WPF 体验数据邦定(二)

上一节，提到了控制空值的TargetNullValue。本节介绍下另外两个跟绑定有关的关键字：StringFormat，FallbackValue。

StringFormat，顾名思义就是格式化字符串，在数据绑定的过程中，这个当然很重要了，谁不爱美阿。先看看上节的例子：

<Window x:Class="WpfProject.Test"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Test" Height="300" Width="300" Loaded="Window_Loaded">
    <Grid>
        <ListBox Name="lbxPersons">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel Orientation="Horizontal">
                        <TextBlock Text="{Binding FirstName}" Width="50" />
                        <TextBlock Text="{Binding LastName}" Width="50" />
                        <TextBlock Text="{Binding Age, TargetNullValue='Age Unknown'}"  />
                    </StackPanel>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
    </Grid>
</Window>

为了很好的显示我们所需要的数据，用了三个TextBlock，显得很啰嗦有很吃力，那么有没有更好的方法呢，用MultiBinding和StringFormat。

<Window x:Class="WpfProject.Test"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="clr-namespace:System.Windows.Data;assembly=PresentationFramework"    
    Title="Test" Height="300" Width="300" Loaded="Window_Loaded">
    <Grid>
        <ListBox Name="lbxPersons">  
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <TextBlock>
                        <TextBlock.Text>
                            <MultiBinding  StringFormat="{}{0}-{1},{2}">
                                <Binding Path="FirstName"/>
                                 <Binding Path="LastName"/>
                                 <Binding Path="Age" TargetNullValue='Age Unknown'/>                                
                            </MultiBinding>
                        </TextBlock.Text>
                    </TextBlock>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
    </Grid>
</Window>

FallbackValue设置邦定不存在时显示的信息。还是上面的例子，Person类里不存在Birthday属性，我们在绑定里添加，让它显示不存在。

<Window x:Class="WpfProject.Test"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"         
    Title="Test" Height="300" Width="300" Loaded="Window_Loaded">
    <Grid>
        <ListBox Name="lbxPersons">  
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <TextBlock>
                        <TextBlock.Text>
                            <MultiBinding  StringFormat="{}{0}-{1},{3},{2}">
                                <Binding Path="FirstName"/>
                                 <Binding Path="LastName"/>
                                 <Binding Path="Age" TargetNullValue='Age Unknown'/>   
                                <Binding Path="Birthday" FallbackValue='Birthday Unknown'/>  
                            </MultiBinding>
                        </TextBlock.Text>
                    </TextBlock>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
    </Grid>
</Window>

运行：

OK。

<Window x:Class="WpfProject.Test"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"         
    Title="Test" Height="300" Width="300" Loaded="Window_Loaded">
    <Grid>
        <ListBox Name="lbxPersons">  
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <TextBlock>
                        <TextBlock.Text>
                            <MultiBinding  StringFormat="{}{0}-{1},{3},{2}">
                                <Binding Path="FirstName"/>
                                 <Binding Path="LastName"/>
                                 <Binding Path="Age" TargetNullValue='Age Unknown'/>   
                                <Binding Path="Birthday" FallbackValue='Birthday Unknown'/>  
                            </MultiBinding>
                        </TextBlock.Text>
                    </TextBlock>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
    </Grid>
</Window>