Wpf – Accessing WPF control validation rules from code

bindingvalidationwpf

XAML:

  <TextBox Name="textboxMin">
      <TextBox.Text>
          <Binding Path="Max">
              <Binding.ValidationRules>
                  <local:IntValidator/>
              </Binding.ValidationRules>
          </Binding>
      </TextBox.Text>
  </TextBox>

Code:

void buttonOK_Click(object sender, RoutedEventArgs e)
{
    // I need to know here whether textboxMin validation is OK
    // textboxMin. ???

    // I need to write something like:
    // if ( textboxMin.Validation.HasErrors )
    //     return;
}

It would be nice also to know, how to disable OK button, if at least one of dialog controls doesn't pass validation – in XAML, using binding. Having this way, I don't need to check validation state in the code.

Best Answer

Validation.HasError is an attached property so you can check it for textboxMin like this

void buttonOK_Click(object sender, RoutedEventArgs e)
{
    if (Validation.GetHasError(textboxMin) == true)
         return;
}

To run all ValidationRules for the TextProperty in code behind you can get the BindingExpression and call UpdateSource

BindingExpression be = textboxMin.GetBindingExpression(TextBox.TextProperty);
be.UpdateSource();

Update

It will take some steps to achieve the binding to disable the button if any validation occurs.

First, make sure all bindings add NotifyOnValidationError="True". Example

<TextBox Name="textboxMin">
    <TextBox.Text>
        <Binding Path="Max" NotifyOnValidationError="True">
            <Binding.ValidationRules>
                <local:IntValidator/>
            </Binding.ValidationRules>
        </Binding>
    </TextBox.Text>
</TextBox>

Then we hook up an EventHandler to the Validation.Error event in the Window.

<Window ...
        Validation.Error="Window_Error">

And in code behind we add and remove the validation errors in an observablecollection as they come and go

public ObservableCollection<ValidationError> ValidationErrors { get; private set; } 
private void Window_Error(object sender, ValidationErrorEventArgs e)
{
    if (e.Action == ValidationErrorEventAction.Added)
    {
        ValidationErrors.Add(e.Error);
    }
    else
    {
        ValidationErrors.Remove(e.Error);
    }
}

And then we can bind IsEnabled of the Button to ValidationErrors.Count like this

<Button ...>
    <Button.Style>
        <Style TargetType="Button">
            <Setter Property="IsEnabled" Value="False"/>
            <Style.Triggers>
                <DataTrigger Binding="{Binding ValidationErrors.Count}" Value="0">
                    <Setter Property="IsEnabled" Value="True"/>
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </Button.Style>
</Button>

Related Solutions

WPF: Create a dialog / prompt

The "responsible" answer would be for me to suggest building a ViewModel for the dialog and use two-way databinding on the TextBox so that the ViewModel had some "ResponseText" property or what not. This is easy enough to do but probably overkill.

The pragmatic answer would be to just give your text box an x:Name so that it becomes a member and expose the text as a property in your code behind class like so:

<!-- Incredibly simplified XAML -->
<Window x:Class="MyDialog">
   <StackPanel>
       <TextBlock Text="Enter some text" />
       <TextBox x:Name="ResponseTextBox" />
       <Button Content="OK" Click="OKButton_Click" />
   </StackPanel>
</Window>

Then in your code behind...

partial class MyDialog : Window {

    public MyDialog() {
        InitializeComponent();
    }

    public string ResponseText {
        get { return ResponseTextBox.Text; }
        set { ResponseTextBox.Text = value; }
    }

    private void OKButton_Click(object sender, System.Windows.RoutedEventArgs e)
    {
        DialogResult = true;
    }
}

Then to use it...

var dialog = new MyDialog();
if (dialog.ShowDialog() == true) {
    MessageBox.Show("You said: " + dialog.ResponseText);
}

Wpf – validation – how to show tooltips and disable “run” button

To show the error message in a tool tip put this into your Application.Resources:

<Style x:Key="textBoxInError" TargetType="{x:Type TextBox}">
  <Style.Triggers>
    <Trigger Property="Validation.HasError" Value="true">
      <Setter Property="ToolTip"
        Value="{Binding RelativeSource={x:Static RelativeSource.Self},
                        Path=(Validation.Errors)[0].ErrorContent}"/>
    </Trigger>
  </Style.Triggers>
</Style>

( Example from http://msdn.microsoft.com/en-us/library/system.windows.controls.validation.errortemplate.aspx )

To enable/disable a button you could use something along the line of

<Button x:Name="btnOK" Content="OK" IsDefault="True" Click="btnOK_Click">
  <Button.Style>
    <Style TargetType="{x:Type Button}">
      <Setter Property="IsEnabled" Value="false" />
      <Style.Triggers>
        <MultiDataTrigger>
          <MultiDataTrigger.Conditions>
            <Condition Binding="{Binding ElementName=txt1, Path=(Validation.HasError)}" Value="false" />
            <Condition Binding="{Binding ElementName=txt2, Path=(Validation.HasError)}" Value="false" />
          </MultiDataTrigger.Conditions>
          <Setter Property="IsEnabled" Value="true" />
        </MultiDataTrigger>
      </Style.Triggers>
    </Style>
  </Button.Style>
</Button>

or you could implement ICommand and use command binding.

