为列表视图调用并实例化适配器

Question

list_item.java

  public class List_Items extends ListActivity{

 public void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
       setContentView(R.layout.list_item);


       ListView lv = (ListView) this.findViewById(android.R.id.list);

       lv.setAdapter((ListAdapter) new ImageAndTextListAdapter(this, xxx));


      Button btn=(Button) findViewById(R.id.button_sync);
      btn.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
                    }
                    // code here
                }
              }

ImageAndTextListAdapter.java

    public class ImageAndTextListAdapter extends ArrayAdapter<ImageAndText> {

//   new method
    private ListView listView;
    private AsyncImageLoader asyncImageLoader;

//constructor
public ImageAndTextListAdapter(Activity activity, List<ImageAndText> imageAndTexts) {
    super(activity, 0, imageAndTexts);

    //new method
    this.listView = listView;
    asyncImageLoader = new AsyncImageLoader();
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    Activity activity = (Activity) getContext();
  //  ......

}

}

ImageAndText.java

   public class ImageAndText {
    private String imageUrl;
   private String text;

public ImageAndText(String imageUrl, String text) {
    this.imageUrl = imageUrl;
    this.text = text;
}
public String getImageUrl() {
    return imageUrl;
}
public String getText() {
    return text;
}

}

AsyncImageLoader.java

  public class AsyncImageLoader {
  private HashMap<String, SoftReference<Drawable>> imageCache;
  HashMap<String, SoftReference<Drawable>> drawableMap = new HashMap<String,          SoftReference<Drawable>>();


public AsyncImageLoader() {
    //HashMap<String, SoftReference<Drawable>> drawableMap = new HashMap<String, SoftReference<Drawable>>();
}

public Drawable loadDrawable(final String imageUrl, final ImageCallback imageCallback) {

    if (drawableMap.containsKey(imageUrl)) {
        SoftReference<Drawable> softReference = imageCache.get(imageUrl);
        Drawable drawable = softReference.get();
        if (drawable != null) {
            return drawable;
        }
    }
    final Handler handler = new Handler() {
        @Override
        public void handleMessage(Message message) {
            imageCallback.imageLoaded((Drawable) message.obj, imageUrl);
        }
    };

    //this is the new thread that download the image from url
    new Thread() {
        @Override
        public void run() {
            Drawable drawable = loadImageFromUrl(imageUrl);
            imageCache.put(imageUrl, new SoftReference<Drawable>(drawable));
            Message message = handler.obtainMessage(0, drawable);
            handler.sendMessage(message);
        }
    }.start();
    return null;
}

public static Drawable loadImageFromUrl(String url) {
      InputStream inputStream;
      try {
          inputStream = new URL(url).openStream();
      } catch (IOException e) {
          throw new RuntimeException(e);
      }
      return Drawable.createFromStream(inputStream, "src");
}

public interface ImageCallback {
    public void imageLoaded(Drawable imageDrawable, String imageUrl);
}

}

在此示例中，list_item.java 的 listview 最初是空的，它将调用 ImageAndTextListAdapter，后者将调用 Web url 来提供 listview 行数据图像和文本动态。

我的问题是如何调用适配器， lv.setAdapter((ListAdapter) new ImageAndTextListAdapter(this, xxx)); xxx 应该是什么？我可以只做一个 xxx=List imageAndTexts 列表 ImageAndText 类，但这不是重复 ImaheAndTextListAdapter 构造函数中的内容吗？

其次，我应该在点击例程中提供什么， public void onClick(View v) { } // 代码在这里 } } 在 list_item 中。
我的目标是按下按钮，这将启动 adpater 提供所有必要数据的操作。

Answer 1

从 ImageAndTextListAdapter 适配器中，xxx 应该是一个列表。

您的适配器采用“活动”和“列表”两个参数。

因此，您应该创建一个列表，并创建 ImageAndText 类的对象以添加到列表中，如下所示。

ImageAndText image = new ImageAndText("url","Test");
 List<ImageAndText>text;
 text.add(image); //Add the Object of ImageAndText
 ListView lv = (ListView) findViewById(android.R.id.list);

 //Here i supply the adapter with the text list created.
 lv.setAdapter((ListAdapter)new ImageAndTextListAdapter(Main.this, text));