停止AsyncTask doInBackground方法

Question

我已经在类中创建了一个AsyncTask，并且我正在从一个片段中调用该任务。问题是我想停止doInBackground方法，如果片段被破坏。为此，我在AsyncTask编写的类中创建了一个方法，并在该方法的Asynctask对象上使用了cancel（true）。当我从片段onDestroy（）调用此方法时，后台进程仍在运行。 Plz告诉我停止asynctask的doInBackground的正确方法。

在这里的AsyncTask写入

public class CarDetail implements Parcelable{ 

private String carId; 
private String carName; 
private String imageUrl; 
private String thumbUrl; 
private String dailyPrice; 
private String weeklyPrice; 
private String weekendPrice; 
private String deposit; 
private String minimumAge; 
private String color; 
private String make; 
private String location; 
private String bodyType; 
private String fuelType; 
private String transmission; 
private String carType; 
private String model; 
private String description; 
private Bitmap image; 
private Bitmap thumbImage; 
private CarListAdapter carAdapter; 
private ImageLoadTask task = new ImageLoadTask(); 

public CarDetail() { 
    super(); 
    // TODO Auto-generated constructor stub 
} 

public CarDetail(String carId, String carName, String imageUrl, 
     String thumbUrl, String dailyPrice, String weeklyPrice, 
     String weekendPrice, String deposit, String minimumAge, 
     String color, String make, String location, String bodyType, 
     String fuelType, String transmission, String carType, String model, 
     String description) { 
    super(); 
    this.carId = carId; 
    this.carName = carName; 
    this.imageUrl = imageUrl; 
    this.thumbUrl = thumbUrl; 
    this.dailyPrice = dailyPrice; 
    this.weeklyPrice = weeklyPrice; 
    this.weekendPrice = weekendPrice; 
    this.deposit = deposit; 
    this.minimumAge = minimumAge; 
    this.color = color; 
    this.make = make; 
    this.location = location; 
    this.bodyType = bodyType; 
    this.fuelType = fuelType; 
    this.transmission = transmission; 
    this.carType = carType; 
    this.model = model; 
    this.description = description; 

    // TO BE LOADED LATER - OR CAN SET TO A DEFAULT IMAGE 
    this.image = null; 
    this.thumbImage = null; 
} 

public String getCarId() { 
    return carId; 
} 

public void setCarId(String carId) { 
    this.carId = carId; 
} 

public String getCarName() { 
    return carName; 
} 

public void setCarName(String carName) { 
    this.carName = carName; 
} 

public String getImageUrl() { 
    return imageUrl; 
} 

public void setImageUrl(String imageUrl) { 
    this.imageUrl = imageUrl; 
} 

public String getThumbUrl() { 
    return thumbUrl; 
} 

public void setThumbUrl(String thumbUrl) { 
    this.thumbUrl = thumbUrl; 
} 

public String getDailyPrice() { 
    return dailyPrice; 
} 

public void setDailyPrice(String dailyPrice) { 
    this.dailyPrice = dailyPrice; 
} 

public String getWeeklyPrice() { 
    return weeklyPrice; 
} 

public void setWeeklyPrice(String weeklyPrice) { 
    this.weeklyPrice = weeklyPrice; 
} 

public String getWeekendPrice() { 
    return weekendPrice; 
} 

public void setWeekendPrice(String weekendPrice) { 
    this.weekendPrice = weekendPrice; 
} 

public String getDeposit() { 
    return deposit; 
} 

public void setDeposit(String deposit) { 
    this.deposit = deposit; 
} 

public String getMinimumAge() { 
    return minimumAge; 
} 

public void setMinimumAge(String minimumAge) { 
    this.minimumAge = minimumAge; 
} 

public String getColor() { 
    return color; 
} 

public void setColor(String color) { 
    this.color = color; 
} 

public String getMake() { 
    return make; 
} 

public void setMake(String make) { 
    this.make = make; 
} 

public String getLocation() { 
    return location; 
} 

public void setLocation(String location) { 
    this.location = location; 
} 

public String getBodyType() { 
    return bodyType; 
} 

public void setBodyType(String bodyType) { 
    this.bodyType = bodyType; 
} 

public String getFuelType() { 
    return fuelType; 
} 

public void setFuelType(String fuelType) { 
    this.fuelType = fuelType; 
} 

public String getTransmission() { 
    return transmission; 
} 

public void setTransmission(String transmission) { 
    this.transmission = transmission; 
} 

