無法在靜態上下文中調用動態方法？

這些是使用類似於How to modify dummy content in android master/detail activity?的Android Studio創建的。我改變了靜態方法dummyContent下到下面：無法在靜態上下文中調用動態方法？

public void fetchData() { 
    // Add some sample items. 
    for (int i = 1; i <= COUNT; i++) { 
     addItem(createDummyItem(i)); 
    } 

    Authenticator.setDefault(new Authenticator() { 
     @Override 
     protected PasswordAuthentication getPasswordAuthentication() { 
      return new PasswordAuthentication(
        DummyContent.UNAME, DummyContent.PASSWORD.toCharArray()); 
     } 
    }); 

    try { 
     DummyContentRegistry registry = new XMLDummyContentParser(DummyContent.url).parse(); 
     for (DummyContent.DummyItem t: registry.getTeachers()) { 
      DummyContent.addItem(t); 
     } 
    } catch (Exception e) { 
     fail("Exception should not have been thrown"); 
    } 
}

而上述通過測試：

public class DummyContentRegistryTest { 
    @Before 
    public void buildRegistry() {} 

    @Test 
    public void testFetchData() { 
     Assert.assertEquals(0,DummyContent.ITEMS.size()); 
     new DummyContent().fetchData(); 
     Assert.assertEquals(27,DummyContent.ITEMS.size());// two more items are added through parsing xml on a website 
    } 

}

然而，當我打電話MainActivity.onCreate項下的方法失敗「異常不應該被扔到」。爲什麼？下面是失敗的通話

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    if (DummyContent.ITEMS.isEmpty()) { 
     new DummyContent().fetchData(); 
    } 
...... 
}

我不知道這個問題是類似calling non-static method in static method in Java的例子，但我顯然試圖大多同意的方式。

[ 07-25 04:04:56.442 23983:24025 D/   ] 
                        HostConnection::get() New Host Connection established 0x7f1b57910500, tid 24025 
07-25 04:04:56.460 23983-24025/*****private*****.myapplication I/OpenGLRenderer: Initialized EGL, version 1.4 
07-25 04:04:56.873 23983-23983/*****private*****.myapplication I/Choreographer: Skipped 32 frames! The application may be doing too much work on its main thread. 
07-25 04:05:07.474 23983-23983/*****private*****.myapplication W/System.err: java.io.IOException: Couldn't open *****private***** 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at org.apache.harmony.xml.ExpatParser.openUrl(ExpatParser.java:755) 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at org.apache.harmony.xml.ExpatReader.parse(ExpatReader.java:292) 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at javax.xml.parsers.SAXParser.parse(SAXParser.java:390) 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at javax.xml.parsers.SAXParser.parse(SAXParser.java:266) 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at *****private*****.myapplication.dummy.XMLDummyContentParser.parse(XMLDummyContentParser.java:33) 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at *****private*****.myapplication.dummy.DummyContent.fetchData(DummyContent.java:53) 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at *****private*****.myapplication.MainActivity.onCreate(MainActivity.java:52) 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at android.app.Activity.performCreate(Activity.java:6237) 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107) 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369) 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at android.app.ActivityThread.-wrap11(ActivityThread.java) 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at android.os.Handler.dispatchMessage(Handler.java:102) 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at android.os.Looper.loop(Looper.java:148) 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at android.app.ActivityThread.main(ActivityThread.java:5417) 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at java.lang.reflect.Method.invoke(Native Method) 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err: Caused by: android.os.NetworkOnMainThreadException 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1273) 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at java.net.InetAddress.lookupHostByName(InetAddress.java:431) 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at java.net.InetAddress.getAllByNameImpl(InetAddress.java:252) 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at java.net.InetAddress.getAllByName(InetAddress.java:215) 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at com.android.okhttp.internal.Network$1.resolveInetAddresses(Network.java:29) 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at com.android.okhttp.internal.http.RouteSelector.resetNextInetSocketAddress(RouteSelector.java:188) 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at com.android.okhttp.internal.http.RouteSelector.nextProxy(RouteSelector.java:157) 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at com.android.okhttp.internal.http.RouteSelector.next(RouteSelector.java:100) 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at com.android.okhttp.internal.http.HttpEngine.createNextConnection(HttpEngine.java:357) 
07-25 04:05:07.475 23983-23983/*****private*****.myapplication W/System.err:  at com.android.okhttp.internal.http.HttpEngine.nextConnection(HttpEngine.java:340) 
07-25 04:05:07.476 23983-23983/*****private*****.myapplication W/System.err:  at com.android.okhttp.internal.http.HttpEngine.connect(HttpEngine.java:330) 
07-25 04:05:07.476 23983-23983/*****private*****.myapplication W/System.err:  at com.android.okhttp.internal.http.HttpEngine.sendRequest(HttpEngine.java:248) 
07-25 04:05:07.476 23983-23983/*****private*****.myapplication W/System.err:  at com.android.okhttp.internal.huc.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:433) 
07-25 04:05:07.476 23983-23983/*****private*****.myapplication W/System.err:  at com.android.okhttp.internal.huc.HttpURLConnectionImpl.getResponse(HttpURLConnectionImpl.java:384) 
07-25 04:05:07.476 23983-23983/*****private*****.myapplication W/System.err:  at com.android.okhttp.internal.huc.HttpURLConnectionImpl.getInputStream(HttpURLConnectionImpl.java:231) 
07-25 04:05:07.476 23983-23983/*****private*****.myapplication W/System.err:  at com.android.okhttp.internal.huc.DelegatingHttpsURLConnection.getInputStream(DelegatingHttpsURLConnection.java:210) 
07-25 04:05:07.476 23983-23983/*****private*****.myapplication W/System.err:  at com.android.okhttp.internal.huc.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java) 
07-25 04:05:07.476 23983-23983/*****private*****.myapplication W/System.err:  at org.apache.harmony.xml.ExpatParser.openUrl(ExpatParser.java:753) 
07-25 04:05:07.476 23983-23983/*****private*****.myapplication W/System.err: ... 18 more 
07-25 04:05:07.483 23983-23983/*****private*****.myapplication D/AndroidRuntime: Shutting down VM 


07-25 04:05:07.484 23983-23983/*****private*****.myapplication E/AndroidRuntime: FATAL EXCEPTION: main 
                        Process: ******private*******, PID: 23983 
                        java.lang.RuntimeException: Unable to start activity ComponentInfo{******private*******.myapplication.MainActivity}: java.lang.IllegalStateException: Already attached 
                         at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416) 
                         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
                         at android.app.ActivityThread.-wrap11(ActivityThread.java) 
                         at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
                         at android.os.Handler.dispatchMessage(Handler.java:102) 
                         at android.os.Looper.loop(Looper.java:148) 
                         at android.app.ActivityThread.main(ActivityThread.java:5417) 
                         at java.lang.reflect.Method.invoke(Native Method) 
                         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
                         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
                        Caused by: java.lang.IllegalStateException: Already attached 
                         at android.support.v4.app.FragmentManagerImpl.attachController(FragmentManager.java:2126) 
                         at android.support.v4.app.FragmentController.attachHost(FragmentController.java:104) 
                         at android.support.v4.app.FragmentActivity.onCreate(FragmentActivity.java:313) 
                         at android.support.v7.app.AppCompatActivity.onCreate(AppCompatActivity.java:85) 
                         at *****private*****.myapplication.MainActivity.onCreate(MainActivity.java:55) 
                         at android.app.Activity.performCreate(Activity.java:6237) 
                         at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107) 
                         at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369) 
                         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)  
                         at android.app.ActivityThread.-wrap11(ActivityThread.java)  
                         at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)  
                         at android.os.Handler.dispatchMessage(Handler.java:102)  
                         at android.os.Looper.loop(Looper.java:148)  
                         at android.app.ActivityThread.main(ActivityThread.java:5417)  
                         at java.lang.reflect.Method.invoke(Native Method)  
                         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)  
                         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

來源

2016-07-25 Student

例外e，你可以捕獲它可能包含對究竟是什麼出了問題的有用信息。在catch -block內部執行e.printStackTrace();以將所有可用信息打印到標準輸出。如果這並不能幫助您解決問題，請在這裏發佈堆棧跟蹤。

來源

2016-07-25 11:02:53 kalsowerus

嘿，這是本更新，請看看 – Student

看來你的異常來自'android.os.NetworkOnMainThreadException'。看看這個線程的幫助：[http://stackoverflow.com/questions/6343166/how-to-fix-android-os-networkonmainthreadexception](http://stackoverflow.com/questions/6343166/how-to - 修復功能的Android-OS-networkonmainthreadexception） – kalsowerus

你不能操縱UI thread從background thread這就是爲什麼你得到這個錯誤。

ClassName.this.runOnUiThread(new Runnable() { 
       public void run() { 
       //Do something on UiThread 

       // enclose your UI manipulated code here in these braces. 
      } 
     });

來源

2016-07-25 13:11:08

無法在靜態上下文中調用動態方法？

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