没有互联网时Windows应用商店应用崩溃

Question

I am creating my first windows store app and i have several web service calls during startup and also periodically through the app. However I have noticed that my app will ot start/crashes or just closes down when I don't have internet access because of the web serivice calls. I want my app to start up in normal way with some initial data and seem normal even when there is no internet access. The data I get from webservice are mostly weather data that I show in various textboxes and graphs.

The code below shows the webservice calls in my extended splash screen.

public sealed partial class ExtendedSplashScreen : Page
{

//parameterItem max1DayAgo = new parameterItem();
//parameterItem min1DayAgo = new parameterItem();


public ExtendedSplashScreen()
{
    this.InitializeComponent();
}

/// <summary>
/// Invoked when this page is about to be displayed in a Frame.
/// </summary>
/// <param name="e">Event data that describes how this page was reached.  The Parameter
/// property is typically used to configure the page.</param>
protected override async void OnNavigatedTo(NavigationEventArgs e)
{

    string[] periodSelector = { "1DayAgo", "1WeekAgo", "1MonthAgo" };
    string[] modeSelector = { "max", "min" };
    string[] parameterSelector = { "umtTemp1", "umtWindSpeed", "umtAdjBaromPress", "umtRainRate" };


    //Create a webservice object
    ServiceReference.WebServiceSoapClient webServiceObj = new ServiceReference.WebServiceSoapClient();
    //First we create an object that holds max data for yesterday
    var getMax1DayAgoObj = await webServiceObj.GetSelectedMaxMinDataAsync(parameterSelector, periodSelector[0], modeSelector[0]);

    //create an object that holds min data for yesterday

    var getMin1DayAgoObj = await webServiceObj.GetSelectedMaxMinDataAsync(parameterSelector, periodSelector[0], modeSelector[1]);
    //Save arrayOfValue and arrayOfUnit to a parameterItem object. these objects are created during startup
    // and the can be accessed and updated by all methods in this page later we will see that maxMinButton_Click method
    //for the maxMinButton will use these data

    //create an object that holds max data for last week
    var getMax1WekAgoObj = await webServiceObj.GetSelectedMaxMinDataAsync(parameterSelector, periodSelector[1], modeSelector[0]);
    //create an object that holds min data for last week
    var getMin1WekAgoObj = await webServiceObj.GetSelectedMaxMinDataAsync(parameterSelector, periodSelector[1], modeSelector[1]);
    //create an object that holds max data for last month
    var getMax1MonthAgoObj = await webServiceObj.GetSelectedMaxMinDataAsync(parameterSelector, periodSelector[2], modeSelector[0]);
    //create an object that holds min data for last month
    var getMin1MonthAgoObj = await webServiceObj.GetSelectedMaxMinDataAsync(parameterSelector, periodSelector[2], modeSelector[1]);


    (App.Current as App).max1DayAgo.arrayOfValue = getMax1DayAgoObj.arrayOfValue;
    (App.Current as App).max1DayAgo.arrayOfUnit = getMax1DayAgoObj.arrayOfUnit;

    (App.Current as App).min1DayAgo.arrayOfValue = getMin1DayAgoObj.arrayOfValue;
    (App.Current as App).min1DayAgo.arrayOfUnit = getMin1DayAgoObj.arrayOfUnit;


    (App.Current as App).max1WeekAgo.arrayOfValue = getMax1WekAgoObj.arrayOfValue;
    (App.Current as App).max1WeekAgo.arrayOfUnit = getMax1WekAgoObj.arrayOfUnit;

    (App.Current as App).min1WeekAgo.arrayOfValue = getMin1WekAgoObj.arrayOfValue;
    (App.Current as App).min1WeekAgo.arrayOfUnit = getMin1WekAgoObj.arrayOfUnit;

    (App.Current as App).max1MonthAgo.arrayOfValue = getMax1MonthAgoObj.arrayOfValue;
    (App.Current as App).max1MonthAgo.arrayOfUnit = getMax1MonthAgoObj.arrayOfUnit;

    (App.Current as App).min1MonthAgo.arrayOfValue = getMin1MonthAgoObj.arrayOfValue;
    (App.Current as App).min1MonthAgo.arrayOfUnit = getMin1MonthAgoObj.arrayOfUnit;


    string[] startupData = new string[13];


    startupData[0] = " " + (App.Current as App).max1DayAgo.arrayOfValue[0] + " " + (App.Current as App).max1DayAgo.arrayOfUnit[0]; //    maxTemp 
    startupData[1] = " " + (App.Current as App).max1DayAgo.arrayOfValue[1] + " " + (App.Current as App).max1DayAgo.arrayOfUnit[1]; //    maxWindSped 
    startupData[2] = " " + (App.Current as App).max1DayAgo.arrayOfValue[2] + " " + (App.Current as App).max1DayAgo.arrayOfUnit[2]; //    maxAirPressure 
    startupData[3] = " " + (App.Current as App).max1DayAgo.arrayOfValue[3] + " " + (App.Current as App).max1DayAgo.arrayOfUnit[3];//     maxRainfall

