Volley ImageLoader加载本地图片特别版

来源：互联网发布：自考计算机本科知乎编辑：程序博客网时间：2024/06/05 00:44

最近项目中用到gridView显示图片，一开始自然而然的就想到显示图片用Android-Universal-Image-Loader,结果在gridview中却发现不能显示本地图片，试了多次还是不知道什么原因；如果布局文件中单独的一个imageview调用imageLoader却可以正常显示。说明我的imageLoader配置没错，很有可能这个框架和gridview结合并且加载本地图片有问题。所以我就打算自己写一个工具专门用来加载本地图片。动手之前突然想到google的volley也有一个加载图片的工具类，只不过volley只适合加载网络图片。所以就想到借用volley的图片解析方法自己写一个图片加载工具，哈哈，是不是很好。

代码呈上：

package com.hai.utils;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.widget.ImageView;/** * Created by 黄海 on 2016/1/20. */public class ImageLoader {    /**     * 解析本地图片     *     * @param url           本地图片文件目录     * @param mMaxWidth     * @param mMaxHeight     * @param mScaleType     * @param mDecodeConfig     * @return     */    public static Bitmap parseFile(String url, int mMaxWidth, int mMaxHeight, ImageView.ScaleType mScaleType, Bitmap.Config mDecodeConfig) {//        byte[] data = response.data;        BitmapFactory.Options decodeOptions = new BitmapFactory.Options();        Bitmap bitmap = null;        if (mMaxWidth == 0 && mMaxHeight == 0) {            decodeOptions.inPreferredConfig = mDecodeConfig;            //原来是解析网络请求返回的字节数组//            bitmap = BitmapFactory.decodeByteArray(data, 0, data.length, decodeOptions);            bitmap = BitmapFactory.decodeFile(url, decodeOptions);        } else {            // If we have to resize this image, first get the natural bounds.            decodeOptions.inJustDecodeBounds = true;            BitmapFactory.decodeFile(url, decodeOptions);            int actualWidth = decodeOptions.outWidth;            int actualHeight = decodeOptions.outHeight;            // Then compute the dimensions we would ideally like to decode to.            int desiredWidth = getResizedDimension(mMaxWidth, mMaxHeight,                    actualWidth, actualHeight, mScaleType);            int desiredHeight = getResizedDimension(mMaxHeight, mMaxWidth,                    actualHeight, actualWidth, mScaleType);            // Decode to the nearest power of two scaling factor.            decodeOptions.inJustDecodeBounds = false;            // TODO(ficus): Do we need this or is it okay since API 8 doesn't support it?            // decodeOptions.inPreferQualityOverSpeed = PREFER_QUALITY_OVER_SPEED;            decodeOptions.inSampleSize =                    findBestSampleSize(actualWidth, actualHeight, desiredWidth, desiredHeight);//            Bitmap tempBitmap =//                    BitmapFactory.decodeByteArray(data, 0, data.length, decodeOptions);            Bitmap tempBitmap =                    BitmapFactory.decodeFile(url, decodeOptions);            // If necessary, scale down to the maximal acceptable size.            if (tempBitmap != null && (tempBitmap.getWidth() > desiredWidth ||                    tempBitmap.getHeight() > desiredHeight)) {                bitmap = Bitmap.createScaledBitmap(tempBitmap,                        desiredWidth, desiredHeight, true);                tempBitmap.recycle();            } else {                bitmap = tempBitmap;            }        }        return bitmap;    }    /**     * 获取期望的width和heigth     *     * @param maxPrimary     * @param maxSecondary     * @param actualPrimary     * @param actualSecondary     * @param scaleType     * @return     */    private static int getResizedDimension(int maxPrimary, int maxSecondary, int actualPrimary,                                           int actualSecondary, ImageView.ScaleType scaleType) {        // If no dominant value at all, just return the actual.        if ((maxPrimary == 0) && (maxSecondary == 0)) {            return actualPrimary;        }        // If ScaleType.FIT_XY fill the whole rectangle, ignore ratio.        if (scaleType == ImageView.ScaleType.FIT_XY) {            if (maxPrimary == 0) {                return actualPrimary;            }            return maxPrimary;        }        // If primary is unspecified, scale primary to match secondary's scaling ratio.        if (maxPrimary == 0) {            double ratio = (double) maxSecondary / (double) actualSecondary;            return (int) (actualPrimary * ratio);        }        if (maxSecondary == 0) {            return maxPrimary;        }        double ratio = (double) actualSecondary / (double) actualPrimary;        int resized = maxPrimary;        // If ScaleType.CENTER_CROP fill the whole rectangle, preserve aspect ratio.        if (scaleType == ImageView.ScaleType.CENTER_CROP) {            if ((resized * ratio) < maxSecondary) {                resized = (int) (maxSecondary / ratio);            }            return resized;        }        if ((resized * ratio) > maxSecondary) {            resized = (int) (maxSecondary / ratio);        }        return resized;    }    /**     * 计算缩放比例     *     * @param actualWidth     * @param actualHeight     * @param desiredWidth     * @param desiredHeight     * @return     */    static int findBestSampleSize(            int actualWidth, int actualHeight, int desiredWidth, int desiredHeight) {        double wr = (double) actualWidth / desiredWidth;        double hr = (double) actualHeight / desiredHeight;        double ratio = Math.min(wr, hr);        float n = 1.0f;        while ((n * 2) <= ratio) {            n *= 2;        }        return (int) n;    }}

我写的这个imageloader的图片解析代码基本是借用volley的ImageRequest中的代码，两者的区别在于一个是用于加载本地图片，一个加载网络图片。

文中我提到两点：

Universal-Image-Loader,和gridview结合不好用，常不能显示本地图片
volley的图片加载也不适用与本地图片

不知大家是否认同我的这两点，如果不认同，还请指正

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