我正在开发我的第一个 Android 应用程序。我需要在我的应用程序中显示来自网址的图像。我尝试了以下方法:
主要 Activity 文件:
public class MainViewActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main_view);
int loader = R.drawable.loader;
// Imageview to show
ImageView image = (ImageView) findViewById(R.id.image);
// Image url
String image_url = "http://..../landing.png";
// ImageLoader class instance
ImageLoader imgLoader = new ImageLoader(getApplicationContext());
imgLoader.DisplayImage(image_url, loader, image);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.activity_main_view, menu);
return true;
}
}
这里我在 int loader = R.drawable.loader; 行中收到错误
类文件是:
文件缓存.java
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();
}
}
ImageLoader.java
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();
}
}
MemoryCache.java
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();
}
}
Utils.java
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){}
}
}
请帮助修复该错误并查看我的代码中是否存在任何问题。我已在 list 文件中设置了所需的权限。
最佳答案
您好，我希望这个答案对您有很大帮助，我设计这个项目是为了从网址下载图像并将其存储在缓存中，您可以在您的项目中使用特定的图像。祝您一切顺利如果您有任何疑问 在该项目中，您将评论我，我将解释该项目中的每一步...... 祝一切顺利...
public class MainActivity extends Activity {
private ImageView button;
private BitmapFactory.Options mBitmapOptions;
private Bitmap mBitmap;
private TextView mTime;
private ProgressBar bar;
private LruCache<String, Bitmap> mMemoryCache;
private SeekBar seekbar;
private Button change;
@SuppressLint("NewApi")
@TargetApi(Build.VERSION_CODES.HONEYCOMB_MR1)
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
button = (ImageView) findViewById(R.id.logo);
mTime = (TextView) findViewById(R.id.time);
bar = (ProgressBar) findViewById(R.id.bar);
seekbar = (SeekBar) findViewById(R.id.seekbar);
change = (Button) findViewById(R.id.change);
mBitmapOptions = new BitmapFactory.Options();
mBitmapOptions.inJustDecodeBounds = true;
BitmapFactory.decodeResource(getResources(), R.drawable.ic_launcher,
mBitmapOptions);
mBitmap = Bitmap.createBitmap(mBitmapOptions.outWidth,
mBitmapOptions.outHeight, Config.ARGB_8888);
mBitmapOptions.inJustDecodeBounds = false;
mBitmapOptions.inBitmap = mBitmap;
mBitmapOptions.inSampleSize = 1;
BitmapFactory.decodeResource(getResources(), R.drawable.ic_launcher,
mBitmapOptions);
button.setImageBitmap(mBitmap);
// Use 1/8th of the available memory for this memory cache.
final int cacheSize = 20 * 1024 * 1024;
mMemoryCache = new LruCache<String, Bitmap>(cacheSize) {
@TargetApi(Build.VERSION_CODES.HONEYCOMB_MR1)
@Override
protected int sizeOf(String key, Bitmap bitmap) {
// The cache size will be measured in kilobytes rather than
// number of items.
return bitmap.getByteCount();
}
};
int i = 0;
System.out.println(mMemoryCache.size());
System.out.println(mMemoryCache.evictionCount());
bar.setMax(Images.imageThumbUrls.length - 1);
seekbar.setMax(Images.imageThumbUrls.length - 1);
bar.setProgress(0);
seekbar.setProgress(0);
for (String string : Images.imageUrls) {
String position = String.valueOf(i);
BitmapWorkerTask task = new BitmapWorkerTask(position);
task.executeOnExecutor(AsyncTask.SERIAL_EXECUTOR, string);
i++;
}
seekbar.setOnSeekBarChangeListener(new OnSeekBarChangeListener() {
@Override
public void onStopTrackingTouch(SeekBar seekBar) {
}
@Override
public void onStartTrackingTouch(SeekBar seekBar) {
}
@Override
public void onProgressChanged(SeekBar seekBar, int progress,
boolean fromUser) {
if (Images.imageUrls.length > progress) {
if (getBitmapFromMemCache(String.valueOf(progress)) != null) {
button.setImageBitmap(getBitmapFromMemCache(String
.valueOf(progress)));
} else {
// BitmapWorkerTask task = new
// BitmapWorkerTask(String.valueOf(progress));
// task.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR,Images.imageUrls[progress]);
}
}
}
});
change.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
mMemoryCache.evictAll();
System.out.println(mMemoryCache.size());
System.out.println(mMemoryCache.evictionCount());
bar.setMax(Images.imageUrls.length - 1);
seekbar.setMax(Images.imageThumbUrls.length - 1);
bar.setProgress(0);
seekbar.setProgress(0);
int i = 0;
for (String string : Images.imageUrls) {
String position = String.valueOf(i);
BitmapWorkerTask task = new BitmapWorkerTask(position);
task.executeOnExecutor(AsyncTask.SERIAL_EXECUTOR, string);
i++;
}
}
});
}
@SuppressLint("NewApi")
public void addBitmapToMemoryCache(String position, Bitmap bitmap) {
if (getBitmapFromMemCache(position) == null) {
mMemoryCache.put(position, bitmap);
}
}
public void loadBitmap(int resId, ImageView imageView) {
final String imageKey = String.valueOf(resId);
final Bitmap bitmap = getBitmapFromMemCache(imageKey);
if (bitmap != null) {
button.setImageBitmap(bitmap);
} else {
button.setImageResource(R.drawable.ic_launcher);
}
}
@SuppressLint("NewApi")
public Bitmap getBitmapFromMemCache(String imageKey) {
return mMemoryCache.get(imageKey);
}
class BitmapWorkerTask extends AsyncTask<String, Void, Bitmap> {
private String position = null;
// Decode image in background.
public BitmapWorkerTask(String position) {
this.position = position;
}
@Override
protected Bitmap doInBackground(String... params) {
URL url;
try {
url = new URL(params[0]);
HttpURLConnection connection = (HttpURLConnection) url
.openConnection();
connection.setConnectTimeout(200);
connection.setReadTimeout(1000);
int v = connection.getContentLength() > 0 ? connection
.getContentLength() : 0;
if (v > 0) {
InputStream in = new BufferedInputStream(
connection.getInputStream(), 32 * 1024);
return decodeSampledBitmapFromResource(in, 1000, 1000);
}
} catch (MalformedURLException e) {
//e.printStackTrace();
} catch (IOException e) {
//e.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(Bitmap result) {
if (result != null) {
addBitmapToMemoryCache(position, result);
// button.setImageBitmap(getBitmapFromMemCache(position));
mTime.setText(position);
bar.setProgress(Integer.parseInt(position));
// System.out.println(result);
}
}
}
public Bitmap decodeSampledBitmapFromResource(InputStream in, int reqWidth,
int reqHeight) throws IOException {
// First decode with inJustDecodeBounds=true to check dimensions
final BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
in.mark(in.available());
BitmapFactory.decodeStream(in, null, options);
// Calculate inSampleSize
options.inSampleSize = calculateInSampleSize(options, reqWidth,
reqHeight);
in.reset();
// Decode bitmap with inSampleSize set
options.inJustDecodeBounds = false;
return BitmapFactory.decodeStream(in, null, options);
}
public static int calculateInSampleSize(BitmapFactory.Options options,
int reqWidth, int reqHeight) {
// Raw height and width of image
final int height = options.outHeight;
final int width = options.outWidth;
int inSampleSize = 1;
if (height > reqHeight || width > reqWidth) {
final int halfHeight = height / 2;
final int halfWidth = width / 2;
// Calculate the largest inSampleSize value that is a power of 2 and
// keeps both
// height and width larger than the requested height and width.
while ((halfHeight / inSampleSize) > reqHeight
&& (halfWidth / inSampleSize) > reqWidth) {
inSampleSize *= 2;
}
}
return inSampleSize;
}
}
关于java - 如何在android中显示来自url的图像，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/22603963/