在测试异步任务完成之前，ImageDownload异步任务即将启动。

Question

public class DetailsActivity extends Activity {

private ArrayAdapter<Imageclass> adapter;
ArrayList<String> imageselect = new ArrayList<String>();
private ArrayList<Imageclass> array1;
private ArrayList<Imageclass> list = new ArrayList<Imageclass>();
//private ArrayList<Imageclass> array;
ArrayList<String> imagetest = new ArrayList<String>();
private TextView textView1; 
private TextView textView2;
private TextView textView3;
private TextView textView4;
private TextView textView5;
int id;
int pid;
int val;
int val_new;
double lati;
double longi;
String imagename;
//private ImageView image;
//public static final String URL = "http://theopentutorials.com/totwp331/wp-content/uploads/totlogo.png";
ImageView image;
static Bitmap bm;
ProgressDialog pd;


BitmapFactory.Options bmOptions;

public class test extends AsyncTask<Void, Void, InputStream>{

    ArrayList<Imageclass> str;

    private DetailsActivity activity;


    public test(DetailsActivity activity){
        this.activity = activity;
    }


    @Override
    protected InputStream doInBackground(Void... params) {

        //String stringURL = "http://192.168.2.104:8088/Image/MyImage" + String.format("?id=%d",id); 
        Log.e("Checking id",""+id);

        String stringURL = "http://megavenues.org/mobile_json/get_images" + String.format("?id=%d",id);
        URL url; 
        try {
            stringURL=stringURL.replaceAll(" ", "%20");

            url = new URL(stringURL);
            Log.e("URL",""+ url); 

            URLConnection conn= url.openConnection();

            Log.e("URLConnection",""+conn );
            InputStream stream= conn.getInputStream(); 

            Log.e("URLStream",""+stream );

            return stream; 
        } catch (MalformedURLException e) { 

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

            Log.e("Excepiton", ""+e);
            e.printStackTrace();
        }
        return null;
    }       

    @Override
    protected void onPostExecute(InputStream result) {
        super.onPostExecute(result);
        Log.e("Result", ""+result);
        StringBuilder builder = new StringBuilder();
        Log.e("Builder", ""+ builder);
        BufferedReader reader = new BufferedReader(new InputStreamReader(result));
        Log.e("Reader", ""+ reader);

        String line = null;
        try {
            while((line = reader.readLine()) != null) {
                Log.e("Result11", ""+ builder.append(line));
                builder.append(line);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }


        String jsonString = builder.toString();
        Log.e("image", jsonString);

        try {

            JSONObject rootObject = new JSONObject(jsonString);
            Log.e("JSOnObject",""+ rootObject);
            JSONArray jsonArray = rootObject.getJSONArray("tbl_ads_images");        
            //array1.clear();
            ArrayList<String> imagearray = new ArrayList<String>();
            for (int index = 0; index < jsonArray.length(); index++) {
                Imageclass imageinstance = new Imageclass(); 

                JSONObject object = (JSONObject) jsonArray.get(index);
                Log.e("Image test", "" + object);
                imageinstance.image = object.getString("file_name");

                //### this contain the image name
                Log.e("Imageinstance.image",""+imageinstance.image);

                imagename = imageinstance.image;
                imagearray.add(imageinstance.image);


                array1.add(imageinstance);
                //array1.add(imagearray);
                Log.e("array1","test"+array1);
            }
            Log.e("IMAGES",""+array1);
            activity.setlist(array1);


        }       
        catch (JSONException e) {
            Log.e("this Exception",""+ e);
            e.printStackTrace();
        }
        catch (Exception e) {
            Log.e("NULL","NULL"+e);
        }

        //  adapter.notifyDataSetChanged();


    }

}

public class ImageDownload extends AsyncTask<String, Void, String> {

    protected String doInBackground(String... param) {
        bmOptions = new BitmapFactory.Options();
        bmOptions.inSampleSize = 1;

        String imageUrl ="http://megavenues.com/assets/uploads/users/"+val+"/ads/thumbnail/"+Finalname;
        Log.e("inside img",""+Finalname);
        Log.e("inside img_val",""+val);
        Log.e("Check","check"+imageUrl);
        loadBitmap(imageUrl, bmOptions);
        return imageUrl;
    }

    protected void onPostExecute(String imageUrl) {
        pd.dismiss();
        if (!imageUrl.equals("")) {
            Log.e("Test","Test"+ imageUrl.equals(""));
            image.setImageBitmap(bm);
        } else {
            Toast.makeText(DetailsActivity.this,
                    "test", Toast.LENGTH_LONG)
                    .show();
        }
    }

}

public static Bitmap loadBitmap(String URL, BitmapFactory.Options options) {
    InputStream in = null;
    try {
        in = OpenHttpConnection(URL);
        bm = BitmapFactory.decodeStream(in, null, options);
        in.close();
    } catch (IOException e1) {
    }
    return bm;
}

private static InputStream OpenHttpConnection(String strURL)
        throws IOException {
    InputStream inputStream = null;
    URL url = new URL(strURL);
    URLConnection conn = url.openConnection();

    try {
        HttpURLConnection httpConn = (HttpURLConnection) conn;
        httpConn.setRequestMethod("GET");
        httpConn.connect();

        if (httpConn.getResponseCode() == HttpURLConnection.HTTP_OK) {
            inputStream = httpConn.getInputStream();
        }
    } catch (Exception ex) {
    }
    return inputStream;
}

