佈局與Web視圖上的按鈕

Question

我不明白爲什麼這2個按鈕不起作用，我有一個佈局文件，當用戶在我的應用程序中選擇某個主題時創建。有了它的佈局，它有一個webview它有2個按鈕goback和goforward。

<Button 
    android:id="@+id/button1" 
    android:layout_width="wrap_content" 
    android:text="Back" 
    android:layout_alignParentLeft="true" 
    android:layout_height="wrap_content" 
    android:background="@drawable/button_blue" 
    style="@style/ButtonText"> 
    </Button> 

    <Button 
    android:id="@+id/button2" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignParentRight="true" 
    android:background="@drawable/button_blue" 
    style="@style/ButtonText" 
    android:text="Forward"> 
</Button> 


    <WebView 
    android:id="@+id/webview01" 
    android:layout_width="fill_parent" 
    android:layout_height="0dp" 
    android:layout_weight="1.12" > 

這是不是整個佈局文件，但這裏的東西，我跟在web視圖工作位和2個按鈕，現在我的主要活動中，這裏是我按鈕的代碼。具有

 @Override 
public void onCreate(Bundle savedInstanceState) { 

    super.onCreate(savedInstanceState); 

    if (Prefs.theme.equals("Theme1")) 
     setContentView(R.layout.main); 
    else if (Prefs.theme.equals("Theme2")) 
     setContentView(R.layout.main2); 
    else if (Prefs.theme.equals("Theme3")) 
     setContentView(R.layout.main3); 
    else setContentView(R.layout.main); 



    btnForward=(Button) findViewById (R.id.button1); 
    btnBackward=(Button) findViewById (R.id.button2); 
    btnForward.setOnClickListener(this); 
    btnBackward.setOnClickListener(this); 


    // more code within on create ..... 

// Later in the code 

public void onClick(View v) { 

    switch(v.getId()) { 

     case R.id.button1: 
      WebViewClientDemoActivity.web.goBack(); 
      break; 

     case R.id.button2: 
      WebViewClientDemoActivity.web.goForward(); 
      break; 
    } 

//

我問題IM是默認它加載main.xml中不main3（這是爲2個按鈕是）

logcat的錯誤

07-27 16:00:34.802: E/AndroidRuntime(547): FATAL EXCEPTION: main 
    07-27 16:00:34.802: E/AndroidRuntime(547): java.lang.RuntimeException: Unable to start activity  ComponentInfo{com.jaisonbrooks.enlighten/com.jaisonbrooks.enlighten.WebViewClientDemoActivity}: java.lang.NullPointerException 
    07-27 16:00:34.802: E/AndroidRuntime(547): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647) 
    07-27 16:00:34.802: E/AndroidRuntime(547): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663) 
    07-27 16:00:34.802: E/AndroidRuntime(547): at android.app.ActivityThread.access$1500(ActivityThread.java:117) 
    07-27 16:00:34.802: E/AndroidRuntime(547): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931) 
    07-27 16:00:34.802: E/AndroidRuntime(547): at android.os.Handler.dispatchMessage(Handler.java:99) 
    07-27 16:00:34.802: E/AndroidRuntime(547): at android.os.Looper.loop(Looper.java:123) 
    07-27 16:00:34.802: E/AndroidRuntime(547): at android.app.ActivityThread.main(ActivityThread.java:3683) 
    07-27 16:00:34.802: E/AndroidRuntime(547): at java.lang.reflect.Method.invokeNative(Native Method) 
    07-27 16:00:34.802: E/AndroidRuntime(547): at java.lang.reflect.Method.invoke(Method.java:507) 
    07-27 16:00:34.802: E/AndroidRuntime(547): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 
    07-27 16:00:34.802: E/AndroidRuntime(547): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 
    07-27 16:00:34.802: E/AndroidRuntime(547): at dalvik.system.NativeStart.main(Native Method) 
    07-27 16:00:34.802: E/AndroidRuntime(547): Caused by: java.lang.NullPointerException 
    07-27 16:00:34.802: E/AndroidRuntime(547): at com.jaisonbrooks.enlighten.WebViewClientDemoActivity.onCreate(WebViewClientDemoActivity.java:75) 
    07-27 16:00:34.802: E/AndroidRuntime(547): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
    07-27 16:00:34.802: E/AndroidRuntime(547): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611) 
    07-27 16:00:34.802: E/AndroidRuntime(547): ... 11 more 

Answer 1

首先在onCreate方法通過IDS發現你的按鈕：

public class YourActivity extends Activity implements OnClickListener { 
Button btnForward; 
Button btnBackward; 

@Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.main); 

     btnForward=(Button) findViewById (R.id.btnForward); 
     btnBackward=(Button) findViewById (R.id.btnBackward); 

     //set listeners 
     btnForward.setOnClickListener(this); 
     btnBackward.setOnClickListener(this); 

     // your code here .... 
    } 

@Override 
public void onClick(View v) { 
    switch(v.getId()) { 

     case R.id.btnBackward: 
      WebViewClientDemoActivity.web.goBack(); 
      break; 
     case R.id.btnForward: 
      WebViewClientDemoActivity.web.goForward(); 
      break; 
    } 
} 

}

Answer 2

<Button 
android:id="@+id/button1" 
android:layout_width="wrap_content" 
android:text="Back" 
android:layout_alignParentLeft="true" 
android:layout_height="wrap_content" 
android:background="@drawable/button_blue" 
style="@style/ButtonText" /> 

<Button 
android:id="@+id/button2" 
android:layout_width="wrap_content" 
android:layout_height="wrap_content" 
android:layout_alignParentRight="true" 
android:background="@drawable/button_blue" 
style="@style/ButtonText" 
android:text="Forward" /> 

試試這個。

後來在Java代碼中，這樣做

Button btnNext = (Button) findViewById(R.id.button2); 
btnNext.setOnClickListener(new OnClickListener() 
{ 
     @Override 
    public void onClick(View v) 
    { 
     WebViewClientDemoActivity.web.goForward(); 
    } 
}); 


Button btnBack = (Button) findViewById(R.id.button1); 
btnNext.setOnClickListener(new OnClickListener() 
{ 
     @Override 
    public void onClick(View v) 
    { 
     WebViewClientDemoActivity.web.goBack(); 
    } 
}); 

Answer 3

它應該工作。確保你沒有相同的兩個按鈕@id。
這是一個常見的問題，當你從一個乘你的按鈕。 （複製/粘貼）