安卓：从Web与AsyncTask的加载图像 [英] Android : Loading an image from the Web with Asynctask

问题描述

我如何替换code时的AsyncTask以下几行？ 你如何找回从AsyncTask的位图？谢谢你。

How do I replace the following lines of code with an Asynctask ? How do you "get back" the Bitmap from the Asynctask ? Thank you.

ImageView mChart = (ImageView) findViewById(R.id.Chart);
String URL = "http://www...anything ...";

mChart.setImageBitmap(download_Image(URL));

public static Bitmap download_Image(String url) {

        //---------------------------------------------------
        Bitmap bm = null;
        try {
            URL aURL = new URL(url);
            URLConnection conn = aURL.openConnection();
            conn.connect();
            InputStream is = conn.getInputStream();
            BufferedInputStream bis = new BufferedInputStream(is);
            bm = BitmapFactory.decodeStream(bis);
            bis.close();
            is.close();
        } catch (IOException e) {
            Log.e("Hub","Error getting the image from server : " + e.getMessage().toString());
        } 
        return bm;
        //---------------------------------------------------

    }

我想过这样的事情：

I thought about something like this :

替换：

mChart.setImageBitmap(download_Image(graph_URL));

通过这样的：

by something like :

mChart.setImageBitmap(new DownloadImagesTask().execute(graph_URL));

和

public class DownloadImagesTask extends AsyncTask<String, Void, Bitmap> {

@Override
protected Bitmap doInBackground(String... urls) {
    return download_Image(urls[0]);
}

@Override
protected void onPostExecute(Bitmap result) {
    mChart.setImageBitmap(result);              // how do I pass a reference to mChart here ?
}


private Bitmap download_Image(String url) {
    //---------------------------------------------------
    Bitmap bm = null;
    try {
        URL aURL = new URL(url);
        URLConnection conn = aURL.openConnection();
        conn.connect();
        InputStream is = conn.getInputStream();
        BufferedInputStream bis = new BufferedInputStream(is);
        bm = BitmapFactory.decodeStream(bis);
        bis.close();
        is.close();
    } catch (IOException e) {
        Log.e("Hub","Error getting the image from server : " + e.getMessage().toString());
    } 
    return bm;
    //---------------------------------------------------
}


}

但我如何通过引用mChart在onPostExecute（位图结果）??? 我需要以某种方式将URL传递？ 我想换掉我所有的行code：

but How do I pass a reference to mChart in onPostExecute(Bitmap result) ??? Do I need to pass it with the URL in some way ? I would like to replace all my lines of code :

mChart1.setImageBitmap(download_Image(URL_1));
mChart2.setImageBitmap(download_Image(URL_2));

使用类似的东西......但在AsyncTask的方式！

with something similar ... but in Asynctask way !

mChart1.setImageBitmap(new DownloadImagesTask().execute(graph_URL_1));
mChart2.setImageBitmap(new DownloadImagesTask().execute(graph_URL_2));

对此有一个简单的解决方案？ 我能得到什么错在这里？

Is there an easy solution for this ? Do I get something wrong here ?

推荐答案

如果没有充分的理由对自己下载的图像，然后我会建议使用的毕加索。

If there is no good reason to download the image yourself then I would recommend to use Picasso.

毕加索可以节省您所有的问题，下载，设置和缓存的图像。 需要一个简单的例子，整个code是：

Picasso saves you all the problems with downloading, setting and caching images. The whole code needed for a simple example is:

Picasso.with(context).load(url).into(imageView);

如果你真的想要做的一切你自己用我下面年长的答案。

If you really want to do everything yourself use my older answer below.

如果图像不那么大，你可以只使用一个匿名类的异步任务。 这将是这样的：

If the image is not that big you can just use an anonymous class for the async task. This would like this:

ImageView mChart = (ImageView) findViewById(R.id.imageview);
String URL = "http://www...anything ...";

mChart.setTag(URL);
new DownloadImageTask.execute(mChart);

任务等级：

public class DownloadImagesTask extends AsyncTask<ImageView, Void, Bitmap> {

ImageView imageView = null;

@Override
protected Bitmap doInBackground(ImageView... imageViews) {
    this.imageView = imageViews[0];
    return download_Image((String)imageView.getTag());
}

@Override
protected void onPostExecute(Bitmap result) {
    imageView.setImageBitmap(result);
}


private Bitmap download_Image(String url) {
   ...
}

隐藏在标签中的URL是有点棘手，但它会在调用的类更好，如果你有很多要填补这样imageviews的。它还帮助，如果你正在使用一个ListView里面的ImageView的，你要知道，如果ImageView的是图像的下载过程中循环使用。

Hiding the URL in the tag is a bit tricky but it looks nicer in the calling class if you have a lot of imageviews that you want to fill this way. It also helps if you are using the ImageView inside a ListView and you want to know if the ImageView was recycled during the download of the image.

我写的，如果你的图像并不大，因为这将导致有一个隐含的指针底层活动造成的垃圾收集，直到任务完成保持整个活动在内存中的任务。如果用户移动到您的应用程序的另一个屏幕，而位图下载该内存不能被释放，这可能使您的应用程序和整个系统变慢。

I wrote if you Image is not that big because this will result in the task having a implicit pointer to the underlying activity causing the garbage collector to hold the whole activity in memory until the task is finished. If the user moves to another screen of your app while the bitmap is downloading the memory can't be freed and it may make your app and the whole system slower.

这篇关于安卓：从Web与AsyncTask的加载图像的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！