快速將圖片網址轉換為位圖

Question

我需要在列表頁面中顯示來自api的圖像列表。 為此，我使用了兩種方法。

第一種方法：
通過將url轉換為byte數組然后將其轉換為bitmap。請找到以下代碼..

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();

將字節數組轉換為位圖：

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

第二種方法：
基於高度和寬度的圖像縮放

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);
        }
    }
}

兩種方法都使APP非常慢。 所以這是我的問題..

1. 如何在不使應用程序變慢的情況下快速將網址轉換為位圖？

2. 其他應用程序（如flipcart）如何顯示1000個圖像，沒有任何緩慢或掛起？

   請指導以獲得答案。

Answer 1

有一個名為畢加索的圖書館。 它可以有效地從網址加載圖像。 它還可以從文件中加載圖像。 所有你想做的，寫一行代碼。

例

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

它還可以緩存您的圖像，因此加載的圖像可以在下次加載時更快，而不會浪費數據。

畢加索還有更多選擇。 這是文檔

如果你需要圓角的位圖

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

有一些開源庫專注於將圖像加載到ImageView 。 以Universal-image-loader為例，它非常易於使用，如：

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

要么：

// 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
    }
});

要么：

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

以Volley為例，您可以像這樣使用它：

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);
    //指定圖片允許的最大寬度和高度
    //imageLoader.get("http://developer.android.com/images/home/aw_dac.png",listener, 200, 200);
}

這些庫被廣泛使用，更重要的是，它們是開源的。 不需要反復實現這樣的功能。

Answer 3

試試這個

希望這對你有幫助。