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copied!<p>To show the error message in a tool tip put this into your Application.Resources:</p> <pre><code><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> </code></pre> <p>( Example from <a href="http://msdn.microsoft.com/en-us/library/system.windows.controls.validation.errortemplate.aspx" rel="noreferrer">http://msdn.microsoft.com/en-us/library/system.windows.controls.validation.errortemplate.aspx</a> )</p> <p>To enable/disable a button you could use something along the line of</p> <pre><code><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> </code></pre> <p>or you could implement ICommand and use command binding.</p> <p><strong>EDIT</strong></p> <p>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:</p> <p><strong>MainWindow.xaml:</strong></p> <pre><code><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> </code></pre> <p><strong>MainWindow.xaml.cs:</strong></p> <pre><code>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(); } } } </code></pre> <p><strong>Model.cs:</strong></p> <pre><code>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)); } } } } </code></pre>

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