向AsyncTask传递参数

Question

嗨，所以我试图通过AsyncTask从url链接抓取图像，抓取图像本身的功能很好。但我想做的是将src变量传递到一个似乎不适合我的asyncTask中。返回值为空。

下面是代码:

 private AsyncTask<String, Void, Drawable> task2;
 Drawable profile;
 public Drawable getProfile(String src){        
    task2 = new AsyncTask<String, Void, Drawable>() {           
        ProgressDialog dialog2;
        InputStream is;
        Drawable d;
        @Override 
        protected void onPreExecute(){
            dialog2 = new ProgressDialog(Thoughts.this, ProgressDialog.STYLE_SPINNER);
            dialog2.setMessage("Loading Data...");          
            dialog2.setCancelable(false);
            dialog2.setCanceledOnTouchOutside(false);   
            dialog2.show();
        }
        @Override
        protected Drawable doInBackground(String... src) {
                try
                {
                    is = (InputStream) new URL(src[0]).getContent();
                    d = Drawable.createFromStream(is, "src name");
                    return d;
                }catch (Exception e) {
                    e.toString();
                    return null;
                }
        }
        @Override
        protected void onPostExecute(Drawable result2) {
            profile = result2; 
            dialog2.dismiss();
        }
    };
    task2.execute(src);
    return profile;
}

在onCreate();

Drawable p4 = getProfile("http://..../xyz.jpg");
Drawable p5 = getProfile("http://..../xyz.jpg");
ImageView thoughtsProfilePic =(ImageView) findViewById(R.id.ivProfilePicData);
ImageView thoughtsProfilePic1 =(ImageView) findViewById(R.id.ivProfilePicData1);
thoughtsProfilePic.setImageDrawable(p4);
thoughtsProfilePic1.setImageDrawable(p5);

Answer 1

AsyncTask帮助您执行异步作业。在你的代码中，我可以看到你在调用它后立即返回Drawable。但是在那一刻，你的asynctask还没有完成，drawable仍然是空的。

task2.execute(src);
return profile;

如果你想在asynctask中完成作业时设置可绘制的资源，只需将ImageView放入你的方法中。应该是:

  public void getProfile(String src, final ImageView v){           
         @Override
    protected void onPostExecute(Drawable result2) {
        // set drawable for ImageView when complete.
        v.setImageDrawable(result2);
        dialog2.dismiss();
    }
    task2.excute(src);
    //do not need return anything.
  } 

使用它:

 ImageView thoughtsProfilePic =(ImageView) findViewById(R.id.ivProfilePicData);
 getProfile("http://..../xyz.jpg", thoughtsProfilePic );

希望有帮助。

:
没有办法从异步方法直接返回值，这里是另一种选择。首先，创建一个接口，在完成作业时通知。

 public interface INotifyComplete{  
      public void onResult(Drawable result);  
 } 

那么你的activity类应该看起来像:

 public class YourActivity extends Activity implement INotifyComplete{
 private Drawable res1;
 private Drawable res2;
 public void onResult(Drawable result){
    if(result == res1){
        // do something with resource 1
        ImageView thoughtsProfilePic =(ImageView) findViewById(R.id.ivProfilePicData);
        thoughtsProfilePic.setImageDrawable(result);
    }
    if(result == res2){
        // do something with resource 2
    }
  }
 void someMethod(){
// you can use this way to call
    getProfile("http://..../xyz.jpg", res1, YourActivity.this);
    //or this
    getProfile("http://..../xyz.jpg", res2, new INotifyComplete(){
        public void onResult(Drawable result){
            // result is res2, so don't need to check
        }
    });
 }
 public void getProfile(String src, final Drawable res, final INotifyComplete notify){
   //don't need store asynctask instance
    AsyncTask<String, Void, Drawable>  task2 = new AsyncTask<String, Void, Drawable>(){
        // do something ...
        protected void onPostExecute(Drawable result2) {             
        dialog2.dismiss();
        // you will set the value to your drawable then notify it when complete job
        res = result2;
        notify.onResult(res);
    }
    }
    task2.excute();
}
  }

Answer 2

在你的活动中写一个公共成员函数，它返回drawable，只是在你的asyncTask类的doInBackground()方法中调用函数。

Drawable downloadImage(){
//write code here to download image so you can return any dataType
}

现在只需在doInBackground()方法中调用这个函数，并将返回的结果保存在activity的某个变量中。

void doInBackground(){
    drawableVariable = downloadImage();    
}

编辑:asyncTask是你的后台线程，而不是UI线程，所以如果你想做任何UI工作，那么你必须通过runOnUiThread()方法在UI线程中执行该工作

runOnUiThread(new Runnable() {
           @Override
           public void run() {
               /* update your UI here for example what you are doing something */;
               profile = result2;
           }
       });