自定义用户控件的DependencyProperty绑定不会在更改时更新 [英] Binding on DependencyProperty of custom User Control not updating on change
问题描述
我无法在自定义用户控件上进行数据绑定。我创建了一个示例项目来突出说明我的问题。我对WPF以及MVVM都是完全陌生的，所以请忍受...
I'm having difficulties with databinding on my custom user control (s). I created an example project to highlight my problem. I'm completely new to WPF and essentially MVVM as well, so bear with me...
我创建了一个简单的视图，该视图使用两种方式进行数据绑定。内置控件上的数据绑定工作正常。我的自定义控件没有...我在控件的 PropertyChangedCallback 中设置了一个断点。它在启动时会被击中一次，但是再也不会击中。同时，我绑定到相同值的标签正在愉快地递减计数。
I created a simple view that uses databinding two ways. The databinding on the built-in control works just fine. My custom control doesn't... I put a breakpoint in the PropertyChangedCallback of my control. It gets hit once on startup, but then never again. Meanwhile, the label I have bound to the same value is happily counting down.
我缺少什么？我的示例项目如下：
What am I missing? My example project follows:
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>
这是我的模型：
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：
The 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;
}
}
}
这是我的用户的XAML控制项：
Here's the XAML for my user control:
<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>
这是用户控件后面的代码：
And here's the code behind the user control:
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();
}
}
}
推荐答案
您的更改回调正在打破绑定。
Your change callback is breaking the binding.
作为框架：在您的窗口中，您有 UC.X = {Binding A } ，然后在该属性更改（在UC中）中，您有 X = B; 。这会破坏绑定，因为在两种情况下都设置了 X 。
As a skeleton: in your window you have UC.X="{Binding A}" and then in that property change (in UC) you have X=B;. This breaks the binding since in both cases you set X.
要纠正，请删除更改回调并将其添加到标签：
To rectify, remove change callback and add this to the label:
Content="{Binding MinutesRemaining, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type UserControl}}}"
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