EDIT

Here is a fully working example. It displays a window with two TextBoxes. The Button is enabled if and only if both TextBoxes are non-empty. Create a project called ValidationDemo and put the following files in it:

MainWindow.xaml:

<Window x:Class="ValidationDemo.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="146" Width="223">
  <Window.Resources>
    <Style TargetType="{x:Type TextBox}">
      <Style.Triggers>
        <Trigger Property="Validation.HasError" Value="true">
          <Setter Property="ToolTip" Value="{Binding RelativeSource={x:Static RelativeSource.Self}, Path=(Validation.Errors)[0].ErrorContent}"/>
        </Trigger>
      </Style.Triggers>
    </Style>
  </Window.Resources>
  <Grid>
    <Label Content="A" Height="28" HorizontalAlignment="Left" Margin="46,7,0,0" Name="label1" VerticalAlignment="Top" />
    <TextBox Name="txtA" Text="{Binding Path=TextA, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True, ValidatesOnExceptions=True}" Height="23" HorizontalAlignment="Left" Margin="69,12,0,0" VerticalAlignment="Top" Width="120" />
    <Label Content="B" Height="28" HorizontalAlignment="Left" Margin="46,39,0,0" Name="label2" VerticalAlignment="Top" />
    <TextBox Name="txtB" Text="{Binding Path=TextB, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True, ValidatesOnExceptions=True}" Height="23" HorizontalAlignment="Left" Margin="69,41,0,0" VerticalAlignment="Top" Width="120" />
    <Button Name="btnOk" Content="OK" Height="23" HorizontalAlignment="Left" Margin="114,70,0,0" VerticalAlignment="Top" Width="75" Click="btnOk_Click">
      <Button.Style>
        <Style TargetType="{x:Type Button}">
          <Setter Property="IsEnabled" Value="false" />
          <Style.Triggers>
            <MultiDataTrigger>
              <MultiDataTrigger.Conditions>
                <Condition Binding="{Binding ElementName=txtA, Path=(Validation.HasError)}" Value="false" />
                <Condition Binding="{Binding ElementName=txtB, Path=(Validation.HasError)}" Value="false" />
              </MultiDataTrigger.Conditions>
              <Setter Property="IsEnabled" Value="true" />
            </MultiDataTrigger>
          </Style.Triggers>
        </Style>
      </Button.Style>
    </Button>
  </Grid>
</Window>

MainWindow.xaml.cs:

using System.Windows;

namespace ValidationDemo
{
  /// <summary>
  /// Interaction logic for MainWindow.xaml
  /// </summary>
  public partial class MainWindow : Window
  {

    private Model model = new Model();

    public MainWindow()
    {
      InitializeComponent();
      this.DataContext = this.model;
    }

    private void btnOk_Click(object sender, RoutedEventArgs e)
    {
      Application.Current.Shutdown();
    }
  }
}

Model.cs:

using System;
using System.ComponentModel;

namespace ValidationDemo
{
  public class Model : INotifyPropertyChanged, IDataErrorInfo
  {
    public event PropertyChangedEventHandler PropertyChanged;

    private string textA = string.Empty;
    public string TextA
    {
      get
      {
        return this.textA;
      }
      set
      {
        if (this.textA != value)
        {
          this.textA = value;
          this.OnPropertyChanged("TextA");
        }
      }
    }

    private string textB = string.Empty;
    public string TextB
    {
      get
      {
        return this.textB;
      }
      set
      {
        if (this.textB != value)
        {
          this.textB = value;
          this.OnPropertyChanged("TextB");
        }
      }
    }

    public string Error
    {
      get { throw new NotImplementedException(); }
    }

    public string this[string columnName]
    {
      get
      {
        string result = string.Empty;
        switch (columnName)
        {
          case "TextA":
            if (string.IsNullOrEmpty(this.textA))
            {
              result = "'A' must not be empty";
            }
            break;
          case "TextB":
            if (string.IsNullOrEmpty(this.textA))
            {
              result = "'B' must not be empty";
            }
            break;
        }
        return result;
      }
    }

    protected virtual void OnPropertyChanged(string propertyName)
    {
      if (this.PropertyChanged != null)
      {
        this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
      }
    }

  }

}

Best Answer

Related Solutions

WPF: Create a dialog / prompt

Wpf – validation – how to show tooltips and disable “run” button

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