图片有各种形状和大小。在许多情况下这些图片是远远大于我们的用户界面(UI)且占据着极大的内存空间，如果我们不对位图进行压缩处理，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; @Override protected 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); //待图片处理完成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 image final 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; }}