<?xml version="1.0" encoding="utf-8"?>

 <RelativeLayout

     xmlns:android="http://schemas.android.com/apk/res/android"

     xmlns:tools="http://schemas.android.com/tools"

     android:layout_width="match_parent"

     android:layout_height="match_parent"

     tools:context=".MainActivity">

     <ImageView

         android:id="@+id/img"

         android:layout_width="200dp"

         android:layout_height="200dp"

         android:layout_centerHorizontal="true"

         android:layout_marginTop="50dp"

         android:background="#aa111222"

         android:onClick="getPicture"

         />

 </RelativeLayout>

 package com.example.administrator.getpicture;

 import android.app.Activity;

 import android.content.ContentResolver;

 import android.content.Intent;

 import android.graphics.Bitmap;

 import android.graphics.BitmapFactory;

 import android.net.Uri;

 import android.os.Bundle;

 import android.provider.MediaStore;

 import android.util.Log;

 import android.view.View;

 import android.widget.ImageView;

 import java.io.InputStream;

 public class MainActivity extends Activity {

     private ImageView img;

     @Override

     protected void onCreate(Bundle savedInstanceState) {

         super.onCreate(savedInstanceState);

         setContentView(R.layout.activity_main);

         img = (ImageView)this.findViewById(R.id.img);

     }

     //图片点击事件

     public void getPicture(View v)

     {

         Intent intent = new Intent(Intent.ACTION_PICK,null);

         intent.setDataAndType(MediaStore.Images.Media.EXTERNAL_CONTENT_URI,"image/*");

         //intent 待启动的Intent 100（requestCode）请求码，返回时用来区分是那次请求

         startActivityForResult(intent ,100);

     }

     @Override

     protected void onActivityResult(int requestCode, int resultCode, Intent data) {

         //返回成功，请求码（对应启动时的requestCode）

         if(resultCode == RESULT_OK && requestCode==100)

         {

             //方式一（不建议使用）

             //下面的一句代码，也可以把图片显示在ImageView中

             //但图片过大的时候，将无法显示，所以

             //img.setImageURI(data.getData());

             //方式二

             Uri uri = data.getData();

             ContentResolver cr = this.getContentResolver();

             try {

                 //根据Uri获取流文件

                 InputStream is = cr.openInputStream(uri);

                 BitmapFactory.Options options = new BitmapFactory.Options();

                 options.inSampleSize =3;

                 Bitmap bitmap = BitmapFactory.decodeStream(is,null,options);

                 img.setImageBitmap(bitmap);

             }

             catch(Exception e)

             {

                 Log.i("lyf", e.toString());

             }

         }

         super.onActivityResult(requestCode, resultCode, data);

     }

 }