C# IValueConverter接口用法举例

介绍

IValueConverter接口位于名称空间System.Windows.Data，接口定义了Convert和ConvertBack两组方法：.

 public interface IValueConverter
    {
        object Convert(object value, Type targetType, object parameter, CultureInfo culture);
        object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture);
    }
}

在界面控件所需数据类型或格式和后台绑定的数据不一致时，往往需要借助IValueConverter接口进行转换。

举例

•   界面添加一个表格控件datagrid，绑定数据结构StudentList，StudentList这是一个ObservableCollection<Students>集合；

• Students数据模型定义如下：其中重写了ToString方法，并定义了四个属性，分别是Id，Name ，Age 和AgeValidate ，AgeValidate 用来验证数据，即年龄小于16或者大于21,时界面字体显示红色

[AddINotifyPropertyChangedInterface]
    public class Students 
    {
        private int id;
        public int Id
        {
            get { return id; }
            set
            {
                id = value;
            }
        }
        public string Name { get; set; }

        private int age;
        public int Age 
        {
            get { return age; }
            set
            {
                age = value;
                if(age < 16 || age > 21 )
                {
                    AgeValidate = true;
                }
                else
                {
                    AgeValidate = false;
                }
            }
        }
        public bool AgeValidate { get; set; }
        public override string ToString()
        {
            StringBuilder report = new StringBuilder();
            report.AppendLine($"[Id]  = [{Id}]");
            report.AppendLine($"[Name]  = [{Name}]");
            report.AppendLine($"[Age]  = [{Age}]");
            report.AppendLine($"[AgeValidate]  = [{AgeValidate}]");
            return report.ToString();
        }
    }

界面前台绑定：主要是通过这句

 Foreground="{Binding AgeValidate,Converter={StaticResource ShowColorConverter}}"

datagrid全部的代码如下：

<DataGrid Name="dgSourceData" AutoGenerateColumns="False" ItemsSource="{Binding StudentList}" 
                  ContextMenu="{Binding menu1}" RowHeaderWidth="30"  SelectedItem ="{Binding SelectedItems}" SelectionMode="Single" SelectionUnit="Cell"
                                cal:Message.Attach="[Event SelectionChanged]=[GridControl_SelectionChanged($source,$eventArgs)];" 
                               CellEditEnding="dgSourceData_BeginningEdit" SelectionChanged="dgSourceData_SelectionChanged" >
            <DataGrid.Columns>
                <DataGridTextColumn Header="Name"  Binding="{ Binding Path=Name}" MinWidth="68"/>
                <DataGridTemplateColumn  Header="Age"  MinWidth="68" >
                    <DataGridTemplateColumn.CellTemplate>
                        <DataTemplate>
                            <TextBox Text="{Binding Path=Age,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" 
                                     Foreground="{Binding AgeValidate,Converter={StaticResource ShowColorConverter}}" />
                        </DataTemplate>
                    </DataGridTemplateColumn.CellTemplate>
                </DataGridTemplateColumn>
                <DataGridTextColumn Header="Id"  Binding="{ Binding Path=Id}" MinWidth="48"/>
            </DataGrid.Columns>
        </DataGrid>

定义资源

<UserControl.Resources>
        <converters:ShowColorConverter x:Key="ShowColorConverter" />
    </UserControl.Resources>

IValueConverter接口实现：注意需要将object类型的value转换为我们的目标类型bool量

public class ShowColorConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            var flag = (bool)value;
            if (flag)
            {
                return "Red";
            }
            else
            {
                return "Black";
            }
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }

运行演示：