Question

我有这段小代码，我想实现这个目标：程序应该从链接图像设置壁纸。

ImgDownload：

public class ImgDownload extends AsyncTask {
        private String requestUrl;
        private ImageView view;
        private Bitmap pic;

        private ImgDownload(String requestUrl, ImageView view) {
            this.requestUrl = requestUrl;
            this.view = view;
        }

        @Override
        protected Object doInBackground(Object... objects) {
            try {
                URL url = new URL(requestUrl);
                URLConnection conn = url.openConnection();
                pic = BitmapFactory.decodeStream(conn.getInputStream());
            } catch (Exception ex) {
            }
            return null;
        }

        @Override
        protected void onPostExecute(Object o) {
            view.setImageBitmap(pic);
        }
    }

主要

public class MainActivity extends Activity {

    private ImageView img;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        img= (ImageView)findViewById(R.id.img);

//!!!! This is where I am stuck :)
        Object s = new ImgDownload("http://images1.wikia.nocookie.net/__cb20120402213849/masseffect/images/4/42/Uncharted_Worlds_Codex_Image.jpg",img );
    }



    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

}

如何在mainActivity中实例化/创建这个类，所以它可以从链接下载img？任何帮助建议，想法，将不胜感激：）

Answer 1

你像这样执行这个AsyncTask：

ImgDownload downloader = new ImgDownload("http://images1.wikia.nocookie.net/__cb20120402213849/masseffect/images/4/42/Uncharted_Worlds_Codex_Image.jpg",img);
downloader.execute();

但我不建议使用你的代码，因为它会产生内存泄漏。例如，尝试在下载图像时旋转设备。我保证你的申请会崩溃。加上AsyncTask是一个通用类。您可以使用它来使您的代码更简单。这是我改进的图像下载任务：

public class ImgDownload extends AsyncTask<Void, Void, Bitmap> { // Use Generics
    private final String requestUrl;
    private final WeakReference<ImageView> imageViewReference; // Use WeakReference to prevent memory leaks

    public ImgDownload(String requestUrl, ImageView view) {
        this.requestUrl = requestUrl;
        this.imageViewReference = new WeakReference<ImageView>(view);
    }

    @Override
    protected Bitmap doInBackground(Void... objects) {
        try {
            URL url = new URL(requestUrl);
            URLConnection conn = url.openConnection();
            return BitmapFactory.decodeStream(conn.getInputStream()); // Return bitmap instead of using global variable
        } catch (Exception ex) {
        }
        return null;
    }

    @Override
    protected void onPostExecute(Bitmap bitmap) {
        ImageView imageView = imageViewReference.get();
        if(imageView != null && bitmap != null) { // Check if image or ImageView are null
            imageView.setImageBitmap(bitmap);
        }
    }
}

Answer 2

new ImgDownload("http://images1.wikia.nocookie.net/__cb20120402213849/masseffect/images/4/42/Uncharted_Worlds_Codex_Image.jpg", MainActivity.img).execute();

下载并设置壁纸

2 个答案: