Android webview canBack（）错误与ActionBarSherlock片段

Question

我正在创建一个带有3个ActionBar选项卡的Web应用程序。每个选项卡都会触发一个webview。在其中一个选项卡上，我需要Android设备后退按钮来触发该webview的goBack操作。我正在尝试一种类似于How to add "Go Back" function in WebView inside Fragment?的blackbelt和netinept建议的解决方案，但是我在MainActivity.java文件中收到以下错误 - “方法canGoBack（）未定义为类型FragmentTab3”。

这是我的代码。请让我知道我可能做错了什么。

--- MainActivity.java ---

在那里我得到 “的方法canGoBack（）是未定义的类型FragmentTab3”

public class MainActivity extends SherlockFragmentActivity { 

    ActionBar.Tab Tab1,Tab2,Tab3; 
    Fragment fragmentTab1 = new FragmentTab1(); 
    Fragment fragmentTab2 = new FragmentTab2(); 
    Fragment fragmentTab3 = new FragmentTab3(); 


    @Override protected void onSaveInstanceState(Bundle outState){ 
     super.onSaveInstanceState(outState); 
     int index = getSupportActionBar().getSelectedNavigationIndex(); 
     outState.putInt("selected_tab_index", index); 
    } 

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

     ActionBar actionBar = getSupportActionBar(); 

     // Hide Actionbar Icon 
     actionBar.setDisplayShowHomeEnabled(false); 

     // Hide Actionbar Title 
     actionBar.setDisplayShowTitleEnabled(false); 

     // Create Actionbar Tabs 
     actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS); 

     // Set Tab Icon and Titles 
     Tab1 = actionBar.newTab().setText("Tab 1"); 
     Tab2 = actionBar.newTab().setText("Tab 2"); 
     Tab3 = actionBar.newTab().setText("Tab 3"); 


     // Set Tab Listeners 
     Tab1.setTabListener(new TabListener(fragmentTab1)); 
     Tab2.setTabListener(new TabListener(fragmentTab2)); 
     Tab3.setTabListener(new TabListener(fragmentTab3)); 

     // Add tabs to actionbar 
     actionBar.addTab(Tab1); 
     actionBar.addTab(Tab2); 
     actionBar.addTab(Tab3); 

     if (savedInstanceState != null) { 
      int index = savedInstanceState.getInt("selected_tab_index", 0); 
      getSupportActionBar().setSelectedNavigationItem(index); 
     } 

    } 

    @Override 
    public void onConfigurationChanged(Configuration newConfig) { 
     super.onConfigurationChanged(newConfig); 
    } 

    @Override 
    public void onBackPressed() { 
      Fragment webview = getSupportFragmentManager().findFragmentById(R.id.webview); 
      if (webview instanceof FragmentTab3) { 
       boolean goback = ((FragmentTab3)webview).canGoBack(); 
       if (!goback) 
        super.onBackPressed(); 
      } 
    }  

} 

--- FragmentTab3.java-- -

public class FragmentTab3 extends SherlockFragment 
{ 

    public WebView webView; 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
      Bundle savedInstanceState) 
    { 
     View rootView = inflater.inflate(R.layout.fragmenttab3, container, false); 

     webView = (WebView) rootView.findViewById(R.id.webview); 
     webView.setBackgroundColor(0); 
     webView.getSettings().setJavaScriptEnabled(true); 
     webView.setWebViewClient(new WebViewClient()); 
     webView.loadUrl("http://www.example.com"); 
     webView.requestFocusFromTouch(); 

     return rootView; 
    } 

} 

--- fragmenttab3.xml ---

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:orientation="vertical" 
    xmlns:tools="http://schemas.android.com/tools" 
    android:layout_width="fill_parent" 
    android:layout_height="fill_parent" > 

    <WebView 
     android:id="@+id/webview" 
     android:tag="webview_tag" 
     android:layout_width="fill_parent" 
     android:layout_height="fill_parent" 
     android:layout_weight="1" /> 

</LinearLayout> 

Answer 1

作为erros说Fragment没有叫做canGoBack的方法。你可以这样做：

public class FragmentTab3 extends SherlockFragment 
{ 
    /// your code 

    public boolean canGoBack() { 
     return webView != null && webView.canGoBack(); 
    } 

} 

Answer 2

这对我在我的MainActivity.java工作我使用4个选项卡每个与Web视图。

@Override 
public void onBackPressed() { 
    // TODO Auto-generated method stub 
    int currPage = mPager.getCurrentItem(); 
    WebView wv = null; 
    switch (currPage) { 
    case 0: 
     wv = (WebView) mPager.getChildAt(currPage).findViewById(R.id.webView1); 
     break; 
    case 1: 
     wv = (WebView) mPager.getChildAt(currPage).findViewById(R.id.webView2); 
     break; 
    case 2: 
     wv = (WebView) mPager.getChildAt(currPage).findViewById(R.id.webView3); 
     break; 
    case 3: 
     wv = (WebView) mPager.getChildAt(currPage).findViewById(R.id.webView4); 
     break; 
    } 

    if (wv != null) { 
     if (wv.canGoBack()) { 
      wv.goBack(); 
     } else { 
      super.onBackPressed(); 
     } 
    } else { 
     super.onBackPressed(); 
    } 
}