WPF数据编辑的提交与撤销

当为一个集合（通常绑定在DataGrid或其它ItemsControl控件）添加或编辑一个项时，通常会弹出一个编辑界面编辑项的属性，编辑结束再提交，或者我们不想编辑数据了，此时选择取消，数据项的内容没有任何改变。

在将数据项绑定到编辑界面时，我们可以定义绑定源更新的触发方式，如下代码所示，将TextBox的Text属性的绑定设置为 UpdateSourceTrigger="Explicit"，此时需要手动触发数据源的更新。

   <TextBox.Text>
        <Binding Path="Age" UpdateSourceTrigger="Explicit" >
            <Binding.ValidationRules>
                <validateRule:AgeRangeRule Min="21" Max="130" ValidationStep="ConvertedProposedValue"/>
            </Binding.ValidationRules>
        </Binding>
    </TextBox.Text>

但上述方法的缺点是不会触发验证，这个缺点很要命，我们通常需要数据验证来可视化反馈输入错误，并提示用户输入规范的内容。

官方提供的解决方案是，使用BindingGroup及让数据类实现IEditableObject接口，实现该接口的方法以提供数据的提交、撤销和结束。下面的是一个数据类的定义，实际的数据由Empolyee类存储，它定义在EmployeeEditAgent的内部实现，EmployeeEditAgent相当于Empolyee的代理，它实现了IEditableObject接口，EmployeeEditAgent中定义了当前数据currentEmployee 和备份数据copyEmployee ，当调用BeginEdit方法时，currentEmployee复制给currentEmployee，在调用CancelEdit方法，currentEmployee 复制给currentEmployee，这里的复制是深层拷贝，通过备份和恢复的方式实现数据的撤销编辑。

    public class EmployeeEditAgent : INotifyPropertyChanged, IEditableObject
    {

        [Serializable]
        class Employee
        {
            internal string Name { get; set; }
            internal int Age { get; set; }
            internal float Salary { get; set; }
        }
        private Employee copyEmployee = null;
        private Employee currentEmployee = new Employee();

        public string Name
        {
            get { return currentEmployee.Name; }
            set
            {
                if (currentEmployee.Name != value)
                {
                    currentEmployee.Name = value;
                    RaisePropertyChanged("Name");
                }
            }
        }

        public int Age
        {
            get { return currentEmployee.Age; }
            set
            {
                if (currentEmployee.Age != value)
                {
                    currentEmployee.Age = value;
                    RaisePropertyChanged("Age");
                }
            }
        }

        public float Salary
        {
            get { return currentEmployee.Salary; }
            set
            {
                if (currentEmployee.Salary != value)
                {
                    currentEmployee.Salary = value;
                    RaisePropertyChanged("Salary");
                }
            }
        }

        #region Implementation of INotifyPropertyChanged

        public event PropertyChangedEventHandler PropertyChanged = delegate { };

        public void RaisePropertyChanged(string propertyname)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyname));
        }
        #endregion

        #region Implementation of IEditableObject

        public void BeginEdit()
        {
            copyEmployee = DeepColone(currentEmployee);
        }

        public void EndEdit()
        {
            copyEmployee = null;
        }

        public void CancelEdit()
        {
            currentEmployee = DeepColone(copyEmployee);
            RaisePropertyChanged("");
        }

        #endregion

        private T  DeepColone<T>(T t)
        {
            MemoryStream stream = new MemoryStream();
            BinaryFormatter formatter = new BinaryFormatter();
            formatter.Serialize(stream, t);
            stream.Position = 0;
            return (T)formatter.Deserialize(stream);
        }
    }

定义了数据类，还要了解BindingGroup类，BindingGroup可以同时更新多个绑定源，如果某个绑定验证不通过，则提交失败。调用BindingGroup的方法会相应调用绑定源实现的IEditableObject接口的方法：

BindingGroup	IEditableObject
BeginEdit	BeginEdit	开始编辑
CommitEdit	EndEdit	提交编辑
CancelEdit	CancelEdit	取消编辑

FrameworkElement 或 FrameworkContentElement 都有 BindingGroup 属性，对于上面的定义个数据类，通常我们将其三个属性分别绑定到三个TextBox上，而三个控件通常位于同一个容器（StackPanel或Grid设置Window）内，此时将容器的DataContext设置为数据源，在容器上创建BindingGroup，此时三个TextBox会继承容器的BindingGroup，即当我们为任意一个TextBox设置绑定时，该绑定会添加到容器的BindingGroup中，这样便实现绑定的同时提交，下面是XAML的实现，注意代码注释说明：