String Finalname;

//String imageUrl ="http://megavenues.com/assets/uploads/users/220/ads/thumbnail/"+Finalname;
public void setlist(ArrayList<Imageclass> list)
{
    this.list= list; 
    Log.e("LIST",""+ this.list);
    String imagename1 = list.toString();
    Log.e("image new value",""+imagename1);
    this.list= list; 
    Log.e("testing",""+ this.list); 
    for (int i=0; i < list.size(); i++)
    { 
        Log.e("new check",""+list.get(i));
        //String test2= list.get(i).toString();
        imagetest.add(list.get(i).toString());  
        Finalname = list.get(i).toString();
        getimage_name(Finalname);
        Log.e("Come",""+list.get(i).toString());
        Log.e("Finalname",""+Finalname);
    }
}
//String imageUrl ="http://megavenues.com/assets/uploads/users/"+val+"/ads/thumbnail/"+Finalname;

private void getimage_name(String finalname2) {


}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_details);
    image = (ImageView)findViewById(R.id.imageView2);


    //  getMenuInflater().inflate(R.menu.details);
    //R.id.textDetailPlace 
    textView1 = (TextView)findViewById(R.id.textDetailPlace);
    textView2 = (TextView)findViewById(R.id.textDetailAddress ); 
    textView3 = (TextView)findViewById(R.id.textCapacity);
    //  textView4 = (TextView)findViewById(R.id.textDetailContactNo);
    textView5 = (TextView) findViewById(R.id.textViewDescription);


    textView1.setText(getIntent().getExtras().getString("test"));
    textView2.setText(getIntent().getExtras().getString("test2"));
    textView3.setText(getIntent().getExtras().getString("test3"));
    //textView4.setText(getIntent().getExtras().getString("test4"));
    textView5.setText(getIntent().getExtras().getString("test5"));

    id = getIntent().getExtras().getInt("test6");
    Log.e("ID value",""+id);

    pid = getIntent().getExtras().getInt("test7");
    Log.e("PID value",""+pid);

    lati = getIntent().getExtras().getDouble("testlat");
    Log.e("long",""+lati);
    longi = getIntent().getExtras().getDouble("testlong");
    Log.e("long",""+longi);
    val=pid;
    Log.e("val",""+val);
    ActionBar actionBar = getActionBar();
    actionBar.hide();
    pd = ProgressDialog.show(DetailsActivity.this, null, null,true);
    pd.setContentView(R.layout.progress);
    array1 = new ArrayList<Imageclass>();
    //new test(this).execute();

    new test(this).execute();

这里，测试异步任务被调用

    Log.e("JUST","CHECK");
    Log.e("JUST","CHECK");


    try {
        Thread.sleep(1000);
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

这里调用的是imageDownload异步任务：

    new ImageDownload().execute();

        Log.e("imagename",""+imagename);
}
}

在测试异步任务完成之前，在ImageDownload开始执行之前

我无法得到任务的状态，你能知道它是如何完成的吗？

Answer 1

随着时间的推移，安卓处理AsyncTasks的方式也发生了一些变化。在非常老的安卓版本(前1.6AFAIK)中，多个AsyncTasks按顺序执行。这种行为已经改变为并行运行AsyncTasks，直到Android2.3。从Android3.0开始，Android团队决定人们在同步并行运行的任务时不够小心，并将默认行为切换回顺序执行。在内部，AsyncTask使用可以配置为按顺序(默认)或按需要并行运行的ExecutionService：

ImageLoader imageLoader = new ImageLoader( imageView );
imageLoader.executeOnExecutor( AsyncTask.THREAD_POOL_EXECUTOR, "http://url.com/image.png"    );

Answer 2

无论我从这里了解到什么，您都希望在任务线程之后执行ImageDownload线程，因此从任务线程的onPostExecute()启动ImageDownload线程

Answer 3

在执行异步任务时，将启动一个新线程，但当前线程将继续运行。它在启动thread.sleep后立即运行到test.async (1000)中。

它看起来像是在test.async中下载一些互联网，正如您可能已经猜到的，它需要超过1000毫秒(1秒)。这意味着1秒后，您的另一个异步将在第一个完成之前启动。

我猜你是想把他们弄乱。在第一个异步的postExecute中，您可以生成第二个异步。更正确的方法是在您的活动上实现一个接口，该接口在异步完成时进行回调，然后在收到回调后启动第二个异步。

下面是一个如何构造这个结构的例子。

interface AsyncCallback{
void onAsyncComplete();
}

public class ExampleActivity extends Activity implements AsyncCallback {

....

public void launchFirstAsync(){
    new Task(this).execute();
}


@Override
public void onAsyncComplete() {
    //todo launch second asyncTask;

   }
}

class Task extends AsyncTask<Void, Void, Void>{

AsyncCallback cb;

Task(AsyncCallback cb){
    this.cb = cb;
}

@Override
protected Void doInBackground(Void... params) {
    // TODO Auto-generated method stub
    return null;
}

@Override
protected void onPreExecute() {
    // TODO Auto-generated method stub
    super.onPreExecute();

    cb.onAsyncComplete();
}

}