Android HTML ImageGetter 作为 AsyncTask

Question

好的，我正在为这个而失去理智。我的程序中有一个解析 HTML 的方法。我想包含内联图像，我的印象是使用 Html.fromHtml(string, Html.ImageGetter, Html.TagHandler) 将允许这种情况发生。

由于 Html.ImageGetter 没有实现，由我来编写。但是，由于将URL解析成Drawables需要网络访问，所以我不能在主线程上这样做，所以它必须是一个AsyncTask。我想。

但是，当您将 ImageGetter 作为参数传递给 Html.fromHtml 时，它使用的 getDrawable 方法必须被覆盖。因此无法调用触发 doInBackground 方法的整个 ImageGetter.execute 交易，因此无法真正实现异步。

我是不是完全错了，或者更糟的是，这不可能吗？谢谢

Answer 1

我做了一些与你想做的事情非常相似(我认为)的事情。那时我需要做的是解析 HTML 并将其设置回 TextView，我还需要使用 Html.ImageGetter 并且在主线程上获取图像时遇到同样的问题。

我基本做的步骤:

• 为Drawable创建自己的子类，方便重绘，我称之为URLDrawable
• 返回Html.ImageGetter
的 getDrawable方法中的 URLDrawable
• 一旦调用 onPostExecute，我就重绘 Spanned 结果的容器

现在 URLDrawable 的代码如下

public class URLDrawable extends BitmapDrawable {
    // the drawable that you need to set, you could set the initial drawing
    // with the loading image if you need to
    protected Drawable drawable;

    @Override
    public void draw(Canvas canvas) {
        // override the draw to facilitate refresh function later
        if(drawable != null) {
            drawable.draw(canvas);
        }
    }
}

很简单，我只是重写了 draw，所以它会在 AsyncTask 完成后选择我在那里设置的 Drawable。

下面的类是Html.ImageGetter的实现，是从AsyncTask获取图片并更新图片的类

public class URLImageParser implements ImageGetter {
    Context c;
    View container;

    /***
     * Construct the URLImageParser which will execute AsyncTask and refresh the container
     * @param t
     * @param c
     */
    public URLImageParser(View t, Context c) {
        this.c = c;
        this.container = t;
    }

    public Drawable getDrawable(String source) {
        URLDrawable urlDrawable = new URLDrawable();

        // get the actual source
        ImageGetterAsyncTask asyncTask = 
            new ImageGetterAsyncTask( urlDrawable);

        asyncTask.execute(source);

        // return reference to URLDrawable where I will change with actual image from
        // the src tag
        return urlDrawable;
    }

    public class ImageGetterAsyncTask extends AsyncTask<String, Void, Drawable>  {
        URLDrawable urlDrawable;

        public ImageGetterAsyncTask(URLDrawable d) {
            this.urlDrawable = d;
        }

        @Override
        protected Drawable doInBackground(String... params) {
            String source = params[0];
            return fetchDrawable(source);
        }

        @Override
        protected void onPostExecute(Drawable result) {
            // set the correct bound according to the result from HTTP call
            urlDrawable.setBounds(0, 0, 0 + result.getIntrinsicWidth(), 0 
                    + result.getIntrinsicHeight()); 

            // change the reference of the current drawable to the result
            // from the HTTP call
            urlDrawable.drawable = result;

            // redraw the image by invalidating the container
            URLImageParser.this.container.invalidate();
        }

        /***
         * Get the Drawable from URL
         * @param urlString
         * @return
         */
        public Drawable fetchDrawable(String urlString) {
            try {
                InputStream is = fetch(urlString);
                Drawable drawable = Drawable.createFromStream(is, "src");
                drawable.setBounds(0, 0, 0 + drawable.getIntrinsicWidth(), 0 
                        + drawable.getIntrinsicHeight()); 
                return drawable;
            } catch (Exception e) {
                return null;
            } 
        }

        private InputStream fetch(String urlString) throws MalformedURLException, IOException {
            DefaultHttpClient httpClient = new DefaultHttpClient();
            HttpGet request = new HttpGet(urlString);
            HttpResponse response = httpClient.execute(request);
            return response.getEntity().getContent();
        }
    }
}

最后，下面是演示工作原理的示例程序:

String html = "Hello " +
"<img src='http://www.gravatar.com/avatar/" + 
"f9dd8b16d54f483f22c0b7a7e3d840f9?s=32&d=identicon&r=PG'/>" +
" This is a test " +
"<img src='http://www.gravatar.com/avatar/a9317e7f0a78bb10a980cadd9dd035c9?s=32&d=identicon&r=PG'/>";

this.textView = (TextView)this.findViewById(R.id.textview);
URLImageParser p = new URLImageParser(textView, this);
Spanned htmlSpan = Html.fromHtml(html, p, null);
textView.setText(htmlSpan);