如何使用异步任务进行下载

Question

我正在开发我的第一个项目android下载管理器如何使用异步任务进行Muti线程下载，如ADM app

Answer 1

您将使用此类，并且回调是您的活动（如果需要）

public class TaskDownloader extends Fragment {

    private static final String TAG = TaskDownloader.class.getSimpleName();
    private static final boolean DEBUG = true; // Set this to false to disable logs.


    /**
     * Callback interface through which the fragment can report the task's
     * progress and results back to the Activity.
     */
    public static interface TaskCallbacks {
        void onPreExecute();

        void onProgressUpdate(int percent);

        void onCancelled();

        void onPostExecute(boolean result);
    }


    private TaskCallbacks mCallbacks;
    private DownloadFileTask mTask;
    private boolean mRunning;

    /**
     * Hold a reference to the parent Activity so we can report the task's current
     * progress and results. The Android framework will pass us a reference to the
     * newly created Activity after each configuration change.
     */
    @Override
    public void onAttach(Activity activity) {
        if (DEBUG) Log.i(TAG, "onAttach(Activity)");
        super.onAttach(activity);
        if (!(activity instanceof TaskCallbacks)) {
            throw new IllegalStateException("Activity must implement the TaskCallbacks interface.");
        }

        // Hold a reference to the parent Activity so we can report back the task's
        // current progress and results.
        mCallbacks = (TaskCallbacks) activity;
    }



    /**
     * This method is called once when the Fragment is first created.
     */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        if (DEBUG) Log.i(TAG, "onCreate(Bundle)");
        super.onCreate(savedInstanceState);
        setRetainInstance(true);
    }

    /**
     * Note that this method is <em>not</em> called when the Fragment is being
     * retained across Activity instances. It will, however, be called when its
     * parent Activity is being destroyed for good (such as when the user clicks
     * the back button, etc.).
     */
    @Override
    public void onDestroy() {
        if (DEBUG) Log.i(TAG, "onDestroy()");
        super.onDestroy();
        cancel();
    }

    /*****************************/
    /***** TASK FRAGMENT API *****/
    /*****************************/

    /**
     * Start the background task.
     */
    public void start() {
        if (!mRunning) {
            mTask = new DownloadّFileTask();
            mTask.execute();
            mRunning = true;
        }
    }

    /**
     * Cancel the background task.
     */
    public void cancel() {
        if (mRunning) {
            mTask.cancel(false);
            mTask = null;
            mRunning = false;
        }
    }

    /**
     * Returns the current state of the background task.
     */
    public boolean isRunning() {
        return mRunning;
    }

    /***************************/
    /***** BACKGROUND TASK *****/
    /**
     * ***********************
     */

    private class DownloadFileTask extends AsyncTask<Void, String, Boolean> {

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            if (mCallbacks != null)
                mCallbacks.onPreExecute();


        }

        @Override
        protected Boolean doInBackground(Void... voids) {

         //downloadFile
        }

        @Override
        protected void onProgressUpdate(String... values) {
            super.onProgressUpdate(values);

            if (mCallbacks != null)
                mCallbacks.onProgressUpdate(Integer.parseInt(values[0]));

        }

        @Override
        protected void onPostExecute(Boolean result) {
            super.onPostExecute(result);
            if (mCallbacks != null)
                mCallbacks.onPostExecute(result);
            mRunning = false;


        }

        @Override
        protected void onCancelled() {
            super.onCancelled();
            if (mCallbacks != null)
                mCallbacks.onCancelled();
            mRunning = false;
        }
    }

    /************************/
    /***** LOGS & STUFF *****/
    /**
     * ********************
     */

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        if (DEBUG) Log.i(TAG, "onActivityCreated(Bundle)");
        super.onActivityCreated(savedInstanceState);
    }

    @Override
    public void onStart() {
        if (DEBUG) Log.i(TAG, "onStart()");
        super.onStart();
    }

    @Override
    public void onResume() {
        if (DEBUG) Log.i(TAG, "onResume()");
        super.onResume();
    }

    @Override
    public void onPause() {
        if (DEBUG) Log.i(TAG, "onPause()");
        super.onPause();
    }

    @Override
    public void onStop() {
        if (DEBUG) Log.i(TAG, "onStop()");
        super.onStop();
    }

}