要检查网络连接可用性，请使用以下命令
public class CheckNetwork {
private static final String TAG = CheckNetwork.class.getSimpleName();
public static boolean isInternetAvailable(Context context)
{
NetworkInfo info = (NetworkInfo) ((ConnectivityManager)
context.getSystemService(Context.CONNECTIVITY_SERVICE)).getActiveNetworkInfo();
if (info == null)
{
Log.d(TAG,"no internet connection");
return false;
}
else
{
if(info.isConnected())
{
Log.d(TAG," internet connection available...");
return true;
}
else
{
Log.d(TAG," internet connection");
return true;
}
}
}
}
在您的活动中
if(CheckNetwork.isInternetAvailable(Activity.this)) //returns true if internet available
{
//do something. loadwebview.
}
else
{
Toast.makeText(Activity.this,"No Internet Connection",1000).show();
}
按下后退按钮
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if(event.getAction() == KeyEvent.ACTION_DOWN){
switch(keyCode)
{
case KeyEvent.KEYCODE_BACK:
if(mWebView.canGoBack() == true){
mWebView.goBack();
}else{
finish();
}
return true;
}
}
return super.onKeyDown(keyCode, event);
}
更新：如果您需要始终检查网络连接可用性，系统会在连接发生变化或连接丢失时广播事件。您可以通过注册广播来捕获活动中的这些广播。但不需要的时候需要注销。
下面的链接中有一个示例。
检查互联网连接的 Android 服务？.
或者您可以使用在后台检查互联网连接的服务。但不需要的时候需要销毁该服务。但服务用于在后台运行长时间运行的操作
更新2：
尝试下面的方法。我已经测试过。它适用于我的三星 Galaxy S3。
在清单中添加这些权限
<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE"/>
你的activity_main.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity" >
<WebView
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_centerHorizontal="true"
android:layout_centerVertical="true"
android:id="@+id/wv"/>
</RelativeLayout>
您的活动
public class MainActivity extends Activity {
private WebView webView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
webView = (WebView) findViewById(R.id.wv);
if(CheckNetwork.isInternetAvailable(MainActivity.this))
{
CookieManager cookieManager = CookieManager.getInstance();
cookieManager.setAcceptCookie(true);
// webView = (WebView) findViewById(R.id.wv);
// webView.setWebViewClient(new MyWebViewClient());
webView.getSettings().setJavaScriptEnabled(true);
webView.setWebChromeClient(new WebChromeClient() {
public void onProgressChanged(WebView view, int progress) {
// Activities and WebViews measure progress with different scales.
// The progress meter will automatically disappear when we reach 100%
MainActivity.this.setProgress(progress * 1000);
}
});
webView.setWebViewClient(new WebViewClient() {
public void onReceivedError(WebView view, int errorCode, String description, String failingUrl) {
Toast.makeText(MainActivity.this, "Oh no! " + description, Toast.LENGTH_SHORT).show();
}
});
webView.loadUrl("http://slashdot.org/");
}
else{
//no connection
Toast toast = Toast.makeText(MainActivity.this, "No Internet Connection", Toast.LENGTH_LONG);
toast.show();
}
}
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if ((keyCode == KeyEvent.KEYCODE_BACK) && webView.canGoBack()) {
webView.goBack();
return true;
}
else
{
finish();
}
return super.onKeyDown(keyCode, event);
}
}
