我想缓存我通过互联网获取的图片。 因此，每次在图库中刷图像时，它们都不会每次都被取出。如果有人能告诉我如何用这段代码做到这一点，我们将不胜感激。
if(Build.VERSION.SDK_INT >= 11){
StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
StrictMode.setThreadPolicy(policy);
}
my.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
startActivity(n);
}
});
gameNews.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
}
});
//Executing AsyncTask in background thread to get images.
MyTask myTask = new MyTask();
myTask.execute();
}
获取图像方法：
//Method to get images from text documents that will by updated every month.
public void getImages() throws IOException{
DefaultHttpClient httpclient = new DefaultHttpClient();
HttpGet httppost = new HttpGet("https://sites.google.com/site/theitrangers/images/webImages.txt");
HttpResponse response;
response = httpclient.execute(httppost);
HttpEntity ht = response.getEntity();
BufferedHttpEntity buf = new BufferedHttpEntity(ht);
InputStream is = buf.getContent();
BufferedReader r = new BufferedReader(new InputStreamReader(is));
StringBuilder total = new StringBuilder();
String line;
while ((line = r.readLine()) != null) {
total.append(line + "\n");
imageUrl = total.toString();
Log.v("getImage1", "Retreived image");
}
}
public void getImage2() throws IOException{
DefaultHttpClient httpclient = new DefaultHttpClient();
HttpGet httppost = new HttpGet("https://sites.google.com/site/theitrangers/images/webImage2.txt");
HttpResponse response;
response = httpclient.execute(httppost);
HttpEntity ht = response.getEntity();
BufferedHttpEntity buf = new BufferedHttpEntity(ht);
InputStream is = buf.getContent();
BufferedReader r = new BufferedReader(new InputStreamReader(is));
StringBuilder total = new StringBuilder();
String line;
while ((line = r.readLine()) != null) {
total.append(line + "\n");
imageUrl2 = total.toString();
Log.v("getImage2", "Retreived image");
}
}
public void getImage3() throws IOException{
DefaultHttpClient httpclient = new DefaultHttpClient();
HttpGet httppost = new HttpGet("https://sites.google.com/site/theitrangers/images/webimage3.txt");
HttpResponse response;
response = httpclient.execute(httppost);
HttpEntity ht = response.getEntity();
BufferedHttpEntity buf = new BufferedHttpEntity(ht);
InputStream is = buf.getContent();
BufferedReader r = new BufferedReader(new InputStreamReader(is));
StringBuilder total = new StringBuilder();
String line;
while ((line = r.readLine()) != null) {
total.append(line + "\n");
imageUrl3 = total.toString();
Log.v("getImage3", "Retreived image");
}
}
public void getImage4() throws IOException{
DefaultHttpClient httpclient = new DefaultHttpClient();
HttpGet httppost = new HttpGet("https://sites.google.com/site/theitrangers/images/webImage4.txt");
HttpResponse response;
response = httpclient.execute(httppost);
HttpEntity ht = response.getEntity();
BufferedHttpEntity buf = new BufferedHttpEntity(ht);
InputStream is = buf.getContent();
BufferedReader r = new BufferedReader(new InputStreamReader(is));
StringBuilder total = new StringBuilder();
String line;
while ((line = r.readLine()) != null) {
total.append(line + "\n");
imageUrl4 = total.toString();
}
}
ImageAdapter类：
//ImageAdapter that gets the URL of the images and put them in a format to be set to gallery
public class ImageAdapter extends BaseAdapter {
/** The parent context */
private Context myContext;public ImageAdapter() {
// TODO Auto-generated constructor stub
}
/** URL-Strings to some remote images. */
public String[] myRemoteImages = {imageUrl,imageUrl2,imageUrl3,imageUrl4};
/** Simple Constructor saving the 'parent' context. */
public ImageAdapter(Context c) { this.myContext = c; }
/** Returns the amount of images we have defined. */
public int getCount() { return this.myRemoteImages.length; }
/* Use the array-Positions as unique IDs */
public Object getItem(int position) { return position; }
public long getItemId(int position) { return position; }
/** Returns a new ImageView to
* be displayed, depending on
* the position passed. */
public View getView(int position, View convertView, ViewGroup parent) {
ImageView i = new ImageView(this.myContext);
try {
URL aURL = new URL(myRemoteImages[position]);
URLConnection conn = aURL.openConnection();
conn.connect();
InputStream is = conn.getInputStream();
/* Buffered is always good for a performance plus. */
BufferedInputStream bis = new BufferedInputStream(is);
/* Decode url-data to a bitmap. */
Bitmap bm = BitmapFactory.decodeStream(bis);
bis.close();
is.close();
Log.v(imageUrl, "Retrieving image");
/* Apply the Bitmap to the ImageView that will be returned. */
i.setImageBitmap(bm);
} catch (IOException e) {
Log.e("DEBUGTAG", "Remtoe Image Exception", e);
}
/* Image should be scaled as width/height are set. */
i.setScaleType(ImageView.ScaleType.FIT_CENTER);
/* Set the Width/Height of the ImageView. */
i.setLayoutParams(new Gallery.LayoutParams(150, 150));
return i;
}
/** Returns the size (0.0f to 1.0f) of the views
* depending on the 'offset' to the center. */
public float getScale(boolean focused, int offset) {
/* Formula: 1 / (2 ^ offset) */
return Math.max(0, 1.0f / (float)Math.pow(2, Math.abs(offset)));
}
}
//the important AsyncTask method. running the background thread to get the images and set them to the gallery.
private class MyTask extends AsyncTask<Void, Void, Void>{
@Override
protected Void doInBackground(Void... arg0) {try {
getImages();
Log.v("MyTask", "Image 1 retreived");
getImage2();
Log.v("MyTask", "Image 2 retreived");
getImage3();
Log.v("MyTask", "Image 3 retreived");
getImage4();
Log.v("MyTask", "Image 4 retreived");
} catch (IOException e) {
Log.e("MainMenu retreive image", "Image Retreival failed");
e.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(Void notUsed){
((Gallery) findViewById(R.id.gallery))
.setAdapter(new ImageAdapter(MainMenu.this));
}
}
答案 0 :(得分：1)
有几种方法可以做到这一点，假设网址中的文件名是唯一的，您可以将它们写入SD卡或内部存储。例如：
File cacheDir = new File("my-cache-dir");
File[] fileList = cacheDir.listFiles();
int index = linearSearch.(fileList, uri.getFileName());
if(index != -1){
// load from file
} else {
// load from web
}
还有其他几种方法可以做到这一点，例如使用数据库或平面文件。请记住，每次缓存的内容都必须生成相同的缓存密钥。