本文实例介绍了sdcard存储图片下载简单操作，分享给大家供大家参考，具体内容如下

步骤 -- 在配置清单添加完联网权限后

1、res/layout界面布局

<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="图片下载"

    android:onClick="Image_Download" />



</LinearLayout>

2、有2个类一个操作SDCARD的文件工具类(FileUtil)另外一个MainActivity类

FileUtil类

//操作SDCARD的文件工具类

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;

//判断sdcard 是否挂载(是否有sdcard)

 public static boolean isMounted(){

 String state = Environment.getExternalStorageState();

 return state.equals(Environment.MEDIA_MOUNTED);

 }



 //获取sdcard文件 根路径的绝对路径

 public static String getSDCARD(){

 return Environment.getExternalStorageDirectory().getAbsolutePath();

 }



 //获取文件名 

 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){

 //判断是否有sdcard

 if(!isMounted()){

 return ; 

 }

 //有sdcard

 //判断是否有缓存文件夹

 File dir = new File(CACHE_DIR);

 if(!dir.exists()){

 //不存在缓存文件夹 创建文件夹用来保存文件

 dir.mkdirs();

 }

 //把文件 数据存到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){

 //判断 是否有sdcard

 if(!isMounted()){

 return ;

 }

 File dir = new File(CACHE_DIR);

 if(!dir.exists()){

 dir.mkdirs();

 }

 //把 文件数据 写到 sdcard

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

 try {

 FileOutputStream fos = new FileOutputStream(file);

 //把图片文件写入缓存

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

 

 fos.close();

 } catch (Exception e) {

 e.printStackTrace();

 }

 

 }

 //读取图片

 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 缓存目录

 public void clearCaches(){

 File dir = new File(CACHE_DIR);

 File[] file_datas = dir.listFiles();

 for(File file : file_datas){

 file.delete();

 }

 }

 

}

MainActivity类

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);

 //设置默认图片

 imageview.setImageResource(R.drawable.ic_launcher);

 

 }

 //图片下载 按钮 点击事件 监听

 public void Image_Download(View view){

 //判断本地是否有图片

 Bitmap bitmap = FileUtil.readImage(url);

 if(bitmap != null){

 imageview.setImageBitmap(bitmap);

 }else{

 //没有图片 就发送联网请求

 new MyAsyncTask().execute(url);

 }

 }

 

 //联网工具类

 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);

 }

 }

 

 }

}

以上就是本文的全部内容，希望对大家学习Android软件编程有所帮助。