如果设备处于脱机状态，则片段 Web 视图中会出现警报弹出窗口

Question

如果设备处于脱机状态，我想在片段 Web 视图中显示警报弹出窗口，而不是显示默认消息（"网页....."）。我是安卓应用程序开发领域的新手。我已经添加了进度条，但我不知道在哪里以及在哪里包含 toast 代码以提醒消息。这是我的标签信息.java

选项卡信息.java

public class tabinfo extends Fragment{
    public WebView mwebView;
    ProgressBar bar;
    public tabinfo(){
    }
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View rootView = inflater.inflate(R.layout.tabinfo, null);
        bar = (ProgressBar) rootView.findViewById(R.id.progressBar2);
        // initialize bar
        mwebView = (WebView) rootView.findViewById(R.id.webview);
        mwebView.loadUrl("https://mbasic.facebook.com");
        mwebView.getSettings().setJavaScriptEnabled(true);
        mwebView.setWebViewClient(new MyWebViewClient());
        return rootView;
    }
    private class MyWebViewClient extends WebViewClient {
        @SuppressWarnings("deprecation")
        @Override
        public boolean shouldOverrideUrlLoading(WebView view, String url) {
            view.loadUrl(url);
            return true;
        }
        @Override
        public void onPageStarted(final WebView view, final String url, final Bitmap favicon) {
            bar.setVisibility(View.VISIBLE);
            // ^^^ use it as it is
            super.onPageStarted(view, url, favicon);
        }
        @Override
        public void onPageFinished(WebView view, String url) {
            bar.setVisibility(View.GONE);
            // ^^^ use it as it is
            super.onPageFinished(view, url);
        }
    }
}

Answer 1

in MyWebViewClient class Override onReceivedError 方法

@Override
public void onReceivedError(WebView view, int errorCode, String description, 
String failingUrl) {
super.onReceivedError(view, errorCode, description, failingUrl);
view.loadUrl("about:blank");
ConnectivityManager cm = (ConnectivityManager) 
getSystemService(Context.CONNECTIVITY_SERVICE);
if(cm.getActiveNetworkInfo() != null){
 Toast toast = Toast.makeText(context, " Internet Connected", Toast.LENGTH_LONG).show();
}
else
Toast toast = Toast.makeText(MainActivity.this, "No Internet Connection", Toast.LENGTH_LONG).show;
}

在清单中，

<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

在片段中获取上下文

Context context;
@Override
public void onAttach(Context context) {
super.onAttach(context);
 this.context = context;
}