Question

如果您查看此问题Update adapter from different method，您会看到此答案https://stackoverflow.com/a/25632407/1270400此答案仅适用于可见行。但我必须在不可见和可见的行中添加徽章。@ pomber提供了一个提示我无法理解。

我该怎么做这个过程？我需要一个例子。

Answer 1

您不应该尝试直接修改listview的子元素。而是修改适配器，以便根据某些条件显示徽章。

然后，修改适配器的基础数据（并在适配器上调用notifyDatasetChanged()），listview将自行重绘。

例如，将您的适配器视为由Song对象列表支持。在getView()中，如果((Song) get item(position)).isFavourited()返回true，则可以显示徽章。

要在列表中显示第n首歌曲的徽章，您需要修改列表（songs.get(n).favourite()）并致电adapter.notifyDatasetChanged()。

使用更详细但不详尽的完整示例进行编辑。请注意评论和TODO：

import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ListAdapter;

import java.util.ArrayList;
import java.util.List;

public class Test  {

    public static void test() {
        List<Song> songsList = new ArrayList<Song>();
        songsList.add(new Song("Generic Song Title", false));
        songsList.add(new Song("Another Song Title", false));
        songsList.add(new Song("A Third Song Title", false));
        Songs songs = new Songs(songsList);

        ListAdapter songsAdapter = new SongsAdapter(songs);
        // TODO: ListView.setAdapter(songsAdapter)

        /*
        When you want to change the visibility on a badge of a given song,
        do NOT modify the view by trying to access it from the ListView
        using ListView.getChildAt(int).

        Update the data, and give it to your adapter, as follows:
         */
        List<Song> anotherSongsListWithFavourites = new ArrayList<Song>();
        songsList.add(new Song("Generic Song Title", false));
        songsList.add(new Song("Another Song Title", true));
        songsList.add(new Song("A Third Song Title", true));
        Songs modifiedSongs = new Songs(anotherSongsListWithFavourites);
        ((SongsAdapter) songsAdapter).updateSongs(modifiedSongs);
    }

    public static void test2_updateExistingSongCollection() {
        List<Song> songsList = new ArrayList<Song>();
        songsList.add(new Song("Generic Song Title", false));
        songsList.add(new Song("Another Song Title", false));
        songsList.add(new Song("A Third Song Title", false));
        Songs songs = new Songs(songsList);

        ListAdapter songsAdapter = new SongsAdapter(songs);
        // TODO: ListView.setAdapter(songsAdapter)

        /*
        Now we update the existing Songs object. The adapter's reference is 
        still pointing to it, so that data will change too, but the adapter
        won't know. This means the data will not immediately update on screen,
        unless the user scrolls up/down OR unless we tell the adapter to
        call `notifyDatasetChanged()` which we'd have to expose another method
        for because it's a `protected` method (not shown).
         */
        songs.get(0).isFavourite = true;
    }

    private static class Song {

        public final String songName;
        // not final because we're grossly modifying this for the example in test2
        public boolean isFavourite;

        private Song(String songName, boolean isFavourite) {
            this.songName = songName;
            this.isFavourite = isFavourite;
        }

    }

    private static class Songs {

        private final List<Song> songs;

        public Songs(List<Song> songs) {
            this.songs = songs;
        }

        public Song get(int position) {
            return songs.get(position);
        }

        public int size() {
            return songs.size();
        }

    }

    private static class SongsAdapter extends BaseAdapter {

        private Songs songs;

        private SongsAdapter(Songs songs) {
            this.songs = songs;
        }

        /*
            Update the dataset, and then pass the new data to the adapter.
            You could update an individual song, but I wouldn't recommmend it.
            This adapter's responsibility is to take a Songs object map each one
            to a View - it shouldn't have to deal with MODIFYING the dataset.

            Note, the `notifyDataSetChanged()`. This tells the ListView to ask
            the adapter for new views (with updated data).
         */
        public void updateSongs(Songs songs) {
            this.songs = songs;
            notifyDataSetChanged();
        }

        @Override
        public int getCount() {
            return songs.size();
        }

        @Override
        public Song getItem(int position) {
            return songs.get(position);
        }

        @Override
        public long getItemId(int position) {
            // we won't support stable IDs for this example
            return 0;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            View view = convertView;
            if (view == null) {
                view = createNewView();
            }
            update(view, songs.get(position));
            return view;
        }

        private View createNewView() {
            // TODO: create a new instance of your view and return it
            return null;
        }

        private void update(View view, Song song) {
            // TODO: update the rest of the view
            if (song.isFavourite) {
                // TODO: show badge on view
            } else {
                // TODO: hide the badge on view
            }
        }

    }

}

适配器更新不可见行

1 个答案: