android - 在 doInBackground 中运行的异步任务 2 函数

Question

你好，我想使用异步任务，这是我的骨架代码:

public class MyActivity extends Activity {
    private ProgressDialog pd = null;
    private Object data = null;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        // Show the ProgressDialog on this thread
        this.pd = ProgressDialog.show(this, "Working..", "Downloading Data...", true, false);

        // Start a new thread that will download all the data
        new DownloadTask().execute("Any parameters my download task needs here");
    }

    private class DownloadTask extends AsyncTask<String, Void, Object> {
         protected Object doInBackground(String... args) {
             Log.i("MyApp", "Background thread starting");

             // This is where you would do all the work of downloading your data

             return "replace this with your data object";
         }

         protected void onPostExecute(Object result) {
             // Pass the result data back to the main activity
             MyActivity.this.data = result;

             if (MyActivity.this.pd != null) {
                 MyActivity.this.pd.dismiss();
             }
         }
    }  

我的问题是，如果我的 InBackground 函数同时返回字符串数组和位图，那么 AsyncTask 中的第三个参数应该是什么？有什么帮助吗？

Answer 1

您可以使用 Bundle(参见 http://developer.android.com/reference/android/os/Bundle.html)。所以你的 AsyncTask 看起来像......

public class MyTask extends AsyncTask<Void, Void, Bundle> 
{
  @Override
  protected Bundle doInBackground(Void... arg) 
  {
    Bundle bundle = new Bundle();
    bundle.putParcelable("Bitmap", bitmap);
    bundle.putString("String", string);

    return bundle;
  }
  protected void onPostExecute(Bundle bundle) 
  {
    Bitmap bitmap = bundle.getParcelable("Bitmap");
    String string = bundle.getString("String");
  }
}

位图是可打包的，但除了最小的位图，您很可能会遇到运行时错误。所以你可能需要把它变成一个字节数组然后再变回去，就像这样……

ByteArrayOutputStream baos = new ByteArrayOutputStream();
bitmap.compress(Bitmap.CompressFormat.PNG, 100, baos);
byte[] bytes = baos.toByteArray();
Bundle bundle = new Bundle();
bundle.putByteArray("Bytes", bytes);

还有这个……

byte[] bytes = bundle.getByteArray("Bytes");
Bitmap bitmap = BitmapFactory.decodeByteArray(bytes, 0, bytes.length, new BitmapFactory.Options());