Android中的多线程

Question

I'm new to Android and Java. I'm trying to download 1000 plus images. I don't want to do that serially in a UI thread as that will be slow. Hence, I implemented multi-threading using thread and runnable in the below manner.

The for-loop will be called 1000 plus times. So is it an efficient way of achieving it? Will the OS manage the thread pool by its own?

private void syncS3Data() {
    tStart = System.currentTimeMillis();
    try {
        for (final AWSSyncFile f : awsSyncData.getFiles()) {
            new Thread(new Runnable() {

                @Override
                public void run() {
                    beginDownload(f);
                }

            }).start();
        }
    } catch (Exception ex) {
        progressDialog.dismiss();
        showMessage("Error:" + ex.getStackTrace().toString());
    }
}

Answer 1

为确保您无法在MainThread（UI线程）中执行此操作，因为如果执行了此操作，则应用程序将不会响应..然后它将被系统杀死，您可以使用AsyncTask类来执行所需的操作，但我更喜欢使用intentservice，但是您必须使用Intentservice，它是一个工作线程（长时间操作），但是请注意，在完成当前任务之前，intentservice不会执行任何操作，如果您需要并行下载它，则必须使用Service才能正常工作使用UI线程，因此您需要asyncTask才能执行操作，但要确保调用stopSelf（）不同于intentService，一旦完成，它将停止

Answer 2

Instead of creating threads for each download, create one thread and use that for downloading all images.

You can use AsyncTask Refer: https://developer.android.com/reference/android/os/AsyncTask.html

private class DownloadFilesTask extends AsyncTask<SomeObject, Integer, Long> {
    protected Long doInBackground(SomeObject... objs) {

        for (final AWSSyncFile f : obj.getFiles()) {
           beginDownload(f);
        }
    }

    protected void onPostExecute(Long result) {
       //Task Completed
    }

new DownloadFilesTask().execute(someObj);

Answer 3

I had developed an e-commerce app before and have encountered a similar problem in which I had to download some 200+ images for each category.The way I did it was using a loop within an AsyncTask and after each download was completed the image was displayed at the relevant place using the onProgessUpdate() function.I can't share the actual code,so i will give a skeleton example.

public class DownloadImages extends AsyncTask<String,String,String>
{
  File image;
  protected String doInBackground(String... params)
    {
      //download the image here and lets say its stored in the variable file
      //call publishProgress() to run onProgressUpdate()


    }
  protected void onProgressUpdate(String... values)
  {
     //use the image in variable file to update the UI
  }
}