Android的支持早在网页视图按钮 [英] Android enable back button in webview

问题描述

我用下面的code，以显示我的Andr​​oid应用程序网页视图。

I'm using the following code to display a webview in my Android app.

package com.company.myapp;

import com.google.android.apps.analytics.GoogleAnalyticsTracker;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.Window;
import android.webkit.WebChromeClient;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.Toast;

public class ArticlesActivity extends Activity {

    /** Initialize the Google Analytics Tracker */
    GoogleAnalyticsTracker tracker;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        getWindow().requestFeature(Window.FEATURE_PROGRESS);
        getWindow().setFeatureInt(Window.FEATURE_PROGRESS, Window.PROGRESS_VISIBILITY_ON);
        WebView webview = new WebView(this);
        setContentView(webview); 
        setProgressBarVisibility(true); 
        webview.getSettings().setJavaScriptEnabled(true);
        webview.setScrollBarStyle(View.SCROLLBARS_INSIDE_OVERLAY);
        final Activity activity = this;
        tracker = GoogleAnalyticsTracker.getInstance();
        // Start the tracker, updating google every 20 seconds
        tracker.start((String) getText(R.string.analyticsID), 20, this);

        webview.setWebChromeClient(new WebChromeClient() { 
          public void onProgressChanged(WebView view, int progress) { 
            activity.setProgress(progress * 100 ); 
          } 
        }); 

        webview.setWebViewClient(new WebViewClient() { 
            public void onReceivedError(WebView view, int errorCode, String description, String failingUrl) {
                Toast.makeText(activity, "Oh no! " + description, Toast.LENGTH_SHORT).show();
            }
        });
        webview.loadUrl("http://www.google.com");
    }
    @Override
    public void onResume() {
        tracker.trackPageView("ArticlesActivity");
        super.onResume();
    }
    @Override
    protected void onDestroy() {
      super.onDestroy();
      // Stop the tracker when it is no longer needed.
      tracker.stop();
    }
}

我需要启用后退按钮如果历史存在，而不只是退出的WebView退一步。

I would need to enable the back button to step back if history exists instead of just exiting the webview.

我已经尝试了很多不同的code象这样的例子，但不能得到任何工作。该应用程序刚刚关闭时，后退按钮是pressed。

I've tried many different code examples such as this but can't get any to work. The app just shuts down when the back button is pressed.

下面是我的code与后退按钮code，但它只是崩溃时则后退按钮pressed应用程序：

Here's my code with the back button code but it just crashes the app when then back button is pressed:

package com.company.myapp;

import com.google.android.apps.analytics.GoogleAnalyticsTracker;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.Window;
import android.webkit.WebChromeClient;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.Toast;

public class ArticlesActivity extends Activity {

    WebView webview;

    /** Initialize the Google Analytics Tracker */
    GoogleAnalyticsTracker tracker;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        getWindow().requestFeature(Window.FEATURE_PROGRESS);
        getWindow().setFeatureInt(Window.FEATURE_PROGRESS, Window.PROGRESS_VISIBILITY_ON);
        WebView webview = new WebView(this);
        setContentView(webview); 
        setProgressBarVisibility(true); 
        webview.getSettings().setJavaScriptEnabled(true);
        webview.setScrollBarStyle(View.SCROLLBARS_INSIDE_OVERLAY);
        final Activity activity = this;
        tracker = GoogleAnalyticsTracker.getInstance();
        // Start the tracker, updating google every 20 seconds
        tracker.start((String) getText(R.string.analyticsID), 20, this);

        webview.setWebChromeClient(new WebChromeClient() { 
          public void onProgressChanged(WebView view, int progress) { 
            activity.setProgress(progress * 100 ); 
          } 
        }); 

        webview.setWebViewClient(new WebViewClient() { 
            public void onReceivedError(WebView view, int errorCode, String description, String failingUrl) {
                Toast.makeText(activity, "Oh no! " + description, Toast.LENGTH_SHORT).show();
            }
        });
        webview.loadUrl("http://www.google.com");
    }

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if (keyCode == KeyEvent.KEYCODE_BACK) {

            webview.goBack();

            return true;
        }
        return super.onKeyDown(keyCode, event);
    }

    @Override
    public void onResume() {
        tracker.trackPageView("ArticlesActivity");
        super.onResume();
    }
    @Override
    protected void onDestroy() {
      super.onDestroy();
      // Stop the tracker when it is no longer needed.
      tracker.stop();
    }
}

有人能帮助我解决？

Could someone help me with a solution?

推荐答案

明白了！你在这个线的问题

Got it! Your problem in this line

WebView webview = new WebView(this);

而不是使用您的成员变量要创建内部函数的变量，因此你的成员变量的onkeydown函数内部空。

Instead of using your member variable you are creating a variable inside function, and hence your member variable is null inside onKeyDown function.

只是替换

webview = new WebView(this);

这篇关于Android的支持早在网页视图按钮的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！