(WPF) MVVM: ComboBox Binding

基本思路还是在View的Xmal里面绑定ViewModel的属性，虽然在View的后台代码中也可以实现binding，但是还是在Xmal里面相对的代码量要少一些。

此例子要实现的效果就是将一个List<Customer> 绑定到一个ComboBox，并将选择后的Customer的Age显示在一个TextBlock中。

1. Model

    public class Customer
    {
        public string Name
        {
            get;
            set;
        }

        public int Age
        {
            get;
            set;
        }
    }

2. ViewModel

    public class CustomerViewModel : ViewModelBase
    {
        private List<Customer> customers;

        private Customer selectedCustomer; 

        public CustomerViewModel()
        {
            this.customers = new List<Customer>()
            {
                new Customer { Name = "Paul", Age = 28 },
                new Customer { Name = "Fred", Age = 37 },
                new Customer { Name = "Cherry", Age = 21 },
            };

            this.selectedCustomer = new Customer();
        }

        public List<Customer> Customers
        {
            get
            {
                return this.customers;
            }
            set
            {
                if (!this.customers.Equals(value))
                {
                    this.customers = value;
                    base.OnPropertyChanged("Customers");
                }
            }
        }

        public Customer SelectedCustomer
        {
            get
            {
                return this.selectedCustomer;
            }
            set
            {
                if (!this.selectedCustomer.Equals(value))
                {
                    this.selectedCustomer = value;
                    base.OnPropertyChanged("SelectedCustomer");
                }
            }
        }
    }

3. View.

<UserControl x:Class="WpfApplication1.View.CustomerView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:vm="clr-namespace:WpfApplication1.ViewModel"
             mc:Ignorable="d"
             Height="308.072"
             Width="457.399">
    <UserControl.DataContext>
        <vm:CustomerViewModel/>
    </UserControl.DataContext>
    <Grid>
        <ComboBox HorizontalAlignment="Left"
                  Margin="45,47,0,0"
                  VerticalAlignment="Top"
                  Width="120"
                  Height="31"
                  ItemsSource="{Binding Customers}"
                  SelectedItem="{Binding SelectedCustomer}"
                  DisplayMemberPath="Name"/>
        <TextBlock HorizontalAlignment="Left"
                   Margin="212,52,0,0"
                   TextWrapping="Wrap"
                   Text="{Binding SelectedCustomer.Age}"
                   VerticalAlignment="Top"
                   Height="26"
                   Width="101" />

    </Grid>
</UserControl>

还有其他供选择的binding方式如下：

    <TextBlock Text="Example 1" VerticalAlignment="Center"/>
            <ComboBox ItemsSource="{Binding MyStringOptions}" Grid.Column="1" SelectedItem="{Binding SelectedOption1}" Margin="5"/>
            <TextBlock Text="{Binding SelectedOption1}" Grid.Column="2" Margin="10,5,5,0" VerticalAlignment="Center"/>

            <TextBlock Grid.Row="1" Text="Example 2" VerticalAlignment="Center"/>
            <ComboBox Grid.Row="1" Grid.Column="1" ItemsSource="{Binding MyClassOptions}" SelectedItem="{Binding SelectedClass}" DisplayMemberPath="Name" Margin="5"/>
            <TextBlock Grid.Row="1" Grid.Column="2" Margin="10,5,5,0" VerticalAlignment="Center"><Run Text="{Binding SelectedClass.Name}"/><Run Text=" - "/><Run Text="{Binding SelectedClass.Age}"/></TextBlock>

            <TextBlock Grid.Row="2" Text="Example 3" VerticalAlignment="Center"/>
            <ComboBox Grid.Row="2" Grid.Column="1" ItemsSource="{Binding MyClassOptions}" SelectedValuePath="Age" SelectedValue="{Binding SelectedAge}" DisplayMemberPath="Name" Margin="5"/>
            <TextBlock Grid.Row="2" Grid.Column="2" Margin="10,5,5,0" VerticalAlignment="Center"><Run Text="Selected age: "/><Run Text="{Binding SelectedAge}"/></TextBlock>

            <TextBlock Grid.Row="3" Text="Example 4" VerticalAlignment="Center"/>
            <ComboBox Grid.Row="3" Grid.Column="1" ItemsSource="{Binding MyClassOptions}" SelectedValuePath="Age" SelectedValue="{Binding SelectedAge}" ItemTemplate="{StaticResource Example4ItemTemplate}" Margin="5"/>
            <TextBlock Grid.Row="3" Grid.Column="2" Margin="10,5,5,0" VerticalAlignment="Center"><Run Text="Selected age: "/><Run Text="{Binding SelectedAge}"/></TextBlock>

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