public String getCarType() { 
    return carType; 
} 

public void setCarType(String carType) { 
    this.carType = carType; 
} 

public String getModel() { 
    return model; 
} 

public void setModel(String model) { 
    this.model = model; 
} 

public String getDescription() { 
    return description; 
} 

public void setDescription(String description) { 
    this.description = description; 
} 

public Bitmap getImage() { 
    return image; 
} 

public void setImage(Bitmap image) { 
    this.image = image; 
} 

public Bitmap getThumbImage() { 
    return thumbImage; 
} 

public void setThumbImage(Bitmap thumbImage) { 
    this.thumbImage = thumbImage; 
} 

public void loadImage(CarListAdapter carAdapter) { 
     // HOLD A REFERENCE TO THE ADAPTER 
     this.carAdapter = carAdapter; 
     if (thumbUrl != null && !thumbUrl.equals("")) { 
      //new ImageLoadTask().execute(thumbUrl); 

      task.execute(thumbUrl); 
     } 
} 

    // ASYNC TASK TO AVOID CHOKING UP UI THREAD 
    private class ImageLoadTask extends AsyncTask<String, String, Bitmap> { 

     @Override 
     protected void onPreExecute() { 
      Log.i("ImageLoadTask", "Loading image..."); 
     } 

     // PARAM[0] IS IMG URL 
     protected Bitmap doInBackground(String... param) { 
      Log.i("ImageLoadTask", "Attempting to load image URL: " + param[0]); 
      try { 
       Bitmap b = JsonParser.downloadBitmap(param[0]); 
       return b; 
      } catch (Exception e) { 
       e.printStackTrace(); 
       return null; 
      } 
     } 

     protected void onProgressUpdate(String... progress) { 
      // NO OP 
     } 

     protected void onPostExecute(Bitmap ret) { 
      if (ret != null) { 
       Log.i("ImageLoadTask", "Successfully loaded " + carName + " image"); 
       image = ret; 
       if (carAdapter != null) { 
        // WHEN IMAGE IS LOADED NOTIFY THE ADAPTER 
        carAdapter.notifyDataSetChanged(); 
       } 
      } else { 
       Log.e("ImageLoadTask", "Failed to load " + carName + " image"); 
      } 
     } 
    } 


    /* everything below here is for implementing Parcelable */ 

    // 99.9% of the time you can just ignore this 
    public int describeContents() { 
     return 0; 
    } 

    // write your object's data to the passed-in Parcel 
    public void writeToParcel(Parcel out, int flags) { 
     out.writeString(carId); 
     out.writeString(carName); 
     out.writeString(imageUrl); 
     out.writeString(thumbUrl); 
     out.writeString(dailyPrice); 
     out.writeString(weeklyPrice); 
     out.writeString(weekendPrice); 
     out.writeString(deposit); 
     out.writeString(minimumAge); 
     out.writeString(color); 
     out.writeString(make); 
     out.writeString(location); 
     out.writeString(bodyType); 
     out.writeString(fuelType); 
     out.writeString(transmission); 
     out.writeString(carType); 
     out.writeString(model); 
     out.writeString(description); 

    } 

    // this is used to regenerate your object. All Parcelables must have a CREATOR that implements these two methods 
    public static final Parcelable.Creator<CarDetail> CREATOR = new Parcelable.Creator<CarDetail>() { 
     public CarDetail createFromParcel(Parcel in) { 
      return new CarDetail(in); 
     } 

     public CarDetail[] newArray(int size) { 
      return new CarDetail[size]; 
     } 
    }; 

    // example constructor that takes a Parcel and gives you an object populated with it's values 
    private CarDetail(Parcel in) { 
     carId = in.readString(); 
     carName = in.readString(); 
     imageUrl = in.readString(); 
     thumbUrl = in.readString(); 
     dailyPrice = in.readString(); 
     weeklyPrice = in.readString(); 
     weekendPrice = in.readString(); 
     deposit = in.readString(); 
     minimumAge = in.readString(); 
     color = in.readString(); 
     make = in.readString(); 
     location = in.readString(); 
     bodyType = in.readString(); 
     fuelType = in.readString(); 
     transmission = in.readString(); 
     carType = in.readString(); 
     model = in.readString(); 
     description = in.readString(); 

    } 



public void stopImageLoadTask(){ 
    task.cancel(true); 
    Log.d("stop", "stop"); 
} 

