也是直接上代码吧

 1 package cn.itcast.resizeimage;
 2 
 3 import java.io.FileNotFoundException;
 4 import java.io.IOException;
 5 import java.io.InputStream;
 6 
 7 import android.app.Activity;
 8 import android.content.Intent;
 9 import android.graphics.Bitmap;
10 import android.graphics.BitmapFactory;
11 import android.graphics.BitmapFactory.Options;
12 import android.net.Uri;
13 import android.os.Bundle;
14 import android.view.Display;
15 import android.view.View;
16 import android.view.WindowManager;
17 import android.widget.ImageView;
18 
19 public class LoadImageActivity extends Activity {
20   private ImageView iv;
21   private WindowManager wm;
22   private Display  display;
23     @Override
24   public void onCreate(Bundle savedInstanceState) {
25 super.onCreate(savedInstanceState);
26         setContentView(R.layout.main);
27         iv = (ImageView) findViewById(R.id.iv);
28         wm = getWindowManager();
29 //获取手机的屏幕宽高30         display = wm.getDefaultDisplay();
31     }
32 
33   public void selectImage(View view) {
34         Intent intent = new Intent();
35         intent.setAction("android.intent.action.PICK");
36         intent.addCategory("android.intent.category.DEFAULT");
37         intent.setType("image/*");
38         startActivityForResult(intent, 0);
39 
40     }
41 
42     @Override
43   protected void onActivityResult(int requestCode, int resultCode, Intent data) {
44 try {
45  if (data != null) {
46   // 得到点击图片的uri47                 Uri uri = data.getData();
48   //对 要加载的图片进行缩放
49   //1.得到图片的宽度和高度.
50   //由于我们只想得到图片的宽度和高度,这个时候 只需要解析图片的头信息51                 BitmapFactory.Options opts = new Options();
52                 opts.inJustDecodeBounds = true;//让 bimapfactory假的解析这个位图,只获取位图的边框信息53                 InputStream is = getContentResolver().openInputStream(uri);
54                 BitmapFactory.decodeStream(is);
55                 
56   int bitmapHeight =     opts.outHeight;
57   int bitmapWidth = opts.outWidth;
58                 
59   int windowHeight = display.getHeight();
60   int windowWidth = display.getWidth();
61   //获取水平和垂直方向的缩放比62   int scaley = bitmapHeight / windowHeight;
63   int scalex = bitmapWidth / windowWidth;
64   if(scalex>scaley&&scaley>1){
65                     opts.inSampleSize = scalex;
66                 }
67   if(scaley>scalex&&scalex>1){
68                     opts.inSampleSize = scaley;
69                 }
70                 opts.inJustDecodeBounds = false;// 由于已经得到了缩放比例 ,让位图工厂真正的解析这个位图
71   // 由于前面 我们已经解析了这个输入流, 需要重新初始化这个输入流72                 is = getContentResolver().openInputStream(uri);
73                 Bitmap bitmap =  BitmapFactory.decodeStream(is);
74                 
75                 
76                 
77                 iv.setImageBitmap(bitmap);
78             }
79         } catch (Exception e) {
80             e.printStackTrace();
81         }
82 super.onActivityResult(requestCode, resultCode, data);
83     }
84 }

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