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：

Android 把从网络获取的图片缓存到内存中

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