BitmapDecoder.java

/**
 * Copyright (c) 2012-2013, Michael Yang 杨福海 (www.yangfuhai.com).
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package cn.coderss.bitmap;

import android.content.res.Resources;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.util.Log;

import java.io.FileDescriptor;

public class BitmapDecoder {
	private static final String TAG = "BitmapDecoder";
	private BitmapDecoder(){}

    public static Bitmap decodeSampledBitmapFromResource(Resources res, int resId,int reqWidth, int reqHeight) {

        final BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;
        options.inPurgeable = true;
        BitmapFactory.decodeResource(res, resId, options);
        options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
        options.inJustDecodeBounds = false;
        try {
        	  return BitmapFactory.decodeResource(res, resId, options);
		} catch (OutOfMemoryError e) {
			 Log.e(TAG, "decodeSampledBitmapFromResource内存溢出，如果频繁出现这个情况 可以尝试配置增加内存缓存大小");
			 e.printStackTrace();
			 return null;
		}
    }

    public static Bitmap decodeSampledBitmapFromFile(String filename,int reqWidth, int reqHeight) {
        final BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;
        options.inPurgeable = true;
        BitmapFactory.decodeFile(filename, options);
        options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
        options.inJustDecodeBounds = false;
        try {
        	  return BitmapFactory.decodeFile(filename, options);
		} catch (OutOfMemoryError e) {
			 Log.e(TAG, "decodeSampledBitmapFromFile内存溢出，如果频繁出现这个情况 可以尝试配置增加内存缓存大小");
			 e.printStackTrace();
			 return null;
		}
    }

    public static Bitmap decodeSampledBitmapFromDescriptor(FileDescriptor fileDescriptor, int reqWidth, int reqHeight) {

        final BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;
        options.inPurgeable = true;
        BitmapFactory.decodeFileDescriptor(fileDescriptor, null, options);
        options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
        options.inJustDecodeBounds = false;
        try {
        	 return BitmapFactory.decodeFileDescriptor(fileDescriptor, null, options);
		} catch (OutOfMemoryError e) {
			 Log.e(TAG, "decodeSampledBitmapFromDescriptor内存溢出，如果频繁出现这个情况 可以尝试配置增加内存缓存大小");
			 e.printStackTrace();
			 return null;
		}
    }

    public static int calculateInSampleSize(BitmapFactory.Options options,int reqWidth, int reqHeight) {
        final int height = options.outHeight;
        final int width = options.outWidth;
        int inSampleSize = 1;

        if (height > reqHeight || width > reqWidth) {
            if (width > height) {
                inSampleSize = Math.round((float) height / (float) reqHeight);
            } else {
                inSampleSize = Math.round((float) width / (float) reqWidth);
            }

            final float totalPixels = width * height;

            final float totalReqPixelsCap = reqWidth * reqHeight * 2;

            while (totalPixels / (inSampleSize * inSampleSize) > totalReqPixelsCap) {
                inSampleSize++;
            }
        }
        return inSampleSize;
    }
}