基本的webview应用程序问题

Question

我想做一个基本的webview应用程序，但它给4错误。

Error:(35, 9) error: method does not override or implement a method from a supertype

Error:(46, 32) error: non-static method canGoBack() cannot be referenced from a static context

Error:(47, 32) error: non-static method goBack() cannot be referenced from a static context

Error:Execution failed for task ':app:compileDebugJava'. Compilation failed; see the compiler error output for details.

谁能告诉我我的代码有什么问题吗？

这里是我的代码：

import android.support.v7.app.ActionBarActivity; 
import android.os.Bundle; 
import android.view.KeyEvent; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.Window; 
import android.view.WindowManager; 
import android.webkit.WebSettings; 
import android.webkit.WebView; 
import android.webkit.WebViewClient; 


public class MainActivity extends ActionBarActivity { 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     requestWindowFeature(Window.FEATURE_NO_TITLE); 
     getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, 
       WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN); 
     setContentView(R.layout.activity_main); 

     WebView mainWebView = (WebView) findViewById(R.id.mainWebView); 

     WebSettings webSettings = mainWebView.getSettings(); 
     webSettings.setJavaScriptEnabled(true); 

     mainWebView.setWebViewClient(new MyCustomWebViewClient()); 
     mainWebView.loadUrl("http://facebook.com/"); 
    } 

    private class MyCustomWebViewClient extends WebViewClient { 
     @Override 
     public boolean shouldOverrideLoading(WebView view, String url) { 
      view.loadUrl(url); 
      return true; 
     } 
    } 

    public boolean onKeyDown(int keyCode, KeyEvent event) { 
     if (event.getAction() == KeyEvent.ACTION_DOWN) { 
      switch (keyCode) { 
       case KeyEvent.KEYCODE_BACK: 
        if (WebView.canGoBack()) { 
         WebView.goBack(); 
        } else { 
         finish(); 
        } 
        return true; 
      } 
     } 
    } 
} 

这是我的新代码现在在你们的帮助，显示没有错误，但仍然无法正常工作（无法完成gradle这个执行，当我尝试在运行它仿真器）：

public class MainActivity extends ActionBarActivity { 
    private WebView mainWebView; 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     requestWindowFeature(Window.FEATURE_NO_TITLE); 
     getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, 
       WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN); 
     setContentView(R.layout.activity_main); 

     mainWebView = (WebView) findViewById(R.id.mainWebView); 

     WebSettings webSettings = mainWebView.getSettings(); 
     webSettings.setJavaScriptEnabled(true); 

     mainWebView.setWebViewClient(new MyCustomWebViewClient()); 
     mainWebView.loadUrl("http://facebook.com/"); 
    } 

    private class MyCustomWebViewClient extends WebViewClient { 

     public boolean shouldOvrrideLoading (WebView view, String url) { 
      view.loadUrl(url); 
      return true; 
     } 
    } 

    public boolean onKeyDown(int keyCode, KeyEvent event) { 
     if (event.getAction() == KeyEvent.ACTION_DOWN) { 
      switch (keyCode) { 
       case KeyEvent.KEYCODE_BACK: 
        if (mainWebView.canGoBack()) { 
         mainWebView.goBack(); 
        } else { 
         finish(); 
        } 
        return true; 
      } 
     } 
     return false; 
    } 
} 

Answer 1

错误实际上解释了什么是错的：

“非静态方法GoBack的（）不能从静态上下文中引用“

你需要与你的实例化的web视图，以取代静态WebView.canGoBack()mainWebView.canGoBack()

这同样适用于WebView.goBack()

Answer 2

mainWebView变量应该是类MainActivity的对象

public class MainActivity extends ActionBarActivity { 
     private WebView mainWebView; 
     @Override 
     protected void onCreate(Bundle savedInstanceState) { 
      super.onCreate(savedInstanceState); 
      requestWindowFeature(Window.FEATURE_NO_TITLE); 
      getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, 
        WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN); 
      setContentView(R.layout.activity_main); 

      mainWebView = (WebView) findViewById(R.id.mainWebView); 

      WebSettings webSettings = mainWebView.getSettings(); 
      webSettings.setJavaScriptEnabled(true); 

      mainWebView.setWebViewClient(new MyCustomWebViewClient()); 
      mainWebView.loadUrl("http://facebook.com/"); 
     } 

     private class MyCustomWebViewClient extends WebViewClient { 
      @Override 
      public boolean shouldOverrideLoading(WebView view, String url) { 
       view.loadUrl(url); 
       return true; 
      } 
     } 

     public boolean onKeyDown(int keyCode, KeyEvent event) { 
      if (event.getAction() == KeyEvent.ACTION_DOWN) { 
       switch (keyCode) { 
        case KeyEvent.KEYCODE_BACK: 
         if (mainWebView.canGoBack()) { 
          mainWebView.goBack(); 
         } else { 
          finish(); 
         } 
         return true; 
       } 
      } 
     } 
    }