线程，loadImageFromNetwork - 不幸<application>已停止

Question

我的应用程序不会给出任何编译时错误，并且它确实显示了它显示的活动。这是一个简单的按钮活动。当用户点击它时，它应该从网络下载图像。当我点击按钮时，它只是说，“不幸的是，并发已停止。”

我正在阅读android中的线程，并且了解了不在UI线程中执行密集操作并且不从UI线程外部操作UI的规则。我正在练习这个。

我还不熟悉如何阅读logcats。我发布我的logcat，如果有人可以阅读并指出导致问题的原因，那将是非常好的。

此外，loadImageFromNetwork（）的实现不是由我编码的。我只是从互联网复制它。所以我没有理解它对decodeStream（）方法的调用。这一刻我不担心。

Main.java:-

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.Bundle; 
import android.widget.ImageView; 

public class MainActivity extends Activity { 
    public static final String key_name="com.practice.firstApp.key"; 
    ImageView imageView; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 
    } 

    public void downloadImage(){ 
     new Thread(new Runnable(){ 

      private Bitmap loadImageFromNetwork(String url){ 
       try { 
       Bitmap bitmap = BitmapFactory.decodeStream((InputStream)new URL(url).getContent()); 
       return bitmap; 
       } catch (Exception e) { 
       e.printStackTrace(); 
       } 
       return null; 
       } 

      public void run(){ 
       final Bitmap bitmap= loadImageFromNetwork("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"); 
       imageView.post(new Runnable(){ 
        public void run(){ 
         imageView.setImageBitmap(bitmap); 
        } 
       }); 
      } 
     }).start(); 
    } 
} 

activity_main.xml中： -

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:tools="http://schemas.android.com/tools" 

    android:layout_width="match_parent" 
    android:layout_height="match_parent" 

    tools:context=".MainActivity" > 

    <Button 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 

     android:text="@string/Button_MainActivity" 

     android:onClick="downloadImage"/> 

</RelativeLayout> 

String.xml： -

<?xml version="1.0" encoding="utf-8"?> 
<resources> 

    <string name="app_name">Concurrency</string> 
    <string name="action_settings">Settings</string> 
    <string name="hello_world">Hello world!</string> 
    <string name="Button_MainActivity">Download</string> 

</resources> 

的Manifest.xml： -

<?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-sdk 
     android:minSdkVersion="8" 
     android:targetSdkVersion="18" /> 

    <application 
     android:allowBackup="true" 
     android:icon="@drawable/ic_launcher" 
     android:label="@string/app_name" 
     android:theme="@style/AppTheme" > 
     <activity 
      android:name="com.example.concurrency.MainActivity" 
      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> 

logcat的： -

它超出了这个问题的长度。所以你可以找到它here。

Answer 1

您的downloadImage函数需要将View作为参数。补充一点，它应该修正错误

Answer 2

您需要添加下面这行去为你的应用程序访问网络权限......活动内AsynchTask功能

<uses-permission android:name="android.permission.INTERNET" /> 
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" /> 
    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" /> 

接入方法.. ..

BitmapWorkerTask backPropcess = new BitmapWorkerTask(position, ht, 
         wt); 
       backPropcess.executeOnExecutor(AsyncTask.SERIAL_EXECUTOR, urls); 

这是一个下载的AsyncTask类

  public BitmapWorkerTask() { 

       } 

       @Override 
       protected Bitmap doInBackground(String... params) { 
            URL url; 
         try { 
          url = new URL(params[0]); 

           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]); 
             if (bitmap != null && position != null) { 
              addBitmapToMemoryCache(position, bitmap); 
              System.out.println(position); 

          } 
         } catch (MalformedURLException e) { 
          // e.printStackTrace(); 
         } catch (IOException e) { 
          // e.printStackTrace(); 
         } 


        return bitmap; 
       } 

       @Override 
       protected void onPostExecute(Bitmap result) { 
        imageView.setImageBitmap(result); 
       } 
       } 

Answer 3

你可以使用的AsyncTask或下面的代码

private Handler mhHandler = new Handler() { 
    public void handleMessage(android.os.Message msg) { 
     if (msg.what == 100 && msg.obj != null) { 
      imageView.setImageBitmap((Bitmap) msg.obj); 
     } 
    }; 
}; 

public void downloadImage(View v) { 
    new Thread(new Runnable() { 
     private Bitmap loadImageFromNetwork(String url) { 
      try { 
       Bitmap bitmap = BitmapFactory 
         .decodeStream((InputStream) new URL(url) 
           .getContent()); 
       return bitmap; 
      } catch (Exception e) { 
       e.printStackTrace(); 
      } 
      return null; 
     } 

     public void run() { 
      final Bitmap bitmap = loadImageFromNetwork("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"); 
      Message msg = new Message(); 
      msg.what = 100; 
      msg.obj = bitmap; 
      mhHandler.sendMessage(msg); 
     } 
    }).start(); 
} 

，不要忘记把观法downloadImage（视图V）的参数，因为你在呼唤它从布局的onclick。

Answer 4

添加

<uses-permission android:name="android.permission.INTERNET" /> 

同时添加类型的参数 “视图” 你downloadImage功能。

Answer 5

private Bitmap loadImageFromNetwork(String src) { 
    try { 
     URL url = new URL(src); 
     HttpURLConnection connection = (HttpURLConnection) url.openConnection(); 
     connection.setDoInput(true); 
     connection.connect(); 
     InputStream input = connection.getInputStream(); 
     return BitmapFactory.decodeStream(input); 
    } catch (IOException e) { 
     Bitmap icon = BitmapFactory.decodeResource(context.getResources(), R.mipmap.ic_launcher); 
     e.printStackTrace(); 
     return icon; 
    } 
}