java - 如何在Android中的AsyncTask中应用此代码？

Question

我有一个从文件路径解码图像的代码，但是，它占用了太多的空间并在主线程中进行处理。我不知道如何将其改编成 AsyncTask 类。

Bitmap bitmap;
BitmapFactory.Options bitmapOptions = new BitmapFactory.Options();
SetBitmapOptions(bitmapOptions);
bitmap = BitmapFactory.decodeFile(f.getAbsolutePath(), bitmapOptions);
ByteArrayOutputStream stream = new ByteArrayOutputStream();
bitmap.compress(Bitmap.CompressFormat.JPEG, 100, stream);
byte[] byte_arr = stream.toByteArray();
image_str = Base64.encodeToString(byte_arr, Base64.DEFAULT);
viewImage.setImageBitmap(bitmap);

我想使用 Android Developer 中找到的代码

http://developer.android.com/training/displaying-bitmaps/process-bitmap.html

代码

class BitmapWorkerTask extends AsyncTask<Integer, Void, Bitmap> {
    private final WeakReference<ImageView> imageViewReference;
    private int data = 0;

public BitmapWorkerTask(ImageView imageView) {
    // Use a WeakReference to ensure the ImageView can be garbage collected
    imageViewReference = new WeakReference<ImageView>(imageView);
}

// Decode image in background.
@Override
protected Bitmap doInBackground(Integer... params) {
    data = params[0];
    return decodeSampledBitmapFromResource(getResources(), data, 100, 100));
}

// Once complete, see if ImageView is still around and set bitmap.
@Override
protected void onPostExecute(Bitmap bitmap) {
    if (imageViewReference != null && bitmap != null) {
        final ImageView imageView = imageViewReference.get();
        if (imageView != null) {
            imageView.setImageBitmap(bitmap);
        }
    }
}
}

我不知道 resId 是什么以及如何将我的位图变量传递给它

Answer 1

您可以通过Async_BitmapWorkerTask类中的构造函数传递参数。您可能想阅读更简单的 AsyncTask 示例，例如 example .

someMethod() {
    Bitmap bitmap;
    BitmapFactory.Options bitmapOptions = new BitmapFactory.Options();
    SetBitmapOptions(bitmapOptions);
    bitmap = BitmapFactory.decodeFile(f.getAbsolutePath(), bitmapOptions);

    // Run the AsyncTask with the bitMap and imageview as a parameters
    new Async_BitmapWorkerTask(bitmap, imageView).execute();
}

class Async_BitmapWorkerTask extends AsyncTask<Integer, Void, String> {
    private final Bitmap bitmap;
    private final ImageView imageView;
    private int data = 0;

    // Constructor
    public Async_BitmapWorkerTask(Bitmap bitmap, ImageView imageView) {
        this.bitmap = bitmap;
        this.imageView = imageView;
    }

    // Compress and Decode image in background.
    @Override
    protected String doInBackground(Integer... params) {

        ByteArrayOutputStream stream = new ByteArrayOutputStream();
        bitmap.compress(Bitmap.CompressFormat.JPEG, 100, stream);
        byte[] byte_arr = stream.toByteArray();
        String image_str = Base64.encodeToString(byte_arr, Base64.DEFAULT);

        return image_str;
    }

    // This method is run on the UI thread
    @Override
    protected void onPostExecute(String string) {
        if (imageView != null && bitmap != null) {
            imageView.setImageBitmap(bitMap);
        }
    }
}