c# - 为什么不显示标签的内容？

所以我有一个带有标签的 View ，我有一个 ViewModel。

View 模型库

public abstract class ViewModelBase : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void RaisePropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    protected virtual bool SetAndRaisePropertyChanged<T>(ref T storage, T value, [CallerMemberName] string propertyName = "")
    {
        if (EqualityComparer<T>.Default.Equals(storage, value))
            return false;
        storage = value;
        this.RaisePropertyChanged(propertyName);
        return true;
    }

    private void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }
}

这是 ViewModel 的样子:

  private string _balance = "1111$";
    public string Balance
    {
        get { return _balance; }
        set { SetAndRaisePropertyChanged(ref _balance, value); }
    }

这是 View :

    <UserControl x:Class="monei_project.MainUpperView"
         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" 
         xmlns:local="clr-namespace:project"
         xmlns:vm="clr-namespace:project.ViewModels"
         mc:Ignorable="d" 
         d:DesignHeight="100" d:DesignWidth="2200" FontFamily="Open Sans">
<UserControl.Resources>
    <vm:MainUpperViewModel  x:Key="MainUpperViewModel"/>
</UserControl.Resources>
<Grid DataContext="{Binding Source={StaticResource MainUpperViewModel}}">
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="1*" />
        <ColumnDefinition Width="1*" />
        <ColumnDefinition Width="1*" />
        <ColumnDefinition Width="1*" />
        <ColumnDefinition Width="1*" />
        <ColumnDefinition Width="1*" />
        <ColumnDefinition Width="1*" />
        <ColumnDefinition Width="1*" />
        <ColumnDefinition Width="1*" />
        <ColumnDefinition Width="1*" />
        <ColumnDefinition Width="1*" />
        <ColumnDefinition Width="1*" />
        <ColumnDefinition Width="1*" />
        <ColumnDefinition Width="1*" />
        <ColumnDefinition Width="1*" />
        <ColumnDefinition Width="1*" />
        <ColumnDefinition Width="1*" />
        <ColumnDefinition Width="1*" />
        <ColumnDefinition Width="1*" />
        <ColumnDefinition Width="1*" />
        <ColumnDefinition Width="1*" />
        <ColumnDefinition Width="1*" />
    </Grid.ColumnDefinitions>
    <Rectangle Grid.RowSpan="1" Grid.ColumnSpan="22" Fill="#013542"></Rectangle>
    <Label  Grid.Column="6" Grid.ColumnSpan="2" VerticalAlignment="Center" Foreground="White" FontSize="16">Balance:</Label>
    <Label x:Name="lblBalance" Grid.Column="7" Grid.ColumnSpan="5" VerticalAlignment="Center" Foreground="White" FontFamily="Open Sans SemiBold" FontSize="24" Margin="55,28,45,33">
        <Label.Content>
            <Binding Path="Balance"/>
        </Label.Content>
    </Label>
</Grid>

在设计器中，可以看到标签的内容

但是当我运行应用程序时，标签是空的

问题是什么？

我已经创建了一些 ViewModel，但我在那里使用的是文本框。我们使用了 INotifyPropertyChanged 接口(interface)，我不确定它是如何工作的，所以我的猜测是，它设置了内容，但不会显示它，因为标签没有更新，所以我尝试将 OnPropertyChanged 函数与PropertyChangedEventHandler，我们之前对其他 ViewModel 使用的，但它也不起作用，我不知道哪里出了问题。

最佳答案

有一些框架提供的类已经实现了所需的接口(interface)，如果你想自己做，这里有一种可能性:

首先你有你的 ViewModelBase 并且你所有的 ViewModels 都应该继承它

public abstract class ViewModelBase : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void RaisePropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    protected virtual bool SetAndRaisePropertyChanged<T>(ref T storage, T value, [CallerMemberName] string propertyName = "")
    {
        if (EqualityComparer<T>.Default.Equals(storage, value))
            return false;
        storage = value;
        this.RaisePropertyChanged(propertyName);
        return true;
    }
}

然后在您的 View 模型中，您将像这样声明您的属性:

private String _mBalance;
public String Balance
{
  get { return _mBalance; }
  set => SetAndRaisePropertyChanged(ref _mBalance, value);
}

[编辑]:我想保留答案的历史记录，因此请使用完整的功能示例检查下面的编辑:

通常我会拆分更多文件，但我想保持简单，所以你需要 2 个文件(我正在尝试应用 MVVM 模式，所以我正在添加目录): - View \MainWindow.xaml - ViewModels\MainWindowViewModel.cs

Views\MainWindow.xaml:

<Window x:Class="StackOverflow_DBG.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:StackOverflow_DBG"
        xmlns:viewmodels="clr-namespace:StackOverflow_DBG.ViewModels"
        mc:Ignorable="d"
        Title="MainWindow" Height="100" Width="400">
    <Window.DataContext>
        <viewmodels:MainWindowViewModel/>
    </Window.DataContext>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"/>
            <RowDefinition Height="auto"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*"/>
            <ColumnDefinition Width="*"/>
            <ColumnDefinition Width="*"/>
        </Grid.ColumnDefinitions>
        <Label Grid.Row="1" Grid.Column="0" Content="{Binding LabelTxt}" HorizontalAlignment="Center" VerticalAlignment="Center"/>
        <TextBox Grid.Row="1" Grid.Column="1" Text="{Binding ValueTxt}"/>
        <Button Grid.Row="1" Grid.Column="2" Content="Change Label" Command="{Binding ChangeLabel}"/>
    </Grid>
</Window>

ViewModels\MainWindowViewModel.cs:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Input;

namespace StackOverflow_DBG.ViewModels
{
    public abstract class ViewModelBase : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;

        protected virtual void RaisePropertyChanged([CallerMemberName] string propertyName = null)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }

        protected virtual bool SetAndRaisePropertyChanged<T>(ref T storage, T value, [CallerMemberName] string propertyName = "")
        {
            if (EqualityComparer<T>.Default.Equals(storage, value))
                return false;
            storage = value;
            this.RaisePropertyChanged(propertyName);
            return true;
        }
    }

    public class RelayCommand : ICommand
    {
        public event EventHandler CanExecuteChanged
        {
            add { CommandManager.RequerySuggested += value; }
            remove { CommandManager.RequerySuggested -= value; }
        }
        private Action methodToExecute;
        private Func<bool> canExecuteEvