<LinearLayout 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"

  android:orientation="vertical" >



  <ImageView

    android:id="@+id/imageview"

    android:layout_width="wrap_content"

    android:layout_height="wrap_content" />

  

   <Button

    android:id="@+id/bt_download"

    android:layout_width="wrap_content"

    android:layout_height="wrap_content"

    android:text="圖片下載"

    android:onClick="Image_Download" />



</LinearLayout>

//操作SDCARD的文件工具類

public class FileUtil {



 private static final String CACHE_DIR = Environment.getExternalStorageDirectory() + "/my_caches/images";



 private static int COMP_JPG = 0;

 private static int COMP_PNG = 1;

//判斷sdcard 是否掛載(是否有sdcard)

 public static boolean isMounted(){

 String state = Environment.getExternalStorageState();

 return state.equals(Environment.MEDIA_MOUNTED);

 }



 //獲取sdcard文件 根路徑的絕對路徑

 public static String getSDCARD(){

 return Environment.getExternalStorageDirectory().getAbsolutePath();

 }



 //獲取文件名 

 public static String getFilename(String url){

 return url.substring(url.lastIndexOf('/') + 1);

 }



 //保存文件 方法1

 

 public static void sava1(String url,byte[] data){

 //判斷是否有sdcard

 if(!isMounted()){

 return ; 

 }

 //有sdcard

 //判斷是否有緩存文件夾

 File dir = new File(CACHE_DIR);

 if(!dir.exists()){

 //不存在緩存文件夾 創(chuàng)建文件夾用來保存文件

 dir.mkdirs();

 }

 //把文件 數(shù)據(jù)存到sdcard

 File file = new File(dir,getFilename(url));

 try {

 FileOutputStream fos = new FileOutputStream(file);

 fos.write(data);

 

 fos.close();

 } catch (Exception e) {

 e.printStackTrace();

 }

 }

 

 //保存文件 方法2

 public static void sava2(String url,Bitmap bitmap,int format){

 //判斷 是否有sdcard

 if(!isMounted()){

 return ;

 }

 File dir = new File(CACHE_DIR);

 if(!dir.exists()){

 dir.mkdirs();

 }

 //把 文件數(shù)據(jù) 寫到 sdcard

 File file = new File(dir,getFilename(url));

 try {

 FileOutputStream fos = new FileOutputStream(file);

 //把圖片文件寫入緩存

 bitmap.compress((format == COMP_JPG?CompressFormat.JPEG:CompressFormat.PNG), 100, fos);

 

 fos.close();

 } catch (Exception e) {

 e.printStackTrace();

 }

 

 }

 //讀取圖片

 public static Bitmap readImage(String url){

 if(!isMounted()){

 return null;

 }

 File file = new File(CACHE_DIR,getFilename(url));

 if(file.exists()){

 return BitmapFactory.decodeFile(file.getAbsolutePath());

 }

 return null;

 }

 

 //清空 緩存目錄

 public void clearCaches(){

 File dir = new File(CACHE_DIR);

 File[] file_datas = dir.listFiles();

 for(File file : file_datas){

 file.delete();

 }

 }

 

}

public class MainActivity extends Activity {



 private ImageView imageview;

 

 private String url = "http://b.hiphotos.baidu.com/image/pic/item/d1160924ab18972bf5f68cc8e0cd7b899f510ae7.jpg";

 @Override

 protected void onCreate(Bundle savedInstanceState) {

 super.onCreate(savedInstanceState);

 setContentView(R.layout.activity_main);

 

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

 //設置默認圖片

 imageview.setImageResource(R.drawable.ic_launcher);

 

 }

 //圖片下載 按鈕 點擊事件 監(jiān)聽

 public void Image_Download(View view){

 //判斷本地是否有圖片

 Bitmap bitmap = FileUtil.readImage(url);

 if(bitmap != null){

 imageview.setImageBitmap(bitmap);

 }else{

 //沒有圖片 就發(fā)送聯(lián)網請求

 new MyAsyncTask().execute(url);

 }

 }

 

 //聯(lián)網工具類

 public class MyAsyncTask extends AsyncTask<String, Void, byte[]>{



 @Override

 protected byte[] doInBackground(String... params) {

 

 HttpGet get = new HttpGet(params[0]);

 HttpClient client = new DefaultHttpClient();

 HttpResponse response;

 try {

 response = client.execute(get);

 if(response.getStatusLine().getStatusCode() == 200){

 byte[] data = EntityUtils.toByteArray(response.getEntity());

 FileUtil.sava1(params[0], data);

 return data;

 }

 }

 catch (Exception e) {

 e.printStackTrace();

 }

 return null;

 }

 @Override

 protected void onPostExecute(byte[] result) {

 super.onPostExecute(result);

 if(result != null){

 Bitmap bitmap = BitmapFactory.decodeByteArray(result, 0, result.length);

 imageview.setImageBitmap(bitmap);

 }

 }

 

 }

}