goBack()在按下后退按钮时使我的应用程序强制关闭

Question

我试图让Android设备的后退按钮成为一种在WebView中向后导航的方式.但是,当我单击后退按钮时,它会强制关闭.

这是我的.java文件(已编辑的包名称):

package ----;

import android.app.Activity;
import android.os.Bundle;
import android.view.KeyEvent;
import android.view.View;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;

public class ---- extends Activity {
WebView mainWebView;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

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

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

    mainWebView.setWebViewClient(new MyCustomWebViewClient());
    mainWebView.setScrollBarStyle(View.SCROLLBARS_INSIDE_OVERLAY);

    mainWebView.loadUrl("https://app.tent.is/global");
}

@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) && mainWebView.canGoBack()) {
        mainWebView.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);
}

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

Answer 1

这里

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

改变

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

事物是WebView mainWebView;您之前声明的对象onCreate,它永远不会被初始化.