我正在尝试ListView使用下载任务列表创建一个。
下载任务在Service(DownloadService) 中进行管理。每次接收到一大块数据时，任务通过 a 发送进度Broadcast，由Fragment包含ListView(SavedShowListFragment) 接收。收到Broadcast消息后，SavedShowListFragment 会更新适配器中下载任务的进度并触发notifyDataSetChanged().
列表中的每一行都包含一个ProgressBar，aTextView代表正在下载的文件的标题，一个代表进度的数值，aButton用于在下载完成时暂停/恢复下载或播放保存的节目。
问题是暂停/恢复/播放Button通常没有响应（onClick()没有被调用），我认为这是因为整个列表的更新非常频繁notifyDataSetChanged()（每次接收到一大块数据，即 1024 字节，这可以是每秒多次，尤其是当有多个下载任务正在运行时）。
我想我可以在下载任务中增加数据块的大小，但我真的认为我的方法根本不是最优的！
频繁调用会notifyDataSetChanged()导致ListViewUI 无响应吗？
有没有办法只更新行Views中的一些ListView，即在我的情况下ProgressBar和TextView与进度的数值，而不调用notifyDataSetChanged()，更新整个列表？
更新下载任务的进度ListView，有没有比“getChunk/sendBroadcast/updateData/notifyDataSetChanged”更好的选择？
以下是我的代码的相关部分。
下载服务中的下载任务
public class DownloadService extends Service {
//...
private class DownloadTask extends AsyncTask<SavedShow, Void, Map<String, Object>> {
//...
@Override
protected Map<String, Object> doInBackground(SavedShow... params) {
//...
BufferedInputStream in = new BufferedInputStream(connection.getInputStream());
byte[] data = new byte[1024];
int x = 0;
while ((x = in.read(data, 0, 1024)) >= 0) {
if(!this.isCancelled()){
outputStream.write(data, 0, x);
downloaded += x;
MyApplication.dbHelper.updateSavedShowProgress(savedShow.getId(), downloaded);
Intent intent_progress = new Intent(ACTION_UPDATE_PROGRESS);
intent_progress.putExtra(KEY_SAVEDSHOW_ID, savedShow.getId());
intent_progress.putExtra(KEY_PROGRESS, downloaded );
LocalBroadcastManager.getInstance(DownloadService.this).sendBroadcast(intent_progress);
}
else{
break;
}
}
//...
}
//...
}
}
SavedShowListFragment
public class SavedShowListFragment extends Fragment {
//...
@Override
public void onResume() {
super.onResume();
mAdapter = new SavedShowAdapter(getActivity(), MyApplication.dbHelper.getSavedShowList());
mListView.setAdapter(mAdapter);
//...
}
private ServiceConnection mDownloadServiceConnection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName className, IBinder service) {
// Get service instance
DownloadServiceBinder binder = (DownloadServiceBinder) service;
mDownloadService = binder.getService();
// Set service to adapter, to 'bind' adapter to the service
mAdapter.setDownloadService(mDownloadService);
//...
}
@Override
public void onServiceDisconnected(ComponentName arg0) {
// Remove service from adapter, to 'unbind' adapter to the service
mAdapter.setDownloadService(null);
}
};
private BroadcastReceiver mMessageReceiver = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();
if(action.equals(DownloadService.ACTION_UPDATE_PROGRESS)){
mAdapter.updateItemProgress(intent.getLongExtra(DownloadService.KEY_SAVEDSHOW_ID, -1),
intent.getLongExtra(DownloadService.KEY_PROGRESS, -1));
}
//...
}
};
//...
}
SavedShowAdapter
public class SavedShowAdapter extends ArrayAdapter<SavedShow> {
private LayoutInflater mLayoutInflater;
private List<Long> mSavedShowIdList; // list to find faster the position of the item in updateProgress
private DownloadService mDownloadService;
private Context mContext;
static class ViewHolder {
TextView title;
TextView status;
ProgressBar progressBar;
DownloadStateButton downloadStateBtn;
}
public static enum CancelReason{ PAUSE, DELETE };
public SavedShowAdapter(Context context, List<SavedShow> savedShowList) {
super(context, 0, savedShowList);
mLayoutInflater = (LayoutInflater) context.getSystemService( Context.LAYOUT_INFLATER_SERVICE );
mContext = context;
mSavedShowIdList = new ArrayList<Long>();
for(SavedShow savedShow : savedShowList){
mSavedShowIdList.add(savedShow.getId());
}
}
public void updateItemProgress(long savedShowId, long progress){
getItem(mSavedShowIdList.indexOf(savedShowId)).setProgress(progress);
notifyDataSetChanged();
}
public void updateItemFileSize(long savedShowId, int fileSize){
getItem(mSavedShowIdList.indexOf(savedShowId)).setFileSize(fileSize);
notifyDataSetChanged();
}
public void updateItemState(long savedShowId, int state_ind, String msg){
SavedShow.State state = SavedShow.State.values()[state_ind];
getItem(mSavedShowIdList.indexOf(savedShowId)).setState(state);
if(state==State.ERROR){
getItem(mSavedShowIdList.indexOf(savedShowId)).setError(msg);
}
notifyDataSetChanged();
}
public void deleteItem(long savedShowId){
remove(getItem((mSavedShowIdList.indexOf(savedShowId))));
notifyDataSetChanged();
}
public void setDownloadService(DownloadService downloadService){
mDownloadService = downloadService;
notifyDataSetChanged();
}
@Override
public View getView(final int position, View convertView, ViewGroup parent) {
ViewHolder holder;
View v = convertView;
if (v == null) {
v = mLayoutInflater.inflate(R.layout.saved_show_list_item, parent, false);
holder = new ViewHolder();
holder.title = (TextView)v.findViewById(R.id.title);
holder.status = (TextView)v.findViewById(R.id.status);
holder.progressBar = (ProgressBar)v.findViewById(R.id.progress_bar);
holder.downloadStateBtn = (DownloadStateButton)v.findViewById(R.id.btn_download_state);
v.setTag(holder);
} else {
holder = (ViewHolder) v.getTag();
}
holder.title.setText(getItem(position).getTitle());
Integer fileSize = getItem(position).getFileSize();
Long progress = getItem(position).getProgress();
if(progress != null && fileSize != null){
holder.progressBar.setMax(fileSize);
holder.progressBar.setProgress(progress.intValue());
holder.status.setText(Utils.humanReadableByteCount(progress) + " / " +
Utils.humanReadableByteCount(fileSize));
}
holder.downloadStateBtn.setTag(position);
SavedShow.State state = getItem(position).getState();
/* set the button state */
//...
/* set buton onclicklistener */
holder.downloadStateBtn.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
int position = (Integer) v.getTag();
SavedShow.State state = getItem(position).getState();
if(state==SavedShow.State.DOWNLOADING){
getItem(position).setState(SavedShow.State.WAIT_PAUSE);
notifyDataSetChanged();
mDownloadService.cancelDownLoad(getItem(position).getId(), CancelReason.PAUSE);
}
else if(state==SavedShow.State.PAUSED || state==SavedShow.State.ERROR){
getItem(position).setState(SavedShow.State.WAIT_DOWNLOAD);
notifyDataSetChanged();
mDownloadService.downLoadFile(getItem(position).getId());
}
if(state==SavedShow.State.DOWNLOADED){
/* play file */
}
}
});
return v;
}
}