    startupData[4] = " " + (App.Current as App).min1DayAgo.arrayOfValue[0] + " " + (App.Current as App).min1DayAgo.arrayOfUnit[0]; //    minTemp 
    startupData[5] = " " + (App.Current as App).min1DayAgo.arrayOfValue[1] + " " + (App.Current as App).min1DayAgo.arrayOfUnit[1];//     minWindSped 
    startupData[6] = " " + (App.Current as App).min1DayAgo.arrayOfValue[2] + " " + (App.Current as App).min1DayAgo.arrayOfUnit[2];//     minAirPressure  
    startupData[7] = " " + (App.Current as App).min1DayAgo.arrayOfValue[3] + " " + (App.Current as App).min1DayAgo.arrayOfUnit[3];//     minRainfall



    // Main fields
    // ServiceReference.WebServiceSoapClient webServiceObj = new ServiceReference.WebServiceSoapClient();
    var getLatestTempObj = await webServiceObj.GetLatestDataAsync("umtTemp1");
    var getLatestWindObj = await webServiceObj.GetLatestDataAsync("umtWindSpeed");
    var getLatestwindDirObj = await webServiceObj.GetLatestDataAsync("umtAdjWinDir");
    var getLatestairPressureObj = await webServiceObj.GetLatestDataAsync("umtAdjBaromPress");

    startupData[8] = " " + getLatestTempObj.Value + " " + getLatestTempObj.Unit;//temperatureMainTxtBlock.Text
    startupData[9] = " " + getLatestWindObj.Value + " " + getLatestWindObj.Unit;//temperatureMainTxtBlock.Text

    startupData[10] = "" + getLatestwindDirObj.Value; //temperatureMainTxtBlock.Text

    startupData[11] = " " + getLatestairPressureObj.Value + " " + getLatestairPressureObj.Unit;//temperatureMainTxtBlock.Text

    startupData[12] = "Last update: " + getLatestwindDirObj.Timestamp;//temperatureMainTxtBlock.Text
    //save the startup data to the global variables
    (App.Current as App).NavigateData = startupData;



    this.Frame.SetNavigationState(e.Parameter as string);
    this.Frame.Navigate(typeof(MainPage));
}
}

Answer 1

You need to implement some exception handling around this line: ServiceReference.WebServiceSoapClient webServiceObj = new ServiceReference.WebServiceSoapClient();

and implement a fallback that will work in off-line mode, ie retrieve data from a cache.

Answer 2

You can use NetworkStatusChanged event in App.xaml.cs and then you can declare one static variable and use it to check whether Internet is available or not. If Internet is available do your desired operation otherwise show error message.

public static bool IsInternetAvailable;

void NetworkInformation_NetworkStatusChanged(object sender)
{
    if (NetworkInformation.GetInternetConnectionProfile() != null)
        App.IsInternetAvailable = true;
    else
        App.IsInternetAvailable = false;
}

Always use try catch blocks, when you have probability of exception.

Answer 3

An approach we have in some of our team based apps is prior to any call to return data of the net, the network status is checked. Example:

async Task RefreshFromWeb(...)
{
    if (!App.HasInternetAccess)
    {
        await new Windows.UI.Popups.MessageDialog(Strings.NoInternetWarning).ShowAsync();
        return;
    }

    //attempt access here
}

public static bool HasInternetAccess
{
    get
    {
        var profile = Windows.Networking.Connectivity.NetworkInformation.GetInternetConnectionProfile();
        if (profile == null)
            return false;
        return profile.GetNetworkConnectivityLevel() == 
               Windows.Networking.Connectivity.NetworkConnectivityLevel.InternetAccess;
    }
}

We also took another approach at times which was very similar but uses await and returns true or false (the same could easily be done above, that approach above just gives the dialog)

public static async System.Threading.Tasks.Task HasInternet()
{
    var profile = Windows.Networking.Connectivity.NetworkInformation.GetInternetConnectionProfile();
    var hasNetAccess = profile != null;
    if (!hasNetAccess)
        await new Windows.UI.Popups.MessageDialog(
            content: InfoHub.AppHubViewModel.Strings.NoInternetWarning,
            title: InfoHub.AppHubViewModel.Strings.NoInternetWarning).ShowAsync();
    return hasNetAccess;
}

async void YourControlEvent_Click(object sender, ItemClickEventArgs e)
{
    //if net access, do your stuff, otherwise ignore for now
    if (await IsInternet())
    {
        //do net calls here
    }
}