你的UI没有更新，因为你正在UI线程中运行所有的东西。我猜你需要学习async/await。Here是Stephen Cleary的一个很好的教程。
尝试这段代码，您将看到UI得到了更新。

<Button
    Click="Button_Click"
    Content="Start" />
<TextBlock
    x:Name="MessageTextBlock"
    Text="Click the button." />

private async void Button_Click(object sender, RoutedEventArgs e)
{
    // Starts running on the UI thread.
    MessageTextBlock.Text = "Running process...";
    await RunProcess();
    MessageTextBlock.Text = "Done!";
}

private async Task RunProcess()
{
    // Releases the thread that called this method, 
    // the UI thread in this case, 
    // and lets "another thread" run this "heavy work".
    // This is why the UI thread can update the MessageTextBlock 
    // while "another thread" is doing the "heavy work".
    await Task.Run(async () =>
    {
        // heavy work.
        await Task.Delay(1000);
    });
    // Brings back the UI thread.
}