SharedPreferences详解(三)——存取图片

MainActivity如下:

 package cc.sp;

 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
 import android.os.Bundle;
 import android.util.Base64;
 import android.view.View;
 import android.view.View.OnClickListener;
 import android.widget.Button;
 import android.widget.ImageView;
 import android.app.Activity;
 import android.content.Context;
 import android.content.SharedPreferences;
 import android.content.SharedPreferences.Editor;
 import android.graphics.Bitmap;
 import android.graphics.Bitmap.CompressFormat;
 import android.graphics.BitmapFactory;
 /**
  * Demo描述:
  * 利用SharedPreferences存取图片
  *
  *
  * 参考资料:
  * 1 http://blog.csdn.net/tangnengwu/article/details/37881087
  * 2 http://blog.csdn.net/lfdfhl/article/details/37742775
  * 3 http://blog.csdn.net/lfdfhl/article/details/17998469
  * 4 http://blog.csdn.net/lfdfhl/article/details/10961459
  *   Thank you very much
  *
  */
 public class MainActivity extends Activity {
     private Button mSaveButton;
     private Button mGetButton;
     private ImageView mImageView;
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.main);
         init();
     }

     private void init(){
         mSaveButton=(Button) findViewById(R.id.saveButton);
         mSaveButton.setOnClickListener(new OnClickListener() {
             @Override
             public void onClick(View view) {
                 saveBitmapToSharedPreferences();
             }
         });
         mGetButton=(Button) findViewById(R.id.getButton);
         mGetButton.setOnClickListener(new OnClickListener() {
             @Override
             public void onClick(View view) {
                 getBitmapFromSharedPreferences();
             }
         });
         mImageView=(ImageView) findViewById(R.id.imageView);
     }

     /**
      * 将Bitmap转换成字符串保存至SharedPreferences
      *
      * 注意:
      * 在压缩图片至输出流时,不要选择CompressFormat.JPEG而该是PNG,否则会造成图片有黑色背景.
      * 详见参考资料二
      */
     private void saveBitmapToSharedPreferences(){
         Bitmap bitmap=BitmapFactory.decodeResource(getResources(), R.drawable.ic_launcher);
         //第一步:将Bitmap压缩至字节数组输出流ByteArrayOutputStream
         ByteArrayOutputStream byteArrayOutputStream=new ByteArrayOutputStream();
         bitmap.compress(CompressFormat.PNG, 80, byteArrayOutputStream);
         //第二步:利用Base64将字节数组输出流中的数据转换成字符串String
         byte[] byteArray=byteArrayOutputStream.toByteArray();
         String imageString=new String(Base64.encodeToString(byteArray, Base64.DEFAULT));
         //第三步:将String保持至SharedPreferences
         SharedPreferences sharedPreferences=getSharedPreferences("testSP", Context.MODE_PRIVATE);
         Editor editor=sharedPreferences.edit();
         editor.putString("image", imageString);
         editor.commit();
     }

     /**
      * 从SharedPreferences中取出Bitmap
      */
     private void getBitmapFromSharedPreferences(){
         SharedPreferences sharedPreferences=getSharedPreferences("testSP", Context.MODE_PRIVATE);
         //第一步:取出字符串形式的Bitmap
         String imageString=sharedPreferences.getString("image", "");
         //第二步:利用Base64将字符串转换为ByteArrayInputStream
         byte[] byteArray=Base64.decode(imageString, Base64.DEFAULT);
         ByteArrayInputStream byteArrayInputStream=new ByteArrayInputStream(byteArray);
         //第三步:利用ByteArrayInputStream生成Bitmap
         Bitmap bitmap=BitmapFactory.decodeStream(byteArrayInputStream);
         mImageView.setImageBitmap(bitmap);
     }

 }

activity_main.xml如下:

 <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"
    >

     <Button
         android:id="@+id/saveButton"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:text="保存图片到SharedPreferences"
         android:layout_centerHorizontal="true"
         android:layout_marginTop="25dip"/>

      <Button
         android:id="@+id/getButton"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:text="从SharedPreferences获取图片"
         android:layout_centerHorizontal="true"
         android:layout_marginTop="80dip"/>

      <ImageView
         android:id="@+id/imageView"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:layout_centerInParent="true"
         />

 </RelativeLayout>