在自定义用户控件的DependencyProperty上绑定不更新更新

Question

我在自定义用户控件上进行数据绑定时遇到了困难。 我创建了一个示例项目来突出我的问题。 我是WPF的新手，也是MVVM的新手，所以请耐心等待......

我创建了一个使用数据绑定两种方式的简单视图。 内置控件上的数据绑定工作正常。 我的自定义控件没有......我在我的控件的PropertyChangedCallback中放了一个断点。 它在启动时被击中一次，但从未再次被击中。 与此同时，我已经绑定到相同价值的标签很高兴倒计时。

我错过了什么？ 我的示例项目如下：

主窗口：

<Window x:Class="WpfMVVMApp.MainWindow"
        xmlns:local="clr-namespace:WpfMVVMApp"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Grid.DataContext>
            <local:CountdownViewModel />
        </Grid.DataContext>
        <Label Name="custName" Content="{Binding Path=Countdown.ChargeTimeRemaining_Mins}" Height="45" VerticalAlignment="Top"></Label>
        <local:UserControl1 MinutesRemaining="{Binding Path=Countdown.ChargeTimeRemaining_Mins}" Height="45"></local:UserControl1>
    </Grid>
</Window>

这是我的模特：

namespace WpfMVVMApp
{

    public class CountdownModel : INotifyPropertyChanged
    {
        private int chargeTimeRemaining_Mins;
        public int ChargeTimeRemaining_Mins
        {
            get
            {
                return chargeTimeRemaining_Mins;
            }
            set
            {
                chargeTimeRemaining_Mins = value;
                OnPropertyChanged("ChargeTimeRemaining_Mins");
            }
        }

        #region INotifyPropertyChanged Members
        public event PropertyChangedEventHandler PropertyChanged;
        private void OnPropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
        #endregion 
    }
}

ViewModel：

namespace WpfMVVMApp
{
    public class CountdownViewModel
    {
        public CountdownModel Countdown { get; set; }

        DispatcherTimer timer;
        private const int maxMins = 360;

        public CountdownViewModel()
        {
            Countdown = new CountdownModel { ChargeTimeRemaining_Mins = 60 };

            // Setup timers
            timer = new DispatcherTimer();
            timer.Tick += new EventHandler(this.SystemChargeTimerService);
            timer.Interval = new TimeSpan(0, 0, 1);
            timer.Start();
        }

        private void SystemChargeTimerService(object sender, EventArgs e)
        {
            //convert to minutes remaining
            // DEMO CODE - TODO: Remove
            this.Countdown.ChargeTimeRemaining_Mins -= 1;
        }
    }
}

这是我的用户控件的XAML：

<UserControl x:Class="WpfMVVMApp.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-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             mc:Ignorable="d" 
             d:DesignHeight="300" d:DesignWidth="300">
    <Grid>
        <Label Name="Readout"></Label>
    </Grid>
</UserControl>

这是用户控件背后的代码：

namespace WpfMVVMApp
{
    public partial class UserControl1 : UserControl
    {
        #region Dependency Properties
        public static readonly DependencyProperty MinutesRemainingProperty =
                    DependencyProperty.Register
                    (
                        "MinutesRemaining", typeof(int), typeof(UserControl1),
                        new UIPropertyMetadata(10, new PropertyChangedCallback(minutesRemainChangedCallBack))
                    );
        #endregion

        public int MinutesRemaining
        {
            get
            {
                return (int)GetValue(MinutesRemainingProperty);
            }
            set
            {
                SetValue(MinutesRemainingProperty, value);
            }
        }

        static void minutesRemainChangedCallBack(DependencyObject property, DependencyPropertyChangedEventArgs args)
        {
            UserControl1 _readout = (UserControl1)property;
            _readout.MinutesRemaining = (int)args.NewValue;

            _readout.Readout.Content = _readout.MinutesRemaining;
        }

        public UserControl1()
        {
            InitializeComponent();
        }
    }
}

Answer 1

您的更改回调正在破坏绑定。

作为一个骨架：在你的窗口中你有UC.X="{Binding A}"然后在那个属性改变（在UC中）你有X=B; 。 这会破坏绑定，因为在两种情况下都设置了X

要纠正，请删除更改回调并将其添加到标签：

 Content="{Binding MinutesRemaining, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type UserControl}}}"

Answer 2

我尝试了你的代码工作正常我唯一的改变是删除propertychangedcallback背后的代码，并将Label（读出）数据绑定到依赖属性。

用户控件（XAML）

<UserControl x:Class="WpfApplication1.UserControl"
         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" 
         mc:Ignorable="d" 
         d:DesignHeight="300" d:DesignWidth="300">
   <Grid>
       <Label Name="Readout" Content="{Binding RelativeSource={RelativeSource 
                            AncestorType=UserControl}, Path=MinutesRemaining}"/>
  </Grid>
</UserControl>

USERCONTROL（代码背后）

public partial class UserControl1 : UserControl
{
    #region Dependency Properties
    public static readonly DependencyProperty MinutesRemainingProperty =
                DependencyProperty.Register
                (
                    "MinutesRemaining", typeof(int), typeof(UserControl1),
                    new UIPropertyMetadata(10)
                );
    #endregion

    public int MinutesRemaining
    {
        get
        {
            return (int)GetValue(MinutesRemainingProperty);
        }
        set
        {
            SetValue(MinutesRemainingProperty, value);
        }
    }

   public UserControl1()
    {
        InitializeComponent();
    }
}