我正在使用ListView来显示与这些图像相关的一些图像和标题。我正在从互联网上获取图像。是否有一种方法可以延迟加载图像,以便在文本显示时,UI不会被阻止,图像在下载时显示?
图像总数不是固定的。
我正在使用ListView来显示与这些图像相关的一些图像和标题。我正在从互联网上获取图像。是否有一种方法可以延迟加载图像,以便在文本显示时,UI不会被阻止,图像在下载时显示?
图像总数不是固定的。
当前回答
以下是我创建的用于保存应用程序当前显示的图像的内容。请注意,这里使用的“Log”对象是我对Android中最终Log类的自定义包装。
package com.wilson.android.library;
/*
Licensed to the Apache Software Foundation (ASF) under one or more
contributor license agreements. See the NOTICE file
distributed with this work for additional information
regarding copyright ownership. The ASF licenses this file
to you under the Apache License, Version 2.0 (the
"License"); you may not use this file except in compliance
with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing,
software distributed under the License is distributed on an
"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
KIND, either express or implied. See the License for the
specific language governing permissions and limitations
under the License.
*/
import java.io.IOException;
public class DrawableManager {
private final Map<String, Drawable> drawableMap;
public DrawableManager() {
drawableMap = new HashMap<String, Drawable>();
}
public Drawable fetchDrawable(String urlString) {
if (drawableMap.containsKey(urlString)) {
return drawableMap.get(urlString);
}
Log.d(this.getClass().getSimpleName(), "image url:" + urlString);
try {
InputStream is = fetch(urlString);
Drawable drawable = Drawable.createFromStream(is, "src");
if (drawable != null) {
drawableMap.put(urlString, drawable);
Log.d(this.getClass().getSimpleName(), "got a thumbnail drawable: " + drawable.getBounds() + ", "
+ drawable.getIntrinsicHeight() + "," + drawable.getIntrinsicWidth() + ", "
+ drawable.getMinimumHeight() + "," + drawable.getMinimumWidth());
} else {
Log.w(this.getClass().getSimpleName(), "could not get thumbnail");
}
return drawable;
} catch (MalformedURLException e) {
Log.e(this.getClass().getSimpleName(), "fetchDrawable failed", e);
return null;
} catch (IOException e) {
Log.e(this.getClass().getSimpleName(), "fetchDrawable failed", e);
return null;
}
}
public void fetchDrawableOnThread(final String urlString, final ImageView imageView) {
if (drawableMap.containsKey(urlString)) {
imageView.setImageDrawable(drawableMap.get(urlString));
}
final Handler handler = new Handler(Looper.getMainLooper()) {
@Override
public void handleMessage(Message message) {
imageView.setImageDrawable((Drawable) message.obj);
}
};
Thread thread = new Thread() {
@Override
public void run() {
//TODO : set imageView to a "pending" image
Drawable drawable = fetchDrawable(urlString);
Message message = handler.obtainMessage(1, drawable);
handler.sendMessage(message);
}
};
thread.start();
}
private InputStream fetch(String urlString) throws MalformedURLException, IOException {
DefaultHttpClient httpClient = new DefaultHttpClient();
HttpGet request = new HttpGet(urlString);
HttpResponse response = httpClient.execute(request);
return response.getEntity().getContent();
}
}
其他回答
我只想再添加一个很好的示例,XML适配器。由于它被谷歌使用,我也在使用相同的逻辑来避免OutOfMemory错误。
基本上,这个ImageDownloader就是你的答案(因为它涵盖了你的大部分需求)。有些也可以在其中实现。
如果你想像Facebook一样显示Shimmer布局,有一个官方的Facebook库。FaceBook Shimmer Android
它可以处理所有的事情,你只需要将你想要的设计代码以嵌套的方式放在闪闪发光的框架中。这是一个示例代码。
<com.facebook.shimmer.ShimmerFrameLayout
android:id=“@+id/shimmer_view_container”
android:layout_width=“wrap_content”
android:layout_height="wrap_content"
shimmer:duration="1000">
<here will be your content to display />
</com.facebook.shimmer.ShimmerFrameLayout>
这是它的java代码。
ShimmerFrameLayout shimmerContainer = (ShimmerFrameLayout) findViewById(R.id.shimmer_view_container);
shimmerContainer.startShimmerAnimation();
在渐变文件中添加此相关性。
implementation 'com.facebook.shimmer:shimmer:0.1.0@aar'
这是它的样子。
我认为这个问题在Android开发人员中非常流行,有很多这样的库声称可以解决这个问题,但似乎只有少数库是正确的。AQuery就是一个这样的图书馆,但它在所有方面都比大多数图书馆好,值得一试。
您可以尝试使用Aquery Android库来延迟加载图像和列表视图。。。以下代码可能会帮助您。。。。。从这里下载库。
AQuery aq = new AQuery(mContext);
aq.id(R.id.image1).image("http://data.whicdn.com/images/63995806/original.jpg");
