Question

我正在为我的研究使用MVVM模式（MVVM Light框架）编写一个小型UWP项目，并在许多场景和控件中遇到了绑定问题。

我已经努力将其中一个分为可用的小型示例项目here。

ProgressRing控件的IsActive属性对ViewModel方面的更新没有做出反应，即使它具有：

实施INotifyPropertyChanged
绑定模式明确设置为TwoWay绑定
UpdateSourceTrigger显式设置为PropertyChanged

MainPage.xaml中

<Page
    x:Class="TestProgressRing.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:core="using:Microsoft.Xaml.Interactions.Core"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:i="using:Microsoft.Xaml.Interactivity"
    xmlns:local="using:TestProgressRing"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    Width="491.282"
    Height="492.308"
    DataContext="{Binding MainPageViewModel, Source={StaticResource ResourceKey=Locator}}"
    mc:Ignorable="d">
    <Grid
        Width="500"
        Height="800"
        Margin="0,0,-8.667,-307.667"
        HorizontalAlignment="Left"
        VerticalAlignment="Top"
        Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
        <Grid.RowDefinitions>
            <RowDefinition Height="*" />
            <RowDefinition Height="3*" />
        </Grid.RowDefinitions>
        <Button
            Grid.Row="0"
            Width="250"
            Height="50"
            Margin="0"
            HorizontalAlignment="Center"
            VerticalAlignment="Center"
            Content="Boom">
            <i:Interaction.Behaviors>
                <core:EventTriggerBehavior EventName="Click">
                    <core:InvokeCommandAction Command="{Binding ClickCommand}" />
                </core:EventTriggerBehavior>
            </i:Interaction.Behaviors>
        </Button>
        <ProgressRing
            Grid.Row="1"
            Width="500"
            Height="500"
            Margin="0"
            HorizontalAlignment="Left"
            VerticalAlignment="Top"
            IsActive="{Binding IsLoading, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}"
            Visibility="Visible" />
    </Grid>
</Page>

MainPageViewModel.cs

using GalaSoft.MvvmLight;
using GalaSoft.MvvmLight.Command;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Input;

namespace TestProgressRing
{
    public class MainPageViewModel : ViewModelBase
    {
        private bool _isLoading;
        public bool IsLoading
        {
            get => _isLoading;
            set
            {
                _isLoading = value;
                Set(() => IsLoading, ref _isLoading, value);
            }
        }

        public ICommand ClickCommand { get; set; }

        public MainPageViewModel()
        {
            ClickCommand = new RelayCommand(() => 
            IsLoading = !IsLoading);
        }
    }
}

UWP控件是否仅仅适用于常规Binding而不是x：Bind？还有更多问题，例如CalendarPickerView Date属性也不想合作。

Answer 1

首先，您在绑定中不需要UpdateSourceTrigger=PropertyChanged, Mode=TwoWay。它始终是源到目标（即OneWay）。

真正的问题是，您不应该设置_isLoading = value;，因为它已作为ref传入，以检查属性值是否已更改。

因此，删除此行将使您的代码正常工作。您甚至可以将其简化为

private bool _isLoading;
public bool IsLoading
{
    get => _isLoading;
    set => Set(ref _isLoading, value);
}

Answer 2

尝试将绑定更改为：

IsActive="{Binding IsLoading}"

您的房产代码为：

    private bool _isLoading;
    public bool IsLoading
    {
        get {return _isLoading;}
        set
        {
            _isLoading = value;
            NotifyOfPropertyChange(nameof(IsLoading));
        }
    }

我已经使用了来自INotifyPropertyChanged框架的Caliburn.Micro的实现，但它可以是任何其他有效的实现;）

ProgressRing IsActive属性未更新

2 个答案: