程式學習備忘錄

利用IDataErrorInfo可以在介面上輸入錯誤時，告知使用者輸入的值是錯的。

基本上是 View-Model 要實作 IDataErrorInfo，XAML上要撰寫 Validation.ErrorTemplate，

再加上 Validation.HasError 要觸發 Trigger 修改 ToolTip。

程式碼如下:

<Window x:Class="IDataErrorInfo介面範例.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:IDataErrorInfo介面範例"
        Title="MainWindow" Height="350" Width="525">
    <Window.DataContext>
        <local:VM/>
    </Window.DataContext>
    <Window.Resources>
        <Style TargetType="{x:Type TextBox}">
            <Style.Triggers>
                <!--Trigger to Set the tooltip to inform abort the error.-->
                <Trigger Property="Validation.HasError" Value="True">
                    <Setter Property="ToolTip" 
                            Value="{Binding RelativeSource={x:Static RelativeSource.Self},
                            Path=(Validation.Errors)[0].ErrorContent}"/>
                </Trigger>                
            </Style.Triggers>
            <Setter Property="Validation.ErrorTemplate">
                <Setter.Value>
                    <ControlTemplate>
                        <AdornedElementPlaceholder>
                            <Border BorderBrush="Red" BorderThickness="2"/>
                        </AdornedElementPlaceholder>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
    </Window.Resources>
    <Grid>
        <TextBox HorizontalAlignment="Left" Height="45" Margin="38,70,0,0" 
                 TextWrapping="Wrap" 
                 Text="{Binding MyValue,UpdateSourceTrigger=PropertyChanged,ValidatesOnDataErrors=True}"
                 VerticalAlignment="Top" Width="313"/>
        <Label Content="猜猜我的英文名字?" HorizontalAlignment="Left" Height="24" Margin="38,41,0,0" VerticalAlignment="Top" Width="304"/>
        <Label Margin="10,268,10,10" Content="{Binding Error}" Foreground="Red"/>

    </Grid>
</Window>

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Text;

namespace IDataErrorInfo介面範例
{
    public class VM:INotifyPropertyChanged, IDataErrorInfo
    {

        public event PropertyChangedEventHandler PropertyChanged;
        protected void OnPropertyChanged(string PropertyName)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(PropertyName));
        }


        private string _MyValue;
        public string MyValue
        {
            get { return _MyValue; }
            set { 
                _MyValue = value;
                OnPropertyChanged("MyValue");
            }
        }
        private string _ValidationErrorMsg;

        //給 view 顯示目前的錯誤訊息
        public string Error
        {
            get { return _ValidationErrorMsg; }
            set
            {
                _ValidationErrorMsg = value;
                OnPropertyChanged("Error");
            }
        }

        public string this[string columnName]
        {
            get 
            {
                string errmsg = "";
                if (columnName == "MyValue")
                {
                    int i = string.Compare(this.MyValue, "Alvin");
                    if (i == 0)
                    {
                        errmsg = "";
                    }
                    else
                    {
                        errmsg = "這不是我的名字!";
                    }
                }

                this.Error = errmsg;
                return errmsg;
            }
        }
    }
}