这是片段的类

public class ServiceCarListFragment extends Fragment { 

private String url; 
private ArrayList<CarDetail> carDetailList = new ArrayList<CarDetail>(); 
private CarListAdapter adapter; 
private ListView mList ; 
private ProgressDialog progressDialog; 
OnCarListItemSelectedListener mCallback; 
private boolean connectionStatus; 

// Container Activity must implement this interface 
public interface OnCarListItemSelectedListener { 
    public void onCarSelected(CarDetail car); 
} 

@Override 
public void onAttach(Activity activity) { 
    // TODO Auto-generated method stub 
    super.onAttach(activity); 
    // This makes sure that the container activity has implemented 
    // the callback interface. If not, it throws an exception 
    try { 
     mCallback = (OnCarListItemSelectedListener) activity; 
    } catch (ClassCastException e) { 
     throw new ClassCastException(activity.toString() 
       + " must implement OnCarListItemSelectedListener"); 
    } 
} 





@Override 
public void onCreate(Bundle savedInstanceState) { 
    // TODO Auto-generated method stub 
    super.onCreate(savedInstanceState); 
    Log.d("Services", "On Create"); 
    url = getActivity().getIntent().getStringExtra("url"); 
    adapter = new CarListAdapter(getActivity() , carDetailList); 

    ConnectionHandler conn = new ConnectionHandler(); 
    connectionStatus = conn.connectionStatus(getActivity()); 

    if(connectionStatus){ 

     new DownloadCarDetail().execute(url); 
    } 

    else{ 
     DialogFragment newFragment = new DialogHandler(getActivity()); 
     newFragment.show(getFragmentManager(), "internet"); 
    } 


} 

@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
     Bundle savedInstanceState) { 
    // TODO Auto-generated method stub 
    Log.d("Services", "On CreateView"); 
    View v = inflater.inflate(R.layout.fragment_service_car_list, container,false); 
    mList = (ListView)v.findViewById(R.id.list); 
    mList.setAdapter(adapter); 
    mList.setOnItemClickListener(new OnItemClickListener() { 

     @Override 
     public void onItemClick(AdapterView<?> parent, View selectedView, int position, 
       long id) { 
      // TODO Auto-generated method stub 
      CarDetail car = (CarDetail)adapter.getItem(position); 
      mCallback.onCarSelected(car); 
     } 
    }); 
    return v; 
} 

class DownloadCarDetail extends AsyncTask<String, String, ArrayList<CarDetail>>{ 



    @Override 
    protected void onPreExecute() { 
     // TODO Auto-generated method stub 
     super.onPreExecute(); 
     progressDialog = ProgressDialog.show(getActivity(), null, "Loading...",true); 

    } 

    @Override 
    protected ArrayList<CarDetail> doInBackground(String... params) { 
     // TODO Auto-generated method stub 
     ArrayList<CarDetail> carDetailList = JsonParser.parseJson(params[0]); 
     return carDetailList; 
    } 

    @Override 
    protected void onPostExecute(ArrayList<CarDetail> carDetailList) { 
     // TODO Auto-generated method stub 
     //adapter = new CarListAdapter(getActivity(),ServiceCarListFragment.this.carDetailList); 
     //mList.setAdapter(adapter); 
     progressDialog.dismiss(); 
     ServiceCarListFragment.this.carDetailList.addAll(carDetailList); 
     adapter.notifyDataSetChanged(); 
     for (CarDetail car : carDetailList) { 
      // START LOADING IMAGES FOR EACH CAR 
      car.loadImage(adapter); 

    } 
     carDetailList.clear(); 
     Log.d("ewgf", String.valueOf(carDetailList.size())); 
} 

} 



@Override 
public void onDestroy() { 
    // TODO Auto-generated method stub 
    super.onDestroy(); 
    new CarDetail().stopImageLoadTask(); 
} 

} 

Answer 1

公共最后布尔取消（布尔mayInterruptIfRunning）

试图取消对此任务的执行。 如果任务已完成，已被取消或由于某些其他原因无法取消，此尝试将失败。如果成功，并且此任务在调用取消时尚未开始，则此任务不应运行。如果任务已经开始，则mayInterruptIfRunning参数确定执行此任务的线程是否应该中断以试图停止任务。

使用isCancelled（）

公共最后布尔isCancelled（）

返回true之前正常完成这个任务被取消。 如果对任务调用cancel（boolean），则应该从doInBackground（Object []）中定期检查此方法返回的值，以尽快结束任务。

Android - Cancel AsyncTask Forcefully

检查接受的答案，并通过commonsware在上面的链接的答案