UWP等待Textbox.Textchanged事件触发

Question

How to change the text in a UWP Textbox and wait for it's TextChanged to complete before moving on, or not fire the TextChanged event at all.

The scenario. Main UI shows a red flag if the TextBox text changes - however, I need to reset it occasionally (TextBox.Text = "", or some other text), when that happens, I want my red flag to go green.

Expected process flow

TextBox.Text = ""
TextBox.Changed event fires - causing my flag to go red
Reset flag to green

Actual process flow

TextBox.Text = ""
Reset flag to green
TextBox.Changed event fires - causing my flag to go red

What I think is happening Setting the TextBox.Text causes an event to be added to dispatch queue, which doesn't fire until the UI thread is idle, this means the next command (Reset flag to green) happens before the TextChanged event is consumed. It's also possible that the event is waiting for the TextBox to finish rendering before firing the event, but I can't be certain.

Solution? Any help appreciated.

Answer 1

答案很简单：使用布尔标志来区分何时触发“红色标志”和何时触发绿色标志。

Answer 2

In "real life", I would be creating a custom control based on a textbox and defining all of the states in Blend and probably add a dirty state or something and drive it all via a boolean property. However, here some proof of concept code that seems to do what I gather you need. I think the only real difference to what you have been trying is that I am tracking the "old value" and comparing it when the text changes to determine its cleanliness. The magic reset also controls that old value.

control code:

namespace DirtyTextBox
{
    public class DirtyNotifyingTextBox : TextBox
    {
        public DirtyNotifyingTextBox()
        {
            this.DefaultStyleKey = typeof(TextBox);
            DataContextChanged += DirtyNotifyingTextBox_DataContextChanged;
        }

        private void DirtyNotifyingTextBox_DataContextChanged(Windows.UI.Xaml.FrameworkElement sender, Windows.UI.Xaml.DataContextChangedEventArgs args)
        {
            _originalValue = this.Text;
            TextChanged += DirtyNotifyingTextBox_TextChanged;
            SetToGreen();
        }

        private string _originalValue { get; set; }

        private void DirtyNotifyingTextBox_TextChanged(object sender, TextChangedEventArgs e)
        {
            if (this.Text != _originalValue)
            {
                SetToRed();
            }
            else
            {
                SetToGreen();
            }
        }

        private void SetToGreen()
        {
            this.BorderBrush = new SolidColorBrush(Windows.UI.Color.FromArgb(255, 50, 205, 0));
        }

        private void SetToRed()
        {
            this.BorderBrush = new SolidColorBrush(Windows.UI.Color.FromArgb(255, 255, 0, 0));
        }

        public void Reset()
        {
            Reset(string.Empty);
        }

        public void Reset(string resetValue)
        {
            _originalValue = resetValue;
            this.Text = resetValue;
        }

        protected override void OnApplyTemplate()
        {
            base.OnApplyTemplate();
        }
    }
}

sample usage:

<StackPanel Orientation="Horizontal">
    <local:DirtyNotifyingTextBox x:Name="dtextbox" Width="250" Height="50" />
    <Button Content="reset" Click="Reset" Margin="10 0" />
    <Button Content="reset with value" Click="ResetWithValue" Margin="10 0" />
    <Button Content="change text with code" Click="UpdateText" Margin="10 0" />
</StackPanel>

code behind:

private void Reset(object sender, RoutedEventArgs e)
{
    dtextbox.Reset();
}

private void ResetWithValue(object sender, RoutedEventArgs e)
{
    dtextbox.Reset("Magic Reset");
}

private void UpdateText(object sender, RoutedEventArgs e)
{
    dtextbox.Text = "updated text";
}