我写了以下应用程序，从互联网上下载图像，然后在imageview中显示。但这似乎永远挂了。它是否与互联网的速度有关（它是一个小图像，尺寸为340 * 340像素，并且通常在我通常将其保存在计算机上时没有时间），或者代码是否有问题？
package com.example.concurrency;
import java.io.InputStream;
import java.net.URL;
import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Bundle;
import android.widget.ImageView;
public class UsingAsyncTask extends Activity {
ImageView imageView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.using_asynctask);
String spec="http://www.google.com/imgres?imgurl=http%3A%2F%2Fupload.wikimedia.org%2Fwikipedia%2Fcommons%2F7%2F7a%2FBasketball.png&imgrefurl=http%3A%2F%2Fcommons.wikimedia.org%2Fwiki%2FFile%3ABasketball.png&h=340&w=340&tbnid=EJmjEDyJzrhAuM%3A&zoom=1&docid=C_hn8nOgsGmuwM&hl=en&ei=Q0o2U93LNcaIygH4mICQBQ&tbm=isch&ved=0CHwQhBwwBg&iact=rc&dur=3875&page=1&start=0&ndsp=14";
URL params = null;
try {params= new URL(spec);} catch(Exception e) {}
//Bitmap result;
new MyTask().execute(params);
imageView= (ImageView) findViewById(R.id.imageview);
}
private class MyTask extends AsyncTask<URL, Void, Bitmap> {
private Bitmap loadImageFromNetwork(String url){
try {
Bitmap bitmap = BitmapFactory.decodeStream((InputStream)new URL(url).getContent());
return bitmap;
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
/*protected void onPreExecute() {
}*/
@Override
protected Bitmap doInBackground(URL... params){
//if(isCancelled()) return;
String url=params[0].toString();
final Bitmap bitmap= loadImageFromNetwork(url);
return bitmap;
}
/*protected void onProgressUpdate(Progress progress){
setProgressPercent(progress[0]);
}*/
@Override
protected void onPostExecute(Bitmap result){
imageView.setImageBitmap(result);
}
}
}
清单文件： -
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.concurrency"
android:versionCode="1"
android:versionName="1.0" >
<uses-permission android:name="android.permission.INTERNET"></uses-permission>
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="19" />
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="com.example.concurrency.UsingAsyncTask"
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>
</manifest>
布局： -
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<ProgressBar
android:id="@+id/progressbar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:padding="4dip"
android:indeterminate="false"
android:max="10"/>
<ImageView
android:id="@+id/imageview"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:padding="4dip"
android:contentDescription="@string/imageview"/>
</LinearLayout>
答案 0 :(得分：1)
我认为您使用的是Google图片搜索网址，它可能需要更长时间才能阅读。我在下面提到了图像实际链接。请使用此直接链接，以便更快/更好地加载。
因为Google可能需要三次或请求，但这是该文件的直接链接，这就是原因....
http://upload.wikimedia.org/wikipedia/commons/7/7a/Basketball.png
然后使用这种方法从Url中读取图像......
public static class BitmapWorkerTask extends
AsyncTask<String, Void, Bitmap> {
private int ht;
private int wt;
// Decode image in background.
public BitmapWorkerTask(int progress, int ht, int wt) {
this.ht = ht;
this.wt = wt;
}
@Override
protected Bitmap doInBackground(String... params) {
URL url;
try {
url = new URL(string);
if (getBitmapFromMemCache(position) == null) {
HttpURLConnection connection = (HttpURLConnection) url
.openConnection();
connection.setConnectTimeout(4000);
connection.setReadTimeout(10000);
int v = connection.getContentLength() > 0 ? connection
.getContentLength() : 0;
if (v > 0) {
InputStream in = new BufferedInputStream(
connection.getInputStream(), 32 * 1024);
Bitmap bitmap = decodeSampledBitmapFromResource(
in, ht[i], wt[i]);
} catch (MalformedURLException e) {
// e.printStackTrace();
} catch (IOException e) {
// e.printStackTrace();
}
}
return bitmap ;
}
@Override
protected void onPostExecute(Bitmap result) {
//Do your bitmap image setting....
//image.setImageBitmap(bitmap);
}
}
以下方法用于避免内存不足异常....这对于高处理中的图像非常有用...
public static 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;
}
答案 1 :(得分：1)
问题在于spec字符串传递给AsyncTask。它指的是HTML页面，而不是图像本身，这就是为什么您无法将InputStream解码为Bitmap的原因。将spec替换为以下值http://upload.wikimedia.org/wikipedia/commons/7/7a/Basketball.png。我测试了这个变化并且它有效。另请注意，如果您在代理服务器后面的模拟器上进行测试，则必须指定代理设置。