图片有各种形状和大小。在很多情况下这些图片是远远大于我们的用户界面(UI)且占领着极大的内存空间，假设我们不正确位图进行压缩处理，我们的程序会发生内存泄露的错误。

MainActivity的代码

package com.example.g08_bitmap;import android.os.Bundle;
import android.app.Activity;
import android.content.res.Resources;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.widget.ImageView;public class MainActivity extends Activity {private ImageView imageView;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);imageView = (ImageView) this.findViewById(R.id.imageView1);imageView.setImageBitmap(decodeSampledBitmapFromResource(getResources(), R.drawable.a, 300, 300));}public static Bitmap decodeSampledBitmapFromResource(Resources res,int resId, int reqWidth, int reqHeight) {final BitmapFactory.Options options = new BitmapFactory.Options();//先将inJustDecodeBounds属性设置为true,解码避免内存分配options.inJustDecodeBounds = true;// 将图片传入选择器中BitmapFactory.decodeResource(res, resId, options);// 对图片进行指定比例的压缩options.inSampleSize = calculateInSampleSize(options, reqWidth,reqHeight);//待图片处理完毕后再进行内存的分配，避免内存泄露的发生options.inJustDecodeBounds = false;return BitmapFactory.decodeResource(res, resId, options);}// 计算图片的压缩比例public static int calculateInSampleSize(BitmapFactory.Options options,int reqWidth, int reqHeight) {// Raw height and width of imagefinal int height = options.outHeight;final int width = options.outWidth;int inSampleSize = 1;if (height > reqHeight || width > reqWidth) {final int heightRatio = Math.round((float) height/ (float) reqHeight);final int widthRatio = Math.round((float) width / (float) reqWidth);// 选择长宽高较小的比例，成为压缩比例inSampleSize = heightRatio < widthRatio ? heightRatio : widthRatio;}return inSampleSize;}}