java - 在Android WebView上实现后退按钮

Question

我尝试在 android webview 上实现后退按钮，但它说

error: method does not override or implement a method from a supertype    
error: cannot find symbol method onBackPressed()

Activity 代码:

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.graphics.Bitmap;
import android.view.View;
import android.widget.ProgressBar;
import android.view.KeyEvent;

public class MainActivity extends AppCompatActivity {

    String ShowOrHideWebViewInitialUse = "show";
    private WebView webview ;
    private ProgressBar spinner;

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

        webview =(WebView)findViewById(R.id.webView);
        spinner = (ProgressBar)findViewById(R.id.progressBar1);
        webview.setWebViewClient(new CustomWebViewClient());

        webview.getSettings().setJavaScriptEnabled(true);
        webview.getSettings().setDomStorageEnabled(true);
        webview.setOverScrollMode(WebView.OVER_SCROLL_NEVER);
        webview.loadUrl("http://web.com");

    }

    // This allows for a splash screen
    // (and hide elements once the page loads)
    private class CustomWebViewClient extends WebViewClient {

        @Override
        public void onPageStarted(WebView webview, String url, Bitmap favicon) {

            // only make it invisible the FIRST time the app is run
            if (ShowOrHideWebViewInitialUse.equals("show")) {
                webview.setVisibility(webview.INVISIBLE);
            }
        }

        @Override
        public void onPageFinished(WebView view, String url) {

            ShowOrHideWebViewInitialUse = "hide";
            spinner.setVisibility(View.GONE);

            view.setVisibility(webview.VISIBLE);
            super.onPageFinished(view, url);

        }

        @Override
        public void onBackPressed()
        {
            WebView webView = (WebView) findViewById(R.id.webView);
            if(webView.canGoBack()){
                webView.goBack();
            }else{
                super.onBackPressed();
            }
        }
    }
}

我尝试了 stackoverflow 上其他来源的方法，但仍然没有得到有效的答案。也许我的知识还比不上别人。我希望这个社区中的有人可以帮助我解决这个问题。还简要说明了我应该如何使后退按钮在 webview 上工作

Answer 1

在 WebView 外部和 Activity 类方法内部使用 onBackPressed() 方法:

@Override
public void onBackPressed()
        {
            WebView webView = (WebView) findViewById(R.id.webView); // Remove this
            if(webView.canGoBack()){
                webView.goBack();
            }else{
                super.onBackPressed();
            }
      }

}

此外，尝试在 onCreate() 方法中初始化 WebView 并删除 onBackPressed() 中的第二个重复代码。

<小时/>

为了能够在整个Activity中访问它，请像这样初始化它:

public class MainActivity extends AppCompatActivity {

    String ShowOrHideWebViewInitialUse = "show";
    private WebView webview;
    private ProgressBar spinner;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        webview = (WebView) findViewById(R.id.webView); 
}