Android HTML ImageGetter as AsyncTask

Question

好吧,我对这个失去了理智.我的程序中有一个解析HTML的方法.我想要包含内嵌图像,我的印象是使用Html.fromHtml(字符串,Html.ImageGetter,Html.TagHandler)将允许这种情况发生.

由于Html.ImageGetter没有实现,所以由我来编写一个.但是,由于将URL解析为Drawables需要网络访问,我不能在主线程上执行此操作,因此它必须是AsyncTask.我认为.

但是,当您将ImageGetter作为参数传递给Html.fromHtml时,它使用必须重写的getDrawable方法.因此无法调用触发doInBackground方法的整个ImageGetter.execute事务,因此无法实际实现此异步.

我是否完全错了,或者更糟糕的是,这是不可能的？谢谢

Answer 1

我做了一些非常类似的事情(我想),你想做什么.那时我需要做的是解析HTML并将其设置回TextView,我也需要使用Html.ImageGetter它并在主线程上获取图像时遇到同样的问题.

我基本上做的步骤:

• 为Drawable创建我自己的子类以便于重绘,我称之为URLDrawable
• 返回URLDrawablein getDrawable方法Html.ImageGetter
• 一旦onPostExecute调用,我重绘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,我只是覆盖draw所以它会选择AsyncTask完成后我在那里设置的Drawable.

以下类是Html.ImageGetter从图像中获取图像AsyncTask并更新图像的实现

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,下面是演示如何工作的示例程序:

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);

Answer 2

挺棒的.但是,不推荐使用DefaultHttpClient类型.在获取方法上尝试这个:

private InputStream fetch(String urlString) throws MalformedURLException, IOException {

        URL url = new URL(urlString);
        HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
        InputStream stream = urlConnection.getInputStream();

        return stream;

    }