更改主题后更改背景图像

Question

I'm trying to change the ImageSource of an ImageBrush when the user changes the theme of his phone in his settings.

So currently I have this:

XAML:

<ImageBrush ImageSource="{Binding ImageSource, Mode=OneTime}" Stretch="UniformToFill"/>

CodeBehind:

public string ImageSource
{
    get
    {
        if ((Visibility)App.Current.Resources["PhoneDarkThemeVisibility"]
            == Visibility.Visible)
        {
            return "/Images/BGDark.png";

        }
        else
        {
            return "/Images/BG.png";

        }
    }
    private set { }
}

As you can see, I'm setting the Background when the application has been started. The app will set the Background by seeing which Theme has been selected.

My problem is now that when the user goes to settings (application hasn't been closed!) and changes the theme, the Background/ImageSource won't be updated, when he activates the app pagain. I've thought that maybe I could change it by setting the new Background here:

App.xaml.cs:

private void Application_Activated(object sender, ActivatedEventArgs e)
{
    //access somehow the CodeBehind of my MainPage and change the ImageSource
}

But I don't know how I would access the property... Is there maybe another solution to change the background while the app is still running and the user changes the theme?

Answer 1

You can try to put the logic in Page.OnNavigatedTo() instead of Application_Activated() :

protected override void OnNavigatedTo(NavigationEventArgs e)
{
    //do some logic to check if changing Background is necessary
    //if it is then change the Background, else simply return;
}

Answer 2

try this:

Model class:

class SampleClass
{
    public string ImageSource
    {
        get
        {
            if ((Visibility)App.Current.Resources["PhoneDarkThemeVisibility"] == Visibility.Visible)
            {
                return "Dark";//You can set your Image here

            }
            else
            {
                return "Light";//You can set your Image here

            }
        }
        private set { }
    }
}

Usage :

private void Application_Activated(object sender, ActivatedEventArgs e)
{
    SampleClass obj = new SampleClass();
    Debug.WriteLine(obj.ImageSource);
}

NOTE :

You are needed to mark tombstone upon deactivation while debugging as shown in Image. After doing it it would work as you are suppose to do