Question

我需要在列表页面中显示来自api的图像列表。为此，我使用了两种方法。

第一种方法：
通过将url转换为byte数组然后将其转换为bitmap。请找到以下代码..

URL imageUrl = new URL(url);
URLConnection ucon = imageUrl.openConnection();

InputStream is = ucon.getInputStream();
BufferedInputStream bis = new BufferedInputStream(is);

ByteArrayBuffer baf = new ByteArrayBuffer(500);
int current = 0;
while ((current = bis.read()) != -1) {
     /* This approach slowdown the process*/
     baf.append((byte) current);
}

byte[] img_ary= baf.toByteArray();

将字节数组转换为位图：

ByteArrayInputStream imageStream = new ByteArrayInputStream(
                    imgUrl);
Bitmap theImage = BitmapFactory.decodeStream(imageStream);

第二种方法：
基于高度和宽度的图像缩放

private static final String TAG_iamge = "Image";
private static final int IO_BUFFER_SIZE = 4 * 1024;

public static Bitmap loadBitmap(String url) {
    Bitmap bitmap = null;
    InputStream in = null;
    BufferedOutputStream out = null;

    try {
        in = new BufferedInputStream(new URL(url).openStream(),
                IO_BUFFER_SIZE);

        final ByteArrayOutputStream dataStream = new ByteArrayOutputStream();
        out = new BufferedOutputStream(dataStream, IO_BUFFER_SIZE);
        copy(in, out);
        out.flush();

        final byte[] data = dataStream.toByteArray();
        BitmapFactory.Options options = new BitmapFactory.Options();

        options.inJustDecodeBounds = true;
        options.inDither = false;
        options.inPurgeable = true;
        options.inInputShareable = true;

        bitmap = BitmapFactory.decodeByteArray(data, 0, data.length,
                options);

        final int height = options.outHeight;
        final int width = options.outWidth;
        int inSampleSize = 1;
        int reqHeight = 500;
        int reqWidth = 500;

        if (height > reqHeight || width > reqWidth) {

            final int halfHeight = height / 2;
            final int halfWidth = width / 2;

            // Calculate the largest inSampleSize value that is a power of 2
            // and keeps both
            // height and width larger than the requested height and width.
            while ((halfHeight / inSampleSize) > reqHeight
                    && (halfWidth / inSampleSize) > reqWidth) {
                inSampleSize *= 2;
            }
        }

        int scale = inSampleSize;

        BitmapFactory.Options o2 = new BitmapFactory.Options();
        o2.inSampleSize = scale;
        o2.inDither = false;
        o2.inPurgeable = true;
        o2.inInputShareable = true;
        return BitmapFactory.decodeByteArray(data, 0, data.length, o2);
    } catch (Exception e) {
        Log.e(TAG_iamge, "Could not load Bitmap from: " + url);
    } finally {
        closeStream(in);
        closeStream(out);
    }

    return bitmap;
}

private static void copy(InputStream in, OutputStream out)
        throws IOException {
    byte[] b = new byte[IO_BUFFER_SIZE];
    int read;
    while ((read = in.read(b)) != -1) {
        out.write(b, 0, read);
    }
}

private static void closeStream(Closeable stream) {
    if (stream != null) {
        try {
            stream.close();
        } catch (IOException e) {
            android.util.Log.e("", "Could not close stream", e);
        }
    }
}

两种方法都使APP非常慢。所以这是我的问题..

如何在不让应用程序变慢的情况下快速将网址转换为位图？
其他应用程序（如flipcart）如何显示1000＆s;的图像，没有任何缓慢或挂起？

请指导以获得答案。

Answer 1

有一个名为Picasso的图书馆。它可以有效地从网址加载图像。它还可以从文件中加载图像。所有你想做的，写一行代码。

示例

Picasso.with(context) //Context .load("http://i.imgur.com/DvpvklR.png") //URL/FILE .into(imageView)//an ImageView Object to show the loaded image;

它还可以缓存您的图像，因此加载的图像可以在下次加载时更快，而不会浪费数据。

毕加索还有更多选择。 Here is the documentation

如果您需要圆角的位图

Picasso.with(mContext) .load("your-image-url-or-file-or-drawable") .transform(new RoundedTransformation(200, 0)) .fit() .into(imageView);

RoundedTransformation.java

import android.graphics.Bitmap; import android.graphics.Bitmap.Config; import android.graphics.BitmapShader; import android.graphics.Canvas; import android.graphics.Paint; import android.graphics.RectF; import android.graphics.Shader; // enables hardware accelerated rounded corners // original idea here : http://www.curious-creature.org/2012/12/11/android-recipe-1-image-with-rounded-corners/ public class RoundedTransformation implements com.squareup.picasso.Transformation { private final int radius; private final int margin; // dp // radius is corner radii in dp // margin is the board in dp public RoundedTransformation(final int radius, final int margin) { this.radius = radius; this.margin = margin; } @Override public Bitmap transform(final Bitmap source) { final Paint paint = new Paint(); paint.setAntiAlias(true); paint.setShader(new BitmapShader(source, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP)); Bitmap output = Bitmap.createBitmap(source.getWidth(), source.getHeight(), Config.ARGB_8888); Canvas canvas = new Canvas(output); canvas.drawRoundRect(new RectF(margin, margin, source.getWidth() - margin, source.getHeight() - margin), radius, radius, paint); if (source != output) { source.recycle(); } return output; } @Override public String key() { return "rounded"; } }

Answer 2

有开源库专注于将图像加载到ImageView。以universal-image-loader为例，它非常易于使用，如：

// Load image, decode it to Bitmap and display Bitmap in ImageView (or any other view 
//  which implements ImageAware interface)
imageLoader.displayImage(imageUri, imageView);

或：

// Load image, decode it to Bitmap and return Bitmap to callback
imageLoader.loadImage(imageUri, new SimpleImageLoadingListener() {
    @Override
    public void onLoadingComplete(String imageUri, View view, Bitmap loadedImage) {
        // Do whatever you want with Bitmap
    }
});

或：

// Load image, decode it to Bitmap and return Bitmap synchronously
Bitmap bmp = imageLoader.loadImageSync(imageUri);

以Volley为例，您可以像这样使用它：

public void displayImg(View view){
    ImageView imageView = (ImageView)this.findViewById(R.id.image_view);
    RequestQueue mQueue = Volley.newRequestQueue(getApplicationContext()); 

    ImageLoader imageLoader = new ImageLoader(mQueue, new BitmapCache());

    ImageListener listener = ImageLoader.getImageListener(imageView,R.drawable.default_image, R.drawable.default_image);
    imageLoader.get("http://developer.android.com/images/home/aw_dac.png", listener);
    //指定图片允许的最大宽度和高度
    //imageLoader.get("http://developer.android.com/images/home/aw_dac.png",listener, 200, 200);
}

这些库被广泛使用，更重要的是，它们是开源的。不需要反复实现这样的功能。

Answer 3

Try this

希望这对你有帮助。

快速将图片网址转换为位图

3 个答案: