android-只在asynctask完成后完成当前活动

Question

public interface AsyncResponse {
    void processFinish();
} 

// start this activity from MainActivity when the button is pressed
public class login extends AppCompatActivity implements AsyncResponse{
    ...
    BackgroundTask backgroundTask = new BackgroundTask(this);
    backgroundTask.delegate = this;
    backgroundTask.execute("login",user_ac_s,user_pw_s);

    public void processFinish(){
        if(!MainActivity.user_ID.equals("0"))
            finish();
    }
}

public class BackgroundTask extends AsyncTask<String, Void, String>{ 
    ...
    public AsyncResponse delegate = null;
    ...
    protected void onPostExecute(String result) {
        super.onPreExecute();
        if(task.equals("get_userID")){
            MainActivity.user_ID = result;
            delegate.processFinish();
        }
        if(task.equals("register") || task.equals("login")){
            Toast.makeText(context,result,Toast.LENGTH_LONG).show();
            if(result.contains("success")){
                BackgroundTask get_userID_task = new BackgroundTask(context);
                get_userID_task.execute("get_userID",user_ac);
            }
        }
    }
}

错误：------崩溃开始

08-04 05:53:11.807 266 7-2667/com.example.kwei.minigame1 E/AndroidRuntime：致命异常：main process：com.example.kwei.minigame1,PID:2667 java.lang.nullpointerException：试图在com.example.kwei.minigame1.backgroundTask.onPostExecute（backgroundTask.java:26)的com.example.kwei.minigame1.backgroundTask.onPostExecute（.os.asynctask.finish(asynctask.java:636)在Android.os.asynctask.access$500(asynctask.java:177)在Android.os.asynctask$internalhandler.handleMessage(asynctask.java:653)在Android.os.handler.dispatchMessage(handler.java:102)在Android.app.activitythread.main（activitythread.java:5254)在java.lang.reflect.method.invoke（原生方法）在.java:372)at com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:903)at com.Android.internal.os.zygoteinit.main(zygoteinit.java:698)

Answer 1

您的

AsyncResponse委托=null；

委托为空。你还没初始化！

  public AsyncResponse delegate;

  public BackgroundTask(AsyncResponse delegate){
    this.delegate = delagate;
  }

  BackgroundTask backgroundTask = new BackgroundTask(new AsyncResponse()......);
  backgroundTask.delegate = this;// Comment this 
  backgroundTask.execute("login",user_ac_s,user_pw_s);