在MahApps控件中，在加载表单时会触发验证事件，我需要在单击按钮后显示验证消息

Question

IDataErrorInfo: Validating when page submitted

Here I am using IdataErrorInfo

Below is My MainwindowViewModel Class COde

using System;
using System.Collections.Generic;
using System.Linq;
using System.ComponentModel;
using System.Globalization;
using System.Threading;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;
using MahApps.Metro;
using MetroDemo.Models;
using System.Windows.Input;
using MahApps.Metro.Controls;
using MahApps.Metro.Controls.Dialogs;

namespace MetroDemo
{
    public class AccentColorMenuData
    {
        public string Name { get; set; }
        public Brush BorderColorBrush { get; set; }
        public Brush ColorBrush { get; set; }

        private ICommand changeAccentCommand;

        public ICommand ChangeAccentCommand
        {
            get { return this.changeAccentCommand ?? (changeAccentCommand = new SimpleCommand { CanExecuteDelegate = x => true, ExecuteDelegate = x => this.DoChangeTheme(x) }); }
        }

        protected virtual void DoChangeTheme(object sender)
        {
            var theme = ThemeManager.DetectAppStyle(Application.Current);
            var accent = ThemeManager.GetAccent(this.Name);
            ThemeManager.ChangeAppStyle(Application.Current, accent, theme.Item1);
        }
    }

    public class AppThemeMenuData : AccentColorMenuData
    {
        protected override void DoChangeTheme(object sender)
        {
            var theme = ThemeManager.DetectAppStyle(Application.Current);
            var appTheme = ThemeManager.GetAppTheme(this.Name);
            ThemeManager.ChangeAppStyle(Application.Current, theme.Item2, appTheme);
        }
    }

    public class MainWindowViewModel : INotifyPropertyChanged, IDataErrorInfo
    {
        private readonly IDialogCoordinator _dialogCoordinator;
        int? _integerGreater10Property;
        int? _emptystring;

        private bool _animateOnPositionChange = true;

        public MainWindowViewModel(IDialogCoordinator dialogCoordinator)
        {
            _dialogCoordinator = dialogCoordinator;
            SampleData.Seed();

            // create accent color menu items for the demo
            this.AccentColors = ThemeManager.Accents
                                            .Select(a => new AccentColorMenuData() { Name = a.Name, ColorBrush = a.Resources["AccentColorBrush"] as Brush })
                                            .ToList();

            // create metro theme color menu items for the demo
            this.AppThemes = ThemeManager.AppThemes
                                           .Select(a => new AppThemeMenuData() { Name = a.Name, BorderColorBrush = a.Resources["BlackColorBrush"] as Brush, ColorBrush = a.Resources["WhiteColorBrush"] as Brush })
                                           .ToList();


            Albums = SampleData.Albums;
            Artists = SampleData.Artists;

            FlipViewTemplateSelector = new RandomDataTemplateSelector();

            FrameworkElementFactory spFactory = new FrameworkElementFactory(typeof(Image));
            spFactory.SetBinding(Image.SourceProperty, new System.Windows.Data.Binding("."));
            spFactory.SetValue(Image.HorizontalAlignmentProperty, HorizontalAlignment.Stretch);
            spFactory.SetValue(Image.StretchProperty, Stretch.Fill);
            FlipViewTemplateSelector.TemplateOne = new DataTemplate()
            {
                VisualTree = spFactory
            };
            FlipViewImages = new string[] { "http://trinities.org/blog/wp-content/uploads/red-ball.jpg", "http://savingwithsisters.files.wordpress.com/2012/05/ball.gif" };

            RaisePropertyChanged("FlipViewTemplateSelector");


            BrushResources = FindBrushResources();

