快速将图像 url 转换为位图

Converting image url to bitmap quickly(快速将图像 url 转换为位图)

问题描述

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.

I need to display the list of images from api in the list page. For that i used two approaches.

第一种方法:
通过将url转换为字节数组，然后将其转换为位图.请找到下面的代码..

First Approach:
By converting the url to byte array and then converting it into bitmap.Please find the below code..

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:

Converting byte array to bitmap:

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

Second Approach:
Image scaling based on height and width

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);
        }
    }
}

这两种方法都使 APP 非常慢.所以这是我的问题..

Both approaches making the APP very slow. So here is my questions..

1. 如何快速将 url 转换为位图而不会使应用变慢?

1. How can i quickly convert the url into bitmap without making the app slow?

其他应用程序(如 Flipcart)如何显示 1000 多张图像，没有任何缓慢或挂起?

How the other apps(like flipcart) displaying the 1000>s of images, without any slow or hang?

请指导以获得答案.

推荐答案

有一个名为 Picasso 的库.它可以有效地从 url 加载图像.它还可以从文件中加载图像.你想做的，写一行代码.

There is a library named Picasso. which can efficiently load images from url. it can also load image from the File. all you wanted to do , write a line of code.

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; 

它还可以缓存你的图片，所以加载的图片下次可以更快地加载而不会浪费数据.

It can also cache your image, so the loaded image could be able to load faster on the next time without wasting the data.

毕加索提供了更多选项.这里是文档

There are many more options available in Picasso. Here is the documentation

如果您需要圆角位图

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

RoundedTransformation.java

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";
    }
}

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