关于android：一次从AsyncTask下载一项

Download one item at a time from AsyncTask

我有一个片段，其中GridView和ImageViews作为项目。单元格的数量大约为25。

对于每个图像，我都有ID的服务器请求。因此，它有25个服务器请求。耗时2-3秒。

如何一次接收一张图像并将其动态设置为单元格内容？每个没有图像的单元格都应包含ProgressBar。

我现在拥有什么：我正在尝试在AsyncTask中加载项目并将Bitmap数组返回到UI线程。但是我不知道如何为每个图像执行此操作。我的GridView仅在下载了所有图像之后出现。并且应该首先显示25个元素，这些元素包含ProgressBars并且没有图像。

代码代码

片段的onCreate()：

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@Override
public void onCreate(Bundle savedInstanceState) {
...

mItems = new Bitmap[dataChannelsList.size()];

try {
//starting AsyncTask
mItems = new LoadImageAsyncTask(dataChannelsList).execute().get();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
}

LoadImageAsyncTask：

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private class LoadImageAsyncTask extends AsyncTask<Bitmap[], Void, Bitmap[]> {
private ArrayList<DataChannels> dataChannelsList;
private Bitmap[] bitmapList;

public LoadImageAsyncTask(ArrayList<DataChannels> dataChannelsList) {
this.dataChannelsList = dataChannelsList;

bitmapList = new Bitmap[dataChannelsList.size()];
}

protected void onPreExecute() {
super.onPreExecute();
}

protected Bitmap[] doInBackground(Bitmap[]... params) {
for (int i = 0; i < dataChannelsList.size(); i++) {
bitmapList[i] = getChannelImg(dataChannelsList.get(i).getId());
}
return bitmapList;
}

protected void onPostExecute(Bitmap[] param) {
super.onPostExecute(param);
}

private Bitmap getChannelImg(String id) {
...returns Bitmap image by id
}

}

GridView适配器：

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public class GridViewAdapter extends BaseAdapter {
private Context mContext;
private Bitmap[] mItems;

public GridViewAdapter(Context context, Bitmap[] items) {
mContext = context;
mItems = items;
}

@Override
public int getCount() {
return mItems.length;
}

@Override
public Object getItem(int position) {
return mItems[position];
}

@Override
public long getItemId(int position) {
return position;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder viewHolder;

if (convertView == null) {
// inflate the GridView item layout
LayoutInflater inflater = LayoutInflater.from(mContext);
convertView = inflater.inflate(R.layout.gridview_item, parent, false);

// initialize the view holder
viewHolder = new ViewHolder();
viewHolder.ivIcon = (ImageView) convertView.findViewById(R.id.imageview_channelIcon);
viewHolder.progressBar = (ProgressBar) convertView.findViewById(R.id.progress_bar_load_image);
convertView.setTag(viewHolder);
} else {
// recycle the already inflated view
viewHolder = (ViewHolder) convertView.getTag();
}

// update the item view
Bitmap item = mItems[position];

//hide progress bar and bring image to top
viewHolder.progressBar.setVisibility(View.GONE);
viewHolder.ivIcon.setImageBitmap(item);
return convertView;
}

}

private static class ViewHolder {
ImageView ivIcon;
ProgressBar progressBar;
}

伙计们，我真的需要您的帮助。告诉是否需要更多代码或解释。

相关讨论

您可以为此使用publishProgress()来调用onProgressUpdate()

所以在您的for loop中，类似

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for (int i = 0; i < dataChannelsList.size(); i++) {
// create a variable for the current bitmap
Bitmap curBitmap = getChannelImg(dataChannelsList.get(i).getId());
// add it to your list
bitmapList[i] = curBitmap;
// and pass it along
publishProgress(curBitmap);
}

然后您将需要覆盖onProgressUpdate()，由publishProgress()

调用

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@Override
public void onProgressUpdate(Bitmap...progress) {
/* add the bitmap to your list you're using for your adapter here
* and call notifyDataSetChanged() on your adapter
*/
}

然后，您需要将asynctask更改为

1	private class LoadImageAsyncTask extends AsyncTask<Bitmap[], Bitmap, Bitmap[]> {

您也不想在AsyncTask上呼叫.get()，因为它是阻塞呼叫

与此类似的东西应该可以为您提供所需的东西。

替代品

但是，有许多库可以为您完成工作并为您带来收益。

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@Override
public void onCreate(Bundle savedInstanceState) {
...

mItems = new Bitmap[dataChannelsList.size()];
GridView grid=// declare your gridview;
GridViewAdapter adapter=new GridViewAdapter(activityname.this,mItems);
grid.setAdapter(adapter);

try {
//starting AsyncTask here

} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
}

和assynctask

中

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protected void onPostExecute(Bitmap[] param) {
super.onPostExecute(param);
adapter.notifydatasetchanged;

// adapter should be declared as class variable,so that it can be used here.or else pass adapter variable as actual parameter to assynctask constructor

}

对于进度条，我认为您正在做的事是正确的
更改适配器类的

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@Override
public int getCount() {
return 25;// the size you want
}

在getView方法内部

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@Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder viewHolder;

int currentposition=position;
if (convertView == null) {
// inflate the GridView item layout
LayoutInflater inflater = LayoutInflater.from(mContext);
convertView = inflater.inflate(R.layout.gridview_item, parent, false);

// initialize the view holder
viewHolder = new ViewHolder();
viewHolder.ivIcon = (ImageView) convertView.findViewById(R.id.imageview_channelIcon);
viewHolder.progressBar = (ProgressBar) convertView.findViewById(R.id.progress_bar_load_image);
viewHolder.ivIcon.setTag(currentposition);
convertView.setTag(viewHolder);
} else {
// recycle the already inflated view
viewHolder = (ViewHolder) convertView.getTag();
}

// update the item view
Bitmap item = mItems[position];

//hide progress bar and bring image to top

if(Integer.parseInt(viewHolder.ivIcon.getTag().toString())>mItems.size()){
viewHolder.progressBar.setVisibility(View.VISIBLE);
viewHolder.ivIcon.setVisibility(View.VISIBLE);
}
else{
viewHolder.progressBar.setVisibility(View.INVISIBLE);
viewHolder.ivIcon.setVisibility(View.INVISIBLE);

}
viewHolder.ivIcon.setImageBitmap(item);
return convertView;
}

}