How to forbid the Back button function in a page of windows phone 8.1 app?

Question

I do not want the user presses Back Button to back to the previous page while the data syncing is in progress.

I have tried the following code, but it does not work:

        public SettingPage()
        {
            this.InitializeComponent();

            this.navigationHelper = new NavigationHelper(this);
            this.navigationHelper.LoadState += this.NavigationHelper_LoadState;
            this.navigationHelper.SaveState += this.NavigationHelper_SaveState;
            Windows.Phone.UI.Input.HardwareButtons.BackPressed += HardwareButtons_BackPressed;
        }

        private void HardwareButtons_BackPressed(object sender, Windows.Phone.UI.Input.BackPressedEventArgs e)
        {
            if (this.isSyncing)
            {
                e.Handled = true;
            }
        }

Answer 1

Have you check isSyncing are true?

This code is right, but you need to check and using debug point to check, wether e.Handled is executed.

Answer 2

Because the NavigationHelper will process this event first. you need to modify this behavior.

you can see the code in NavigationHelper.cs (it's constructor)

       public NavigationHelper(Page page)
        {
            this.Page = page;

            // When this page is part of the visual tree make two changes:
            // 1) Map application view state to visual state for the page
            // 2) Handle hardware navigation requests
            this.Page.Loaded += (sender, e) =>
            {
#if WINDOWS_PHONE_APP
                Windows.Phone.UI.Input.HardwareButtons.BackPressed += HardwareButtons_BackPressed;
#else

#if WINDOWS_PHONE_APP
        /// <summary>
        /// Invoked when the hardware back button is pressed. For Windows Phone only.
        /// </summary>
        /// <param name="sender">Instance that triggered the event.</param>
        /// <param name="e">Event data describing the conditions that led to the event.</param>
        private void HardwareButtons_BackPressed(object sender, Windows.Phone.UI.Input.BackPressedEventArgs e)
        {
            if (this.GoBackCommand.CanExecute(null))
            {
                e.Handled = true;
                this.GoBackCommand.Execute(null);
            }
        }

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