 20:04:46

Facebook AsyncTask实现

回答

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