Question

I am trying to learn how to call methods throughout a Wpf application.

In a basic experiment, I have two pages, PageData and MainPage.

PageData code:

namespace AppName
{
    public sealed partial class PageData 
    {
        public PageData()
        {
            this.InitializeComponent();
        }

        // works
        private void Button_Click_1(object sender, RoutedEventArgs e)
        {
            mTest();
        }

        public bool mTest()
        {
            var newTbx = new TextBox{
                Text = "Hello",
                FontSize = 50
                };

            Grid.SetRow(newTbx, 3);
            Grid.SetColumn(newTbx, 3);
            gridMainPageData.Children.Add(newTbx);

            return true;
        }
    }
}

MainPage code:

namespace AppName
{
    public sealed class MainPage
    {
        public MainPage()
        {
            InitializeComponent();
        }

        private void pageRoot_Loaded(object sender, RoutedEventArgs e)
        {
             PageData passCall = new PageData();

             mDisplayAlert(passCall.mTest().ToString());
        }
    }
}

It seems that the method mTest() completes because I get the “true” response when MainPage loads (I have a method mDisplayAlert that I use for showing messages on the MainPage UI), but the UI on PageData does not change. I know that mTest() works because the button click event on PageData does work.

Why does the UI not update when called from MainPage?

Answer 1

Because you create a new instance of PageData inside MainPage when what you really want to do is use the same instance to access the exact same controls. When you call the .test() method you create a totally new TextBox and assign data to a totally new Grid when you think you are writing on you first PageData instance.

You have many options from there. You can :

• Pass a reference of the PageData instance to you other form when you create it.
• Create an event between the two classes with a reference to the PageData instance.
• Make your method and controls Static in PageData to make sure the whole program share the same instance. (Not recommanded at all)
• If you want a little work around, you can always set you method to Static and create a Static copy of the control’s instance. Then the compiler will ask for a reference of a Static control and you can assign the instance copy using Controls.Find(yourControl).(Not a good practice either).

Personally i’d use option number 1 but now you know you have the choice.