android - 如何为大图像实现Android ImageGetter？

Question

我正在将 HTML 显示到 TextView 中:

    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'/>";

    Spanned htmlSpan = Html.fromHtml(html, imageParser, null);
    textView.setText(htmlSpan);

下面的 ImageParser 完成了这项工作:

  public class URLImageParser implements Html.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();
    }
}

但它不适用于更大的图像。不起作用的String如下:

  String html = "Hello " +
            "<img src='http://darwin.suav.biz/image/data/produse/Tablete/Apple/Ipad 4/hero_slide1.png" +
            " This is a test " +
            "<img src='http://www.gravatar.com/avatar/a9317e7f0a78bb10a980cadd9dd035c9?s=32&d=identicon&r=PG'/>";

它因以下错误而崩溃:

java.lang.NullPointerException
        at md.darwin.catalog.manager.URLImageParser$ImageGetterAsyncTask$1.run(URLImageParser.java:70)
        at android.os.Handler.handleCallback(Handler.java:733)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:5038)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
        at dalvik.system.NativeStart.main(Native Method)

URLImageParser.java:70 是:

              urlDrawable.setBounds(0, 0, result.getIntrinsicWidth(), result.getIntrinsicHeight());

我也尝试过使用 Picasso，方法在这里:https://github.com/aegis123/Bettyskitchen-app/blob/master/BettysKitchen-app/src/main/java/com/bettys/kitchen/recipes/app/Utils/ImageGetter.java

但我得到错误(没有崩溃):无法解码流

有谁知道更大的图像会出现什么问题？为什么在 onPostExecute 中会是 Null？

Answer 1

您必须记录并检查 catch(Exception e) 捕获的内容。很明显那里有一个异常，fetchDrawable() 正在返回 null。但是你没有正确地分析/检查它，没有办法知道那里出了什么问题。

Thank you. This helped. I did not even suppose my imageURL was bad. Now everything works with InputStream with bigger images.

很高兴它起作用了。如果我是你，我会应用 Picasso 而不会使用 AsyncTask。 Picasso 线程比 AsyncTask 更精细，它有 2 级(RAM n 磁盘)缓存。