Bitmap高效的加载图片

• 为什么要高效加载
  • 由于Bitmap的特殊性以及android对单个应用所施加的内存限制，比如16MB，这就导致加载Bitmap的时候很容易出现内存溢出
• 高效加载四个步骤
  • options true
  • 获取outHeight outWidh
  • 计算采样率
  • 加载图片

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

/**
 * MyApplication
 * Created by lzw on 2019/2/28. 15:09:25
 * 邮箱：632393724@qq.com
 * All Rights Saved! Chongqing AnYun Tech co. LTD
 */
public class BitmapUtil {
//如何加载一个Bitmap  四种方法 BitmapFactory  decodeResource  decodeStream decodefile decodeByteArray
    public static Bitmap decodeSampledBitmapFromResource(Resources resources,int resId,
                                                         int reqWidth,int reqHeight){
        BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;//BitmapFactory 只会解析原始图片的宽、高信息，并不会真正地加载图片
         BitmapFactory.decodeResource(resources,resId,options);
         options.inSampleSize = calculateInSampleSize(options,reqWidth,reqHeight);// 2 3步合到一起了
         options.inJustDecodeBounds = false;//设置成false才会加载图片 ，切记~~
        return      BitmapFactory.decodeResource(resources,resId,options);
    }

    private static int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) {
        final  int height = options.outHeight;
        final int width = options.outWidth;
        Log.i("BitmapUtil", "calculateInSampleSize: outHeight"+height+" width="+width);
        int sampleSize = 1;

        if (height > reqHeight || width>reqWidth){
            final int halfWidth = width/2;
            final int halfHeight = height/2;
            while ((halfHeight/sampleSize)>=reqHeight && (halfWidth/sampleSize)>=reqWidth){
                sampleSize*=2;
            }
        }
        Log.i("BitmapUtil", "calculateInSampleSize: ="+sampleSize);
        return sampleSize;
    }
}

　　

  Bitmap bitmap = BitmapUtil.decodeSampledBitmapFromResource(getResources(),R.drawable.abc,100,100);
        int count=bitmap.getAllocationByteCount();
        Log.i(TAG, "initView: count="+count);
        imageView.setImageBitmap(bitmap);