<Window x:Class="WpfApplication2.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:validateRule="clr-namespace:ValidateRule"
        xmlns:wpfApplication2="clr-namespace:WpfApplication2"
        Title="数据验证演示" Height="217" Width="332">
    <Window.Resources>
        <wpfApplication2:Employee Name="MJ" Age="25" Salary="2500" x:Key="employee"></wpfApplication2:Employee>
        <ControlTemplate x:Key="validationTemplate">
            <DockPanel>
                <AdornedElementPlaceholder/>
                <TextBlock Foreground="Red" FontSize="20">!</TextBlock>
            </DockPanel>
        </ControlTemplate>

        <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>
    </Window.Resources>
    <Window.BindingGroup>
        <BindingGroup ></BindingGroup> <!--此处实例化了Window的BindingGroup属性-->
    </Window.BindingGroup>
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="118*"/>
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="29"/>
            <RowDefinition Height="110"/>
            <RowDefinition Height="100*"/>
        </Grid.RowDefinitions>
        <StackPanel Name="stackPanel"  Grid.Row="1" Margin="5" Loaded="stackPanel_Loaded"  >
            <!--<StackPanel.BindingGroup>
                <BindingGroup ></BindingGroup>
            </StackPanel.BindingGroup>-->
            <StackPanel Orientation="Horizontal"  >
                <Label Height="30">姓名</Label>
                <TextBox Width="70" Text="{Binding Path=Name}"></TextBox>
            </StackPanel>
            <StackPanel Orientation="Horizontal" Margin="0,5,0,0">
                <Label Height="30">年龄</Label>
                <TextBox Width="70" Validation.ErrorTemplate="{StaticResource validationTemplate}"
                                    Style="{StaticResource textBoxInError}">
                    <TextBox.Text>
                        <Binding Path="Age" UpdateSourceTrigger="PropertyChanged" >
                            <!--该绑定会添加到Window的BindingGroup-->
                            <Binding.ValidationRules>
                                <validateRule:AgeRangeRule Min="21" Max="130" ValidationStep="RawProposedValue"/>
                            </Binding.ValidationRules>
                        </Binding>
                    </TextBox.Text>

                </TextBox>
                <TextBlock TextWrapping="Wrap" Text="{Binding Path=Age}" Width="98"/>
            </StackPanel>
            <StackPanel Orientation="Horizontal" Margin="0,5,0,0">
                <Label Height="30">工资</Label>
                <TextBox Width="70" Text="{Binding Path=Salary}"></TextBox>
            </StackPanel>
        </StackPanel>
        <Label Content="员工信息" FontSize="15"/>
        <Button Content="提交" HorizontalAlignment="Left" Height="22" Margin="54,10,0,0" Grid.Row="2" VerticalAlignment="Top" Width="76" Click="Button_Click"/>
        <Button Content="取消" HorizontalAlignment="Left" Height="22" Margin="165,10,0,0" Grid.Row="2" VerticalAlignment="Top" Width="76" Click="Button_Click_1"/>
    </Grid>
</Window>

下面是代码的实现，注意BindingGroup三个方法BeginEdit、CommitEdit、CancelEdit的调用：

 public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
           // stackPanel.DataContext = new EmployeeEditAgent() { Name = "Mj", Age = 35, Salary = 2500 };
            this.DataContext = new EmployeeEditAgent() { Name = "Mj", Age = 35, Salary = 2500 };

        }

        private void stackPanel_Loaded(object sender, RoutedEventArgs e)
        {
          //  stackPanel.BindingGroup.BeginEdit();
            this.BindingGroup.BeginEdit();//开始编辑事务
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            //if (stackPanel.BindingGroup.CommitEdit())
            //{
            //    MessageBox.Show("success");
            //}
            //else
            //{
            //    MessageBox.Show("");
            //}
            if (this.BindingGroup.CommitEdit())//提交编辑
            {
                MessageBox.Show("success");
            }
            else
            {
                MessageBox.Show("failed");
            }
        }

        private void Button_Click_1(object sender, RoutedEventArgs e)
        {
            this.BindingGroup.CancelEdit();//取消编辑
        }
    }