Android 把从网络获取的图片缓存到内存中

1：activity_main.xml

<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/btn_1"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:text="Button test1"/>



    <Button 

        android:layout_below="@id/btn_1"

        android:id="@+id/btn_2"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:text="Button Intent Other Activity"/>

    

    <ImageView 

        android:layout_below="@id/btn_2"

        android:id="@+id/img_view"

        android:layout_width="match_parent"

        android:layout_height="match_parent"/>



</RelativeLayout>

2:HttpHelper.java

public class HttpHelper {

    //图片资源缓存

    private static Map<String,Bitmap>bitmapCache=new HashMap<String,Bitmap>();

    

    public static Bitmap getHttpBitmap(String url){
　　　　　//首先先从缓存中取数据

        Bitmap bitmap=bitmapCache.get(url);

        if(bitmap!=null){
　　　　　　　　//如果取到就直接返回

            return bitmap;

        }

        

        try{

            URL myUrl=new URL(url);

            HttpURLConnection conn=(HttpURLConnection)myUrl.openConnection();

            conn.setDoInput(true);

            conn.connect();

            InputStream is=conn.getInputStream();

            bitmap=BitmapFactory.decodeStream(is);

            is.close();

        }catch(Exception e){

            e.printStackTrace();

        }

        

        if(bitmap!=null){
　　　　　　　　//将获取到的图片缓存起来

            bitmapCache.put(url, bitmap);

        }

        

        return bitmap;

    }

}

3：MainActivity.java

public class MainActivity extends Activity {

    private Button btnTest1=null;

    private Button btnTest2=null;

    private ImageView imgView=null;

    private Bitmap bitmap=null;

    

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        

        initUI();

        

        btnTest1.setOnClickListener(new OnClickListener(){

            public void onClick(View view){

                new Thread(new GetImgThread()).start();

            }

        });

        

        btnTest2.setOnClickListener(new OnClickListener(){

            public void onClick(View view){

                Intent intent=new Intent(MainActivity.this,OtherActivity.class);

                startActivity(intent);

            }

        });

    }



    private void initUI(){

        btnTest1=(Button)findViewById(R.id.btn_1);

        btnTest2=(Button)findViewById(R.id.btn_2);

        imgView=(ImageView)findViewById(R.id.img_view);

    }



    Handler myHandler=new Handler(){

        public void handleMessage(Message msg){

            imgView.setImageBitmap(bitmap);

        }

    };

    

    class GetImgThread implements Runnable{

        public void run(){

            String url="http://upload.wikimedia.org/wikipedia/commons/thumb/e/ea/Hukou_Waterfall.jpg/800px-Hukou_Waterfall.jpg";

            bitmap=HttpHelper.getHttpBitmap(url);

            myHandler.obtainMessage().sendToTarget();

        }

    }

}

4:activity_other.xml

<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/btn_get"

         android:layout_width="match_parent"

         android:layout_height="wrap_content"

         android:text="Button Get Img"/>

     

    <ImageView 

        android:id="@+id/img_view_2"

        android:layout_below="@id/btn_get"

        android:layout_width="match_parent"

        android:layout_height="match_parent"/>

</RelativeLayout>

5:OtherActivity.java

public class OtherActivity extends Activity {

    private  Bitmap bitmap=null;

    private Button btnGetImg=null;

    private ImageView imgView=null;

    

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_other);

        

        btnGetImg=(Button)findViewById(R.id.btn_get);

        imgView=(ImageView)findViewById(R.id.img_view_2);

        

        btnGetImg.setOnClickListener(new OnClickListener(){

            public void onClick(View view){

                new Thread(new GetImgThread()).start();

            }

        });

    }

    

    Handler myHandler=new Handler(){

        public void handleMessage(Message msg){

            imgView.setImageBitmap(bitmap);

        }

    };

    

    class GetImgThread implements Runnable{

        public void run(){

            String url="http://upload.wikimedia.org/wikipedia/commons/thumb/e/ea/Hukou_Waterfall.jpg/800px-Hukou_Waterfall.jpg";

            bitmap=HttpHelper.getHttpBitmap(url);

            myHandler.obtainMessage().sendToTarget();

        }

    }



}

6:运行结果如下：