Question

在我的webview应用程序中，我打开了一个网站，用于在横向中显示lways。我还添加了onKeyDown函数（）。但是当打开链接并按下后退键时，应用程序将关闭。请帮助我解决

WebActivity.java

package com.example.samworkshops;



import android.app.Activity;
import android.content.pm.ActivityInfo;
import android.os.Bundle;
import android.view.KeyEvent;
import android.webkit.WebView;
import android.webkit.WebViewClient;

public class WebActivity extends Activity {
    public WebView webview;


    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        WebView webview = (WebView) findViewById(R.id.webview);
        webview.setWebViewClient(new WebViewClient());
        setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);
        webview.getSettings().setJavaScriptEnabled(true);
        webview.getSettings().setUseWideViewPort(true);
        webview.getSettings().setLoadWithOverviewMode(true);
        webview.loadUrl("http://app.samworkshops.org");

    }
    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        // Check if the key event was the Back button and if there's history
        if ((keyCode == KeyEvent.KEYCODE_BACK) && webview.canGoBack()) {
            webview.goBack();
            return true;
        }
        // If it wasn't the Back key or there's no web page history, bubble up to the default
        // system behavior (probably exit the activity)
        return super.onKeyDown(keyCode, event);
    }
}

Answer 1

更改

 WebView webview = (WebView) findViewById(R.id.webview);
 // declared again and initialized. becomes local to onCreate

到

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

因为你已经拥有

 public class WebActivity extends Activity {
 public WebView webview; // declared but this is never initialized

我猜它是导致崩溃的NullPointerException

Answer 2

可能在调用onKeyDown

之前调用onBackPressed（）方法

这样做。删除onKeyDown并将其放入：

@Override
    public void onBackPressed() {
        if (webview.canGoBack()) {
                      webview.goBack();
                      return;
                  }
        super.onBackPressed();
    }

Answer 3

您有两次声明WebView

试试这个：

替换此WebView webview = (WebView) findViewById(R.id.webview); 由

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

并且也这样做

@Override
    public void onBackPressed() {
       webview.goBack();

    }

在你添加onBackPressed（）方法之前请注释onKeyDown方法

按下后退键时，webview app force关闭

3 个答案: