Using validation rules to disable a button

Question

Hi,
I know that in WPF, I could bind a button's IsEnabled property with some TextBox to receive the Validation.HasError result as its IsEnabled value. This does work for simple TextBox.

But in my case, I have a DataGrid for user to do the input. And for the TextBox column of the DataGrid, I binding a validation rule to it as followings:

The validation works fine in this case(When the input is incorrect, the TextBox cell is shown with a red border). However, the button I want to disable is totally lost control. Even if the input is incorrect, I can still click the button.
Below is the trigger code for disabling the button

So, anyone can tell me how could I do this in the situation. Thanks a lot.

Accepted Answer

Hi,
you can use data object with INotifyPropertyChanged to inform about changes and IDataErrorInfo for detection of errors in data objects. Inheriting Collection from ObservableCollection you can inform the UI about changes and switch enable / disable of command button using RelayCommand class.

Try following demo:

XAML:

And classes:

using System;  
using System.Collections.Generic;  
using System.Collections.ObjectModel;  
using System.Collections.Specialized;  
using System.ComponentModel;  
using System.Globalization;  
using System.Runtime.CompilerServices;  
using System.Windows;  
using System.Windows.Controls;  
using System.Windows.Data;  
using System.Windows.Input;  

namespace WpfApp01  
{  
  public partial class ViewModel : INotifyPropertyChanged  
  {  
    public ViewModel()  
    {  
      TrulyObservableCollection col = new TrulyObservableCollection();  
      for (int i = 1; i < 10; i++) col.Add(new Data() { ID = i, Number = 0 });  
      col.CollectionChanged += (sender, e) => { OnPropertyChanged(nameof(Cmd)); };  
      cvs.Source = col;  
    }  
    private CollectionViewSource cvs = new CollectionViewSource();  
    public ICollectionView View { get => cvs.View; }  
  
    public ICommand Cmd { get => new RelayCommand(CmdExec, CanCmdExec); }  
    private void CmdExec(Object obj)  
    {  
      //   
    }  
    private bool CanCmdExec(object obj)  
    {  
      foreach (var item in View)  
      {  
        var d = item as Data;  
        if (d != null && !string.IsNullOrEmpty(d.Error)) return false;  
      }  
      return true;  
    }  
    public event PropertyChangedEventHandler PropertyChanged;  
    private void OnPropertyChanged([CallerMemberName] string propName = "") =>  
      PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propName));  
  }  
  
  public class TransformerNumberValidationRule : ValidationRule  
  {  
    public override ValidationResult Validate(object value, CultureInfo cultureInfo)  
    {  
      var be = value as BindingExpression;  
      if (be == null) return new ValidationResult(false, "Invalid use of validation");  
      var d = be.DataItem as Data;  
      if (d == null) return new ValidationResult(false, "Invalid use of validation");  
      if (!string.IsNullOrEmpty(d.Error)) return new ValidationResult(false, "Please enter a value in the range: 10 - 50");  
      return new ValidationResult(true, null);  
    }  
  }  
  
  public sealed class TrulyObservableCollection : ObservableCollection where T : INotifyPropertyChanged  
  {  
    public TrulyObservableCollection() => CollectionChanged += FullObservableCollectionCollectionChanged;  
    public TrulyObservableCollection(IEnumerable pItems) : this()  
    {  
      foreach (var item in pItems) this.Add(item);  
    }  
    private void FullObservableCollectionCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)  
    {  
      if (e.NewItems != null) foreach (Object item in e.NewItems) ((INotifyPropertyChanged)item).PropertyChanged += ItemPropertyChanged;  
      if (e.OldItems != null) foreach (Object item in e.OldItems) ((INotifyPropertyChanged)item).PropertyChanged -= ItemPropertyChanged;  
    }  
    private void ItemPropertyChanged(object sender, PropertyChangedEventArgs e) => OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Replace, sender, sender, IndexOf((T)sender)));  
  }  
  
  public class RelayCommand : ICommand  
  {  
    private readonly Predicate

Answer

Hi,

Welcome to our Microsoft Q&A platform!

You can try my code.When the TextBox value is greater than 100, show an error.

  private void TxtNumber_TextChanged(object sender, TextChangedEventArgs e)  
        {  
            TextBox tb = sender as TextBox;  
            Button1.IsEnabled = Validation.GetHasError(tb) == true ? false : true;  
        }

Thanks.

Using validation rules to disable a button

1 additional answer