android - 如何在 Android 的 imageview 中下载和查看图像？

Question

我正在尝试显示来自我的服务器的两个图像。我怎么能做到这一点？

Android 中是否有任何选项可用于从服务器为每个实例动态更改图像？

我正在使用权限作为，。

 <uses-permission android:name="android.permission.INTERNET" />

Answer 1

试试这个例子。它将帮助您从在线获取图像

Xml 文件是

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >

<TextView
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:layout_margin="10dip"
    android:text="Loading image from url" />

<Button
    android:id="@+id/button1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Button" />

<ImageView
    android:id="@+id/image"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_margin="10dip" />

<ImageView
    android:id="@+id/image1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_margin="10dip" />

<ImageView
    android:id="@+id/image2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_margin="10dip" />

<ImageView
    android:id="@+id/image3"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_margin="10dip" />
 </LinearLayout>

而java文件是，..

public class AndroidLoadImageFromURLActivity extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    // Loader image - will be shown before loading image
    final int loader = R.drawable.loader;

    // Imageview to show
    final ImageView image = (ImageView) findViewById(R.id.image);
    final ImageView image1 = (ImageView) findViewById(R.id.image1);
    final ImageView image2 = (ImageView) findViewById(R.id.image2);
    final ImageView image3 = (ImageView) findViewById(R.id.image3);
    Button b=(Button)findViewById(R.id.button1);


    // Image url
    final String image_url = "URL";
    final String image_url2 = "URL";
    final String image_url3 = "URL";
    final String image_url4 = "URL";

    // ImageLoader class instance
    final ImageLoader imgLoader = new ImageLoader(getApplicationContext());

    // whenever you want to load an image from url
    // call DisplayImage function
    // url - image url to load
    // loader - loader image, will be displayed before getting image
    // image - ImageView 
    b.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub


    imgLoader.DisplayImage(image_url, loader, image);
    imgLoader.DisplayImage(image_url4, loader, image3);
    imgLoader.DisplayImage(image_url2, loader, image1);
    imgLoader.DisplayImage(image_url3, loader, image2);
        }
    });
}
}

public class FileCache {

private File cacheDir;

public FileCache(Context context){
    //Find the dir to save cached images
    if (android.os.Environment.getExternalStorageState().equals(android.os.Environment.MEDIA_MOUNTED))
        cacheDir=new File(android.os.Environment.getExternalStorageDirectory(),"TempImages");
    else
        cacheDir=context.getCacheDir();
    if(!cacheDir.exists())
        cacheDir.mkdirs();
}

public File getFile(String url){
    String filename=String.valueOf(url.hashCode());
    File f = new File(cacheDir, filename);
    return f;

}

public void clear(){
    File[] files=cacheDir.listFiles();
    if(files==null)
        return;
    for(File f:files)
        f.delete();
}

}

public class ImageLoader {

MemoryCache memoryCache=new MemoryCache();
FileCache fileCache;
private Map<ImageView, String> imageViews=Collections.synchronizedMap(new WeakHashMap<ImageView, String>());
ExecutorService executorService; 

public ImageLoader(Context context){
    fileCache=new FileCache(context);
    executorService=Executors.newFixedThreadPool(5);
}

int stub_id = R.drawable.ic_launcher;
public void DisplayImage(String url, int loader, ImageView imageView)
{
    stub_id = loader;
    imageViews.put(imageView, url);
    Bitmap bitmap=memoryCache.get(url);
    if(bitmap!=null)
        imageView.setImageBitmap(bitmap);
    else
    {
        queuePhoto(url, imageView);
        imageView.setImageResource(loader);
    }
}

private void queuePhoto(String url, ImageView imageView)
{
    PhotoToLoad p=new PhotoToLoad(url, imageView);
    executorService.submit(new PhotosLoader(p));
}

private Bitmap getBitmap(String url)
{
    File f=fileCache.getFile(url);

    //from SD cache
    Bitmap b = decodeFile(f);
    if(b!=null)
        return b;

    //from web
    try {
        Bitmap bitmap=null;
        URL imageUrl = new URL(url);
        HttpURLConnection conn = (HttpURLConnection)imageUrl.openConnection();
        conn.setConnectTimeout(30000);
        conn.setReadTimeout(30000);
        conn.setInstanceFollowRedirects(true);
        InputStream is=conn.getInputStream();
        OutputStream os = new FileOutputStream(f);
        Utils.CopyStream(is, os);
        os.close();
        bitmap = decodeFile(f);
        return bitmap;
    } catch (Exception ex){
       ex.printStackTrace();
       return null;
    }
}

//decodes image and scales it to reduce memory consumption
private Bitmap decodeFile(File f){
    try {
        //decode image size
        BitmapFactory.Options o = new BitmapFactory.Options();
        o.inJustDecodeBounds = true;
        BitmapFactory.decodeStream(new FileInputStream(f),null,o);