高性能加载器-在检查了这里建议的方法之后,我用了Ben的解决方案-
我意识到使用drawable比使用位图更快,所以我使用了drawable使用SoftReference很好,但它会使缓存的图像太频繁地被删除,所以我添加了一个保存图像引用的链接列表,防止图像被删除,直到达到预定义的大小为了打开InputStream,我使用java.net.URLConnection,它允许我使用web缓存(您需要先设置响应缓存,但这是另一回事)
我的代码:
import java.util.Map;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.Collections;
import java.util.WeakHashMap;
import java.lang.ref.SoftReference;
import java.util.concurrent.Executors;
import java.util.concurrent.ExecutorService;
import android.graphics.drawable.Drawable;
import android.widget.ImageView;
import android.os.Handler;
import android.os.Message;
import java.io.InputStream;
import java.net.MalformedURLException;
import java.io.IOException;
import java.net.URL;
import java.net.URLConnection;
public class DrawableBackgroundDownloader {
private final Map<String, SoftReference<Drawable>> mCache = new HashMap<String, SoftReference<Drawable>>();
private final LinkedList <Drawable> mChacheController = new LinkedList <Drawable> ();
private ExecutorService mThreadPool;
private final Map<ImageView, String> mImageViews = Collections.synchronizedMap(new WeakHashMap<ImageView, String>());
public static int MAX_CACHE_SIZE = 80;
public int THREAD_POOL_SIZE = 3;
/**
* Constructor
*/
public DrawableBackgroundDownloader() {
mThreadPool = Executors.newFixedThreadPool(THREAD_POOL_SIZE);
}
/**
* Clears all instance data and stops running threads
*/
public void Reset() {
ExecutorService oldThreadPool = mThreadPool;
mThreadPool = Executors.newFixedThreadPool(THREAD_POOL_SIZE);
oldThreadPool.shutdownNow();
mChacheController.clear();
mCache.clear();
mImageViews.clear();
}
public void loadDrawable(final String url, final ImageView imageView,Drawable placeholder) {
mImageViews.put(imageView, url);
Drawable drawable = getDrawableFromCache(url);
// check in UI thread, so no concurrency issues
if (drawable != null) {
//Log.d(null, "Item loaded from mCache: " + url);
imageView.setImageDrawable(drawable);
} else {
imageView.setImageDrawable(placeholder);
queueJob(url, imageView, placeholder);
}
}
private Drawable getDrawableFromCache(String url) {
if (mCache.containsKey(url)) {
return mCache.get(url).get();
}
return null;
}
private synchronized void putDrawableInCache(String url,Drawable drawable) {
int chacheControllerSize = mChacheController.size();
if (chacheControllerSize > MAX_CACHE_SIZE)
mChacheController.subList(0, MAX_CACHE_SIZE/2).clear();
mChacheController.addLast(drawable);
mCache.put(url, new SoftReference<Drawable>(drawable));
}
private void queueJob(final String url, final ImageView imageView,final Drawable placeholder) {
/* Create handler in UI thread. */
final Handler handler = new Handler() {
@Override
public void handleMessage(Message msg) {
String tag = mImageViews.get(imageView);
if (tag != null && tag.equals(url)) {
if (imageView.isShown())
if (msg.obj != null) {
imageView.setImageDrawable((Drawable) msg.obj);
} else {
imageView.setImageDrawable(placeholder);
//Log.d(null, "fail " + url);
}
}
}
};
mThreadPool.submit(new Runnable() {
@Override
public void run() {
final Drawable bmp = downloadDrawable(url);
// if the view is not visible anymore, the image will be ready for next time in cache
if (imageView.isShown())
{
Message message = Message.obtain();
message.obj = bmp;
//Log.d(null, "Item downloaded: " + url);
handler.sendMessage(message);
}
}
});
}
private Drawable downloadDrawable(String url) {
try {
InputStream is = getInputStream(url);
Drawable drawable = Drawable.createFromStream(is, url);
putDrawableInCache(url,drawable);
return drawable;
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
private InputStream getInputStream(String urlString) throws MalformedURLException, IOException {
URL url = new URL(urlString);
URLConnection connection;
connection = url.openConnection();
connection.setUseCaches(true);
connection.connect();
InputStream response = connection.getInputStream();
return response;
}
}