HttpClient連接到互聯網;錯誤打開跟蹤文件：沒有這樣的文件或目錄（2）

Question

我想訪問一個網站，並把HTML源代碼到TextView中。我的模擬器上的瀏覽器正常工作，但我相信在我的應用程序中訪問互聯網的功能不正常。我想我可能不得不使用AsyncTask，但我不知道如何正確實現，或者我甚至不得不使用它。我對編程非常陌生，並且一直在這個網站上尋找一段時間，但似乎無法弄清楚。

這是主代碼：

@Override 
protected void onCreate(Bundle savedInstanceState) { 

super.onCreate(savedInstanceState); 
setContentView(R.layout.activity_main); 
TextView httpTest = (TextView) findViewById(R.id.textView1); 
GetTest sourceCode = new GetTest(); 
String returned; 
try { 
    returned = sourceCode.getInternetData(); 
    httpTest.setText(returned); 

} catch (Exception e) { 
    // TODO Auto-generated catch block 
    e.printStackTrace(); 
    } 
} 

這裏是應該得到的HTML源代碼的代碼：

public class GetTest { 

public String getInternetData() throws Exception { 
    BufferedReader in = null; 
    String data = null; 
    try { 
     HttpClient client = new DefaultHttpClient(); 
     URI website = new URI(
       "http://www.yahoo.com"); 
     HttpGet request = new HttpGet(); 
     request.setURI(website); 
     HttpResponse response = client.execute(request); 
     in = new BufferedReader(new InputStreamReader(response.getEntity() 
       .getContent())); 
     StringBuffer sb = new StringBuffer(""); 
     String l = ""; 
     String nl = System.getProperty("line.separator"); 
     while ((l = in.readLine()) != null) { 
      sb.append(l + nl); 
     } 
     in.close(); 
     data = sb.toString(); 
     return data; 
    } finally { 
     if (in != null) { 
      try { 
       in.close(); 
       return data; 
      } catch (Exception e) { 
       e.printStackTrace(); 
      } 
     } 
    } 
    } 
    } 

我的清單中的權限：

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

最後，這裏是我的logcat：

04-30 02:28:44.368: E/Trace(1095):  error opening trace file: No such file or directory (2) 
04-30 02:28:45.338: D/dalvikvm(1095):  GC_FOR_ALLOC freed 51K, 7% free 2555K/2728K, paused 41ms, total 44ms 
04-30 02:28:45.348: I/dalvikvm-heap(1095): Grow heap (frag case) to 3.216MB for 635812-byte allocation 
04-30 02:28:45.398: D/dalvikvm(1095):  GC_FOR_ALLOC freed 2K, 6% free 3174K/3352K, paused 45ms, total 45ms 
04-30 02:28:45.447: D/dalvikvm(1095):  GC_CONCURRENT freed <1K, 6% free 3177K/3352K, paused 5ms+4ms, total 57ms 
04-30 02:28:45.509: W/System.err(1095):  android.os.NetworkOnMainThreadException 
04-30 02:28:45.509: W/System.err(1095):  at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1117) 
04-30 02:28:45.509: W/System.err(1095):  at java.net.InetAddress.lookupHostByName(InetAddress.java:385) 
04-30 02:28:45.509: W/System.err(1095):  at java.net.InetAddress.getAllByNameImpl(InetAddress.java:236) 
04-30 02:28:45.509: W/System.err(1095):  at java.net.InetAddress.getAllByName(InetAddress.java:214) 
04-30 02:28:45.518: W/System.err(1095):  at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:137) 
04-30 02:28:45.518: W/System.err(1095):  at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:164) 
04-30 02:28:45.518: W/System.err(1095):  at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:119) 
04-30 02:28:45.518: W/System.err(1095):  at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:360) 
04-30 02:28:45.518: W/System.err(1095):  at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:555) 
04-30 02:28:45.528: W/System.err(1095):  at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:487) 
04-30 02:28:45.528: W/System.err(1095):  at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:465) 
04-30 02:28:45.528: W/System.err(1095):  at com.example.edittexttest.GetTest.getInternetData(GetTest.java:24) 
04-30 02:28:45.528: W/System.err(1095):  at com.example.edittexttest.MainActivity.onCreate(MainActivity.java:18) 
04-30 02:28:45.528: W/System.err(1095):  at android.app.Activity.performCreate(Activity.java:5104) 
04-30 02:28:45.528: W/System.err(1095):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080) 
04-30 02:28:45.528: W/System.err(1095):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144) 
04-30 02:28:45.528: W/System.err(1095):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230) 
04-30 02:28:45.528: W/System.err(1095):  at android.app.ActivityThread.access$600(ActivityThread.java:141) 
04-30 02:28:45.528: W/System.err(1095):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234) 
04-30 02:28:45.538: W/System.err(1095):  at android.os.Handler.dispatchMessage(Handler.java:99) 
04-30 02:28:45.538: W/System.err(1095):  at android.os.Looper.loop(Looper.java:137) 
04-30 02:28:45.538: W/System.err(1095):  at android.app.ActivityThread.main(ActivityThread.java:5041) 
04-30 02:28:45.538: W/System.err(1095):  at java.lang.reflect.Method.invokeNative(Native Method) 
04-30 02:28:45.538: W/System.err(1095):  at java.lang.reflect.Method.invoke(Method.java:511) 
04-30 02:28:45.538: W/System.err(1095):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 
04-30 02:28:45.538: W/System.err(1095):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 
04-30 02:28:45.548: W/System.err(1095):  at dalvik.system.NativeStart.main(Native Method) 
04-30 02:28:45.758: D/gralloc_goldfish(1095): Emulator without GPU emulation detected. 

感謝您的高級幫助！

Answer 1

您的代碼在主線程中執行聯網操作。如果您的目標是Honeycomb或更高版本（3.0+），則無法在主線程上執行聯網操作。所以，你得到這個：

android.os.NetworkOnMainThreadException

請參閱How to fix android.os.NetworkOnMainThreadException?獲取更多信息。 如果您花一些時間學習如何使用AsyncTask，那將會很棒。 無論如何，下面是如何使用它的粗略代碼。 （我試圖從你的代碼中修改東西。）

public class YoursActivity extends Activity { 

    private TextView httpTest; 
    /** Called when the activity is first created. */ 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 
     httpTest = (TextView) findViewById(R.id.textView1); 
     new HttpTask().execute(); 
     ...  
    } 
    ... 

    private class HttpTask extends AsyncTask<String, Void, String> { 

     @Override 
     protected String doInBackground(String... params) { 
      GetTest sourceCode = new GetTest(); 
      String returned = ""; 
      try { 
       returned = sourceCode.getInternetData(); 

      } catch (Exception e) { 
       // TODO Auto-generated catch block 
       e.printStackTrace(); 
      } 
      return returned; 
     }  

     @Override 
     protected void onPostExecute(String returned) { 
      httpTest.setText(returned);     
     } 
    } 

}