        //Find the correct scale value. It should be the power of 2.
        final int REQUIRED_SIZE=70;
        int width_tmp=o.outWidth, height_tmp=o.outHeight;
        int scale=1;
        while(true){
            if(width_tmp/2<REQUIRED_SIZE || height_tmp/2<REQUIRED_SIZE)
                break;
            width_tmp/=2;
            height_tmp/=2;
            scale*=2;
        }

        //decode with inSampleSize
        BitmapFactory.Options o2 = new BitmapFactory.Options();
        o2.inSampleSize=scale;
        return BitmapFactory.decodeStream(new FileInputStream(f), null, o2);
    } catch (FileNotFoundException e) {}
    return null;
}

//Task for the queue
private class PhotoToLoad
{
    public String url;
    public ImageView imageView;
    public PhotoToLoad(String u, ImageView i){
        url=u;
        imageView=i;
    }
}

class PhotosLoader implements Runnable {
    PhotoToLoad photoToLoad;
    PhotosLoader(PhotoToLoad photoToLoad){
        this.photoToLoad=photoToLoad;
    }

    @Override
    public void run() {
        if(imageViewReused(photoToLoad))
            return;
        Bitmap bmp=getBitmap(photoToLoad.url);
        memoryCache.put(photoToLoad.url, bmp);
        if(imageViewReused(photoToLoad))
            return;
        BitmapDisplayer bd=new BitmapDisplayer(bmp, photoToLoad);
        Activity a=(Activity)photoToLoad.imageView.getContext();
        a.runOnUiThread(bd);
    }
}

boolean imageViewReused(PhotoToLoad photoToLoad){
    String tag=imageViews.get(photoToLoad.imageView);
    if(tag==null || !tag.equals(photoToLoad.url))
        return true;
    return false;
}

//Used to display bitmap in the UI thread
class BitmapDisplayer implements Runnable
{
    Bitmap bitmap;
    PhotoToLoad photoToLoad;
    public BitmapDisplayer(Bitmap b, PhotoToLoad p){bitmap=b;photoToLoad=p;}
    public void run()
    {
        if(imageViewReused(photoToLoad))
            return;
        if(bitmap!=null)
            photoToLoad.imageView.setImageBitmap(bitmap);
        else
            photoToLoad.imageView.setImageResource(stub_id);
    }
}

public void clearCache() {
    memoryCache.clear();
    fileCache.clear();
}

}

public class MemoryCache {
private Map<String, SoftReference<Bitmap>> cache=Collections.synchronizedMap(new HashMap<String, SoftReference<Bitmap>>());

public Bitmap get(String id){
    if(!cache.containsKey(id))
        return null;
    SoftReference<Bitmap> ref=cache.get(id);
    return ref.get();
}

public void put(String id, Bitmap bitmap){
    cache.put(id, new SoftReference<Bitmap>(bitmap));
}

public void clear() {
    cache.clear();
}
}


public class Utils {
public static void CopyStream(InputStream is, OutputStream os)
{
    final int buffer_size=1024;
    try
    {
        byte[] bytes=new byte[buffer_size];
        for(;;)
        {
          int count=is.read(bytes, 0, buffer_size);
          if(count==-1)
              break;
          os.write(bytes, 0, count);
        }
    }
    catch(Exception ex){}
}
}

并使用 Manifest.xml 作为，..

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.androidhive.imagefromurl"
android:versionCode="1"
android:versionName="1.0" >

<uses-sdk android:minSdkVersion="8" />

<application
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name" >
    <activity
        android:name=".AndroidLoadImageFromURLActivity"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
</application>

<!-- Internet Permissions -->
<uses-permission android:name="android.permission.INTERNET" />

<!-- Permission to write to external storage -->
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

</manifest>

Answer 2

您可以使用以下代码从 Web 下载图像并在 Android 中的 ImageView 中显示它。我在我的应用程序中尝试它..

public static void DownloadFile(String imageURL, String fileName) throws IOException {
    URL url = new URL(imageURL);
    File file = new File(fileName);

    long startTime = System.currentTimeMillis();
    Log.d("DownloadFile", "Begin Download URL: " + url + " Filename: " + fileName);
    URLConnection ucon = url.openConnection();
    InputStream is = ucon.getInputStream();
    BufferedInputStream bis = new BufferedInputStream(is);
    ByteArrayBuffer baf = new ByteArrayBuffer(50);
    int current = 0;
    while ((current = bis.read()) != -1)
        baf.append((byte) current);
    FileOutputStream fos = new FileOutputStream(file);
    fos.write(baf.toByteArray());
    fos.close();
    Log.d("DownloadFile", "File was downloaded in: " + ((System.currentTimeMillis() - startTime) / 1000) + "s");
}

[...]

try {
    String imagePath = getFilesDir() + "/" + "logo1w.png";
    DownloadFile("http://www.google.de/intl/en_com/images/srpr/logo1w.png", imagePath);
} catch (IOException e) {
    // Something went wrong here
}

ImageView1.setbMap(BitmapFactory.decodeFile(imagePath));