我想使用android downloadManager从URL下载文件,并使用进度条显示下载进度。
xml文件:
<ProgressBar
android:id="@+id/progress_bar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="10dp"
android:layout_alignParentBottom="true"
android:progressTint="@color/downloadColorDark"
style="@android:style/Widget.Holo.Light.ProgressBar.Horizontal"/>
下载片段代码:
Button buttonDownload;
DownloadManager downloadManager;
protected ProgressBar mProgressBar;
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_download, container, false);
buttonDownload = (Button)view.findViewById(R.id.downloadMusicButton);
buttonDownload.setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View view){
downloadManager = (DownloadManager)getActivity().getSystemService(Context.DOWNLOAD_SERVICE);
Uri uri = Uri.parse("http://org3.s1.mp3.zdn.vn/871a49ac2fe8c6b69ff9/6036763354470939079?key=r-YWGIWypTz_FZeaVGri_Q&expires=1480915451&filename=Iridescent%20Linkin%20Park%20Linkin%20Park%20-%20Linkin%20Park.mp3");
DownloadManager.Request request = new DownloadManager.Request(uri);
request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
final long downloadId = downloadManager.enqueue(request);
mProgressBar = (ProgressBar)view.findViewById(R.id.progress_bar);
Timer myTimer = new Timer();
myTimer.schedule(new TimerTask() {
@Override
public void run() {
DownloadManager.Query q = new DownloadManager.Query();
q.setFilterById(downloadId);
Cursor cursor = downloadManager.query(q);
cursor.moveToFirst();
int bytes_downloaded = cursor.getInt(cursor.getColumnIndex(DownloadManager.COLUMN_BYTES_DOWNLOADED_SO_FAR));
int bytes_total = cursor.getInt(cursor.getColumnIndex(DownloadManager.COLUMN_TOTAL_SIZE_BYTES));
cursor.close();
final int dl_progress = (bytes_downloaded * 100 / bytes_total);
getActivity().runOnUiThread(new Runnable(){
@Override
public void run(){
mProgressBar.setProgress(dl_progress);
}
});
}
}, 0, 10);
}
});
return view;
}
下载功能完美无缺,但在我添加了进度条的代码后,当我按下载按钮时,应用程序崩溃了。请告诉我我做错了什么。
错误消息:
E/AndroidRuntime: FATAL EXCEPTION: main
Process: vn.edu.usth.musicplayer, PID: 4456
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ProgressBar.setProgress(int)' on a null object reference
at vn.edu.usth.musicplayer.fragment.DownloadFragment$1$1$1.run(DownloadFragment.java:73)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
答案 0 :(得分:2)
如果您使用ProgressDialog
实施AsyncTask
,则很容易。
使用以下代码实现进度条。
private class DownloadTask extends AsyncTask<String, Integer, Void> {
ProgressDialog dialog = new ProgressDialog(MainActivity.this);
@Override
protected void onPreExecute() {
//set message of the dialog
dialog.setMessage("Loading...");
//show dialog
dialog.show();
super.onPreExecute();
}
protected Void doInBackground(String... args) {
// do background work here
return null;
}
@Override
protected void onProgressUpdate(Integer... values) {
// Update download Progress
super.onProgressUpdate(values);
}
protected void onPostExecute(List<Transaction> result) {
// do UI work here
if(dialog != null && dialog.isShowing()){
dialog.dismiss()
}
}
}