Android初学第90天
Android初学第90天
26_Handlers
代码
PhotoGallery
ThumbnailDownloader.java
package com.bignerdranch.android.photogallery;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Handler;
import android.os.HandlerThread;
import android.os.Message;
import android.util.Log;
import java.io.IOException;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
public class ThumbnailDownloader<T> extends HandlerThread {
private static final String TAG = "ThumbnailDownloader";
private static final int MESSAGE_DOWNLOAD = 0;
private boolean mHasQuit = false;
private Handler mRequestHandler;
private ConcurrentMap<T,String> mRequestMap = new ConcurrentHashMap<>();
private Handler mResponseHandler;
private ThumbnailDownloadListener<T> mThumbnailDownloadListener;
public interface ThumbnailDownloadListener<T> {
void onThumbnailDownloaded(T target, Bitmap bitmap);
}
public void setThumbnailDownloadListener(ThumbnailDownloadListener<T> listener) {
mThumbnailDownloadListener = listener;
}
public ThumbnailDownloader(Handler responseHandler) {
super(TAG);
mResponseHandler = responseHandler;
}
@Override
protected void onLooperPrepared() {
mRequestHandler = new Handler() {
@Override
public void handleMessage(Message msg) {
if (msg.what == MESSAGE_DOWNLOAD) {
T target = (T) msg.obj;
Log.i(TAG, "Got a request for URL: " + mRequestMap.get(target));
handleRequest(target);
}
}
};
}
@Override
public boolean quit() {
mHasQuit = true;
return super.quit();
}
public void queueThumbnail(T target, String url) {
Log.i(TAG, "Got a URL: " + url);
if (url == null) {
mRequestMap.remove(target);
} else {
mRequestMap.put(target, url);
mRequestHandler.obtainMessage(MESSAGE_DOWNLOAD, target)
.sendToTarget();
}
}
public void clearQueue() {
mRequestHandler.removeMessages(MESSAGE_DOWNLOAD);
mRequestMap.clear();
}
private void handleRequest(final T target) {
try {
final String url = mRequestMap.get(target);
if (url == null) {
return;
}
byte[] bitmapBytes = new FlickrFetchr().getUrlBytes(url);
final Bitmap bitmap = BitmapFactory
.decodeByteArray(bitmapBytes, 0, bitmapBytes.length);
Log.i(TAG, "Bitmap created");
mResponseHandler.post(new Runnable() {
public void run() {
if (mRequestMap.get(target) != url ||
mHasQuit) {
return;
}
mRequestMap.remove(target);
mThumbnailDownloadListener.onThumbnailDownloaded(target, bitmap);
}
});
} catch (IOException ioe) {
Log.e(TAG, "Error downloading image", ioe);
}
}
}