用户控件绑定在值更新时丢失，标准文本框控件不会发生这种情况

Question

我在用户控件中绑定有问题。这是我的用户控件：用户控件1.xaml<UserControl x:Class="WpfApp1.UserControl1"    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-ompatibility/2006"     xmlns:d="http://schemas.microsoft.com/expression/blend/2008"     xmlns:local="clr-namespace:WpfApp1"    mc:Ignorable="d"     x:Name="usercontrol"    d:DesignHeight="450" d:DesignWidth="800">    <Grid>        <TextBox Text="{Binding HmiField, ElementName=usercontrol}"/>    </Grid></UserControl>用户控件1.xaml.csnamespace WpfApp1{    public partial class UserControl1 : UserControl    {        public double HmiField        {            get { return (double)GetValue(HmiFieldProperty); }            set { SetValue(HmiFieldProperty, value); }        }        public static readonly DependencyProperty HmiFieldProperty =            DependencyProperty.Register("HmiField", typeof(double), typeof(UserControl1));        public UserControl1()        {            InitializeComponent();        }    }}这是主窗口：主窗口.xaml<Window x:Class="WpfApp1.MainWindow"        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"        xmlns:local="clr-namespace:WpfApp1"        mc:Ignorable="d"        DataContext="{Binding Md, RelativeSource={RelativeSource Self}}"        Title="MainWindow" Height="450" Width="800">    <UniformGrid>        <Button Content="{Binding Prop1}" Click="Button_Click"/>        <Label Content="{Binding Prop1}"/>        <TextBox Text="{Binding Prop1}"/>        <local:UserControl1 HmiField="{Binding Prop1}"/>    </UniformGrid></Window>

Answer 1

Binding 必须是 TwoWay，或者显式设置

<local:UserControl1 HmiField="{Binding Prop1, Mode=TwoWay}"/>

或默认情况下隐式：

public static readonly DependencyProperty HmiFieldProperty =

    DependencyProperty.Register(

        nameof(HmiField), typeof(double), typeof(UserControl1),

        new FrameworkPropertyMetadata(

            0d, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault));

TextBox 的Text属性注册如上所示，即带有BindsTwoWayByDefault标志。

在TextBoxUserControl 的 XAML 中的Binding 中，您可能还想在用户键入时更新源属性（而不是仅在失去焦点时）：

<TextBox Text="{Binding HmiField,

                ElementName=usercontrol,

                UpdateSourceTrigger=PropertyChanged}"/>

或者没有其他无用的生成usercontrol字段：

<TextBox Text="{Binding HmiField,

                RelativeSource={RelativeSource AncestorType=UserControl}

                UpdateSourceTrigger=PropertyChanged}"/>