使用AsyncTask的加载图像到自定义适配器 [英] Using AsyncTask to load images into a custom adapter

问题描述

虽然有很多的教程在那里，我发现这真的是难以实施的AsyncTask加载从URI的（从内容提供商处获得）的图像到一个自定义的适配器。

Although there are many tutorials out there, I've found it really difficult to implement an AsyncTask to load images from URI's (obtained from a content provider) into a custom adapter.

我得到的基本精神，这是有包含的AsyncTask一类，做位图建立在doInBackground，然后设置在onPostExecute ImageView的。

I get the basic gist, which is to have a class containing an AsyncTask, do the bitmap creation in the 'doInBackground', and then set the ImageView in the onPostExecute.

我的问题，是新的到Android和放大器;编程，是我不知道如何在我的URI传递给AsyncTask的每个项目，如何创建位图，以及如何将其恢复到适配器。

The problem for me, being new to android & programming, is that I don't know how to pass in my Uri's to the AsyncTask for each item, how to create the bitmap, and how to return it to the adapter.

我只得到了这一步实际的AsyncTask类（ImageLoader的）：

I've only gotten this far with the actual AsyncTask class (ImageLoader):

package another.music.player;

import android.graphics.Bitmap;
import android.os.AsyncTask;
import android.widget.ImageView;

public class ImageLoader extends AsyncTask<String, String, Bitmap> {

    private ImageView imageView;
    private Bitmap bitmap = null;

    @Override
    protected Bitmap doInBackground(String... uri) {

        // Create bitmap from passed in Uri here

        return bitmap;

    }

    @Override
    protected void onPostExecute(Bitmap bitmap) {
        if (bitmap != null && imageView != null) {
            imageView.setImageBitmap(bitmap);

        }
    }
}

和我的自定义适配器是这样的：

And my custom adapter looks like this:

package another.music.player;

import android.content.ContentUris;
import android.content.Context;
import android.database.Cursor;
import android.net.Uri;
import android.provider.BaseColumns;
import android.provider.MediaStore.Audio.AlbumColumns;
import android.provider.MediaStore.Audio.AudioColumns;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.CursorAdapter;
import android.widget.ImageView;
import android.widget.TextView;

class AlbumAdapter extends CursorAdapter {

    public AlbumAdapter(Context context, Cursor c, int flags) {
        super(context, c, flags);
    }

    private static Uri currentSongUri;

    @Override
    public void bindView(View view, Context context, Cursor cursor) {
        ImageView albumArt = (ImageView) view.getTag(R.id.albumArt);
        TextView text1 = (TextView) view.getTag(R.id.artistTitle);
        TextView text2 = (TextView) view.getTag(R.id.albumTitle);
        TextView text3 = (TextView) view.getTag(R.id.totalSongs);

        albumArt.setImageBitmap(null);

        text1.setText(cursor.getString(cursor
                .getColumnIndex(AudioColumns.ARTIST)));
        text2.setText(cursor.getString(cursor
                .getColumnIndex(AudioColumns.ALBUM)));
        text3.setText(cursor.getString(cursor
                .getColumnIndex(AlbumColumns.NUMBER_OF_SONGS)));

        String currentAlbumId = cursor.getString(cursor
                .getColumnIndex(BaseColumns._ID));

        Integer currentAlbumIdLong = Integer.parseInt(currentAlbumId);
        Uri artworkUri = Uri.parse("content://media/external/audio/albumart");
        currentSongUri = ContentUris.withAppendedId(artworkUri,
                currentAlbumIdLong);

        //Run ImageLoader AsyncTask here, and somehow retrieve the ImageView & set it.

    }

    @Override
    public View newView(Context context, Cursor cursor, ViewGroup parent) {
        LayoutInflater inflater = LayoutInflater.from(context);
        View view = inflater.inflate(R.layout.albumitem, null);
        view.setTag(R.id.albumArt, view.findViewById(R.id.albumArt));
        view.setTag(R.id.artistTitle, view.findViewById(R.id.artistTitle));
        view.setTag(R.id.albumTitle, view.findViewById(R.id.albumTitle));
        view.setTag(R.id.totalSongs, view.findViewById(R.id.totalSongs));

        return view;
    }

}

我会很感激，如果有人能告诉我如何处理这个问题。

I would be very grateful if somebody could show me how to proceed with this.

感谢。

推荐答案

您需要通过您的的AsyncTask 视图，以便它可以在完成时更新：

You need to pass your AsyncTask the view so that it can update it when it completes:

//Run ImageLoader AsyncTask here, and let it set the ImageView when it is done.
new ImageLoader().execute(view, uri);

和修改的AsyncTask ，以便它可以处理混合参数类型：

And modify AsyncTask so that it can handle mixed parameter types:

public class ImageLoader extends AsyncTask<Object, String, Bitmap> {

    private View view;
    private Bitmap bitmap = null;

    @Override
    protected Bitmap doInBackground(Object... parameters) {

        // Get the passed arguments here
        view = (View) parameters[0];
        String uri = (String)parameters[1];

        // Create bitmap from passed in Uri here
        // ...
        return bitmap;
    }

    @Override
    protected void onPostExecute(Bitmap bitmap) {
        if (bitmap != null && view != null) {
            ImageView albumArt = (ImageView) view.getTag(R.id.albumArt);
            albumArt.setImageBitmap(bitmap);
        }
    }
}

我没有测试此code，但它应该给你一个想法。

I haven't tested this code but it should give you an idea.

这篇关于使用AsyncTask的加载图像到自定义适配器的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！