Android之等比例显示图片

　　在android中，由于密度的影响，如果想得到图片的宽高是不行的，具体为什么我就大概说一下，具体的请搜索度娘或者古哥吧。 原因是如果你把图片放在drawable-mdpi里，而手机是属于drawable-hdpi的话，图片是被自动放大，就这样取到的宽与高未必就是正确的。那么如何让android上面显示的图片是基于原来图片的比例呢，首先你可以在res目录下创建一个drawable-nodpi的目录，这个目录下的图片是不根据dpi的多少来进行拉伸或者缩小滴。然后，就是根据屏幕的宽 和 图片的宽高 得出图片在屏幕显示的高，宽是固定的，就是屏幕的宽，所以不用算了。

private void getWidth_Height() {
        Display display = getWindowManager().getDefaultDisplay();
        int width = display.getWidth(); // deprecated
        int height = display.getHeight(); // deprecated

        Bitmap mBitmap = createImageWithResouce(R.drawable.history4);
        image.setLayoutParams(new LayoutParams(width, width / getBitmapWidth(mBitmap) * getBitmapHeight(mBitmap)));
        image.setImageBitmap(createImageWithResouce(R.drawable.history4));
    }

    private Bitmap createImageWithResouce(int resourceID) {
        Bitmap bit = BitmapFactory.decodeResource(getResources(), R.drawable.history4);
        return bit;
    }

    private int getBitmapWidth(Bitmap bitmap){
        return bitmap.getWidth();
    }
    private int getBitmapHeight(Bitmap bitmap){
        return bitmap.getHeight();
    }

    // 释放bitmap
    private void releaseBitmap(Bitmap bitmap){
        if (bitmap!=null && !bitmap.isRecycled()) {
            bitmap.recycle();
            bitmap = null;
        }
    }

建议使用如下的这种，应用了LruCache作为管理

public class ImageUtil {
    private LruCache<String, Bitmap> mMemoryCache;
    private final Context mContext;

    private static ImageUtil imageUtil;

    private static Object obj = new Object();

    private int memClass;

    private int cacheSize;

    private ImageUtil(Context mContext) {
        this.mContext = mContext;
        createLruCache(mContext);
    }

    private void createLruCache(Context mContext) {
        memClass = ((ActivityManager) mContext.getSystemService(Context.ACTIVITY_SERVICE)).getMemoryClass();
        cacheSize = 1024 * 1024 * memClass / 8;
        mMemoryCache = new LruCache<String, Bitmap>(cacheSize) {
            @Override
            protected int sizeOf(String key, Bitmap value) {
                // TODO Auto-generated method stub
                return value.getRowBytes();
            }

        };
    }

    public static ImageUtil getInstance(Context mContext) {
        if (imageUtil == null) {
            synchronized (obj) {
                if (imageUtil == null) {
                    imageUtil = new ImageUtil(mContext);
                }
            }
        }
        return imageUtil;
    }

    public void adjustImageSize(ImageView imageView, int imageResourceId) {
        Bitmap mBitmap = null;
        Display display = ((MainActivity) mContext).getWindowManager().getDefaultDisplay();
        int width = display.getWidth(); // deprecated
        int height = display.getHeight(); // deprecated

        Bitmap bitmapCache = mMemoryCache.get(imageResourceId + "");
        if (bitmapCache != null) {
            mBitmap = bitmapCache;
        } else {
            mBitmap = createImageWithResouce(mContext, imageResourceId);
            mMemoryCache.put(imageResourceId + "", mBitmap);
        }

        RelativeLayout.LayoutParams layoutParams = new RelativeLayout.LayoutParams(width, width
                / getBitmapWidth(mBitmap) * getBitmapHeight(mBitmap));
        layoutParams.addRule(RelativeLayout.ALIGN_PARENT_BOTTOM);

        imageView.setLayoutParams(layoutParams);

        imageView.setBackgroundDrawable(new BitmapDrawable(mBitmap));
        // imageView.setImageBitmap(mBitmap);
    }

    private static Bitmap createImageWithResouce(Context context, int resourceID) {
        Bitmap bit = BitmapFactory.decodeResource(context.getResources(), R.drawable.ic_launcher);
        return bit;
    }

    private int getBitmapWidth(Bitmap bitmap) {
        return bitmap.getWidth();
    }

    private int getBitmapHeight(Bitmap bitmap) {
        return bitmap.getHeight();
    }
}