            CultureInfos = CultureInfo.GetCultures(CultureTypes.InstalledWin32Cultures).ToList();
        }

        public string Title { get; set; }
        public int SelectedIndex { get; set; }
        public List<Album> Albums { get; set; }
        public List<Artist> Artists { get; set; }
        public List<AccentColorMenuData> AccentColors { get; set; }
        public List<AppThemeMenuData> AppThemes { get; set; }
        public List<CultureInfo> CultureInfos { get; set; }

        public int? IntegerGreater10Property
        {
            get { return this._integerGreater10Property; }
            set
            {
                if (Equals(value, _integerGreater10Property))
                {
                    return;
                }

                _integerGreater10Property = value;
                RaisePropertyChanged("IntegerGreater10Property");
            }
        }


        public string FirstName { get; set; }
        public string LastName { get; set; }

        DateTime? _datePickerDate;
        public DateTime? DatePickerDate
        {
            get { return this._datePickerDate; }
            set
            {
                if (Equals(value, _datePickerDate))
                {
                    return;
                }

                _datePickerDate = value;
                RaisePropertyChanged("DatePickerDate");
            }
        }







        bool _magicToggleButtonIsChecked = true;
        public bool MagicToggleButtonIsChecked
        {
            get { return this._magicToggleButtonIsChecked; }
            set
            {
                if (Equals(value, _magicToggleButtonIsChecked))
                {
                    return;
                }

                _magicToggleButtonIsChecked = value;
                RaisePropertyChanged("MagicToggleButtonIsChecked");
            }
        }

        private bool _quitConfirmationEnabled;
        public bool QuitConfirmationEnabled
        {
            get { return _quitConfirmationEnabled; }
            set
            {
                if (value.Equals(_quitConfirmationEnabled)) return;
                _quitConfirmationEnabled = value;
                RaisePropertyChanged("QuitConfirmationEnabled");
            }
        }


            }
        }


            }
        }

        public event PropertyChangedEventHandler PropertyChanged;



        /// <summary>
        /// Raises the PropertyChanged event if needed.
        /// </summary>
        /// <param name="propertyName">The name of the property that changed.</param>
        protected virtual void RaisePropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }

        public string this[string columnName]
        {
            get
            {

                if (columnName == "IntegerGreater10Property" && this.IntegerGreater10Property < 10)
                {
                    return "Number is not greater than 10!";
                }

                if (columnName == "DatePickerDate" && this.DatePickerDate == null)
                {
                    return "No Date given!";
                }

                if (columnName == "FirstName")
                {
                    if (string.IsNullOrEmpty(FirstName) || FirstName.Length < 3)
                        return "Please Enter  First Name";
                }
                if (columnName == "LastName")
                {
                    if (string.IsNullOrEmpty(FirstName) || FirstName.Length < 3)
                        return "Please Enter Last Name";
                }

                return null;
            }
        }

        public string Error { get { return string.Empty; } }

        private ICommand singleCloseTabCommand;

        public ICommand SingleCloseTabCommand
        {
            get
            {
                return this.singleCloseTabCommand ?? (this.singleCloseTabCommand = new SimpleCommand
                {
                    CanExecuteDelegate = x => true,
                    ExecuteDelegate = async x =>
                    {
                        await ((MetroWindow) Application.Current.MainWindow).ShowMessageAsync("Closing tab!", string.Format("You are now closing the '{0}' tab", x));
                    }
                });
            }
        }

        private ICommand neverCloseTabCommand;

        public ICommand NeverCloseTabCommand
        {
            get { return this.neverCloseTabCommand ?? (this.neverCloseTabCommand = new SimpleCommand { CanExecuteDelegate = x => false }); }
        }


        private ICommand showInputDialogCommand;

        public ICommand ShowInputDialogCommand
        {
            get
            {
                return this.showInputDialogCommand ?? (this.showInputDialogCommand = new SimpleCommand
                {
                    CanExecuteDelegate = x => true,
                    ExecuteDelegate = x =>
                    {
                        _dialogCoordinator.ShowInputAsync(this, "From a VM", "This dialog was shown from a VM, without knowledge of Window").ContinueWith(t => Console.WriteLine(t.Result));
                    }
                });
            }
        }




        private ICommand showProgressDialogCommand;

        public ICommand ShowProgressDialogCommand
        {
            get
            {
                return this.showProgressDialogCommand ?? (this.showProgressDialogCommand = new SimpleCommand
                {
                    CanExecuteDelegate = x => true,
                    ExecuteDelegate = x => RunProgressFromVm()
                });
            }
        }










    }
}

Below is My XAml Code

  <TextBox  Name="txt_LA_FirstName"
                         Controls:TextBoxHelper.Watermark="First Name"
                         Controls:TextBoxHelper.UseFloatingWatermark="True"
                         ToolTip="First Name" Grid.Row="2" Grid.Column="1" VerticalAlignment="Center" HorizontalAlignment="Stretch"  Text="{Binding FirstName, ValidatesOnDataErrors=True, UpdateSourceTrigger=PropertyChanged, NotifyOnValidationError=True}" />

Event Is Raising at form load and showing Error Messages Before user enters any Value> I need to show Error Messages After Button Click Event

Answer 1

The reason why you get it is because the content of your indexer is static, so the View validates it during the binding. You should only validate it when the property changes though.

You should have a backing field for an errors dictionary with Add/Remove methods, like this

    private readonly Dictionary<string, string> errors = new Dictionary<string, string>();
    public string this[string columnName]
    {
        get
        {
            string errorMessage = null;
            if (errors.TryGetValue(columnName, errorMessage) 
            {
                return errorMessage;
            }

            return null;
        }
    }

    protected void AddErrorMessage(string columnName, string errorMessage) 
    {
        errors[columnName] = errorMessage;
    }
    protected void RemoveErrorMessage(string columnName) 
    {
         if(errors.ContainsKey(columnName)) 
        {
            errors.Remove(columnName);
        }
    }

    protected virtual void Validate() 
    {
            errors.Clear();
            if (this.IntegerGreater10Property < 10)
            {
                this.AddErrorMessage("IntegerGreater10Property", "Number is not greater than 10!");
            }

            if (this.DatePickerDate == null)
            {
                this.AddErrorMessage("DatePickerDate", "No Date given!");
            }

            if (string.IsNullOrEmpty(FirstName) || FirstName.Length < 3)
            {
                this.AddErrorMessage("FirstName", "Please Enter  First Name");
            }

            if (string.IsNullOrEmpty(LastName) || Lastname.Length < 3)
            {
                this.AddErrorMessage("LastName", "Please Enter Last Name");
            }
    }

And then remove them with RemoveMessage("FirstName") or clear it up on validation. You should implement this in a base class of course, to avoid repeating this code over and over again and just override the Validate() method in your ViewModel classes

Answer 2

Thanks for your reply

Even I tried it I had solved it By creating on Bool variable and declaring it as False in MainwindowView model class.

Unless and Until the Bool Variable is True it wont Validates

On Button click Event I will Enable the bool Variable to True then It starts Validates on Button CLick

if (Enable)
                {



                    if (columnName == "IntegerGreater10Property" && this.IntegerGreater10Property < 10)
                    {
                        return "Number is not greater than 10!";
                    }

                    if (columnName == "DatePickerDate" && this.DatePickerDate == null)
                    {
                        return "No Date given!";
                    }

                    if (columnName == "FirstName")
                    {
                        if (string.IsNullOrEmpty(FirstName) || FirstName.Length < 3)
                            return "Please Enter  First Name";
                    }
                    if (columnName == "LastName")
                    {
                        if (string.IsNullOrEmpty(FirstName) || FirstName.Length < 3)
                            return "Please Enter Last Name";
                    }
                }
                return null;

Below is My Button click Event (On Button I will Enable the Bool Property to true

 var x = (MainWindowViewModel)DataContext;
            x.Enable = true;

            var binding = txt_LA_FirstName.GetBindingExpression(TextBox.TextProperty);
            binding.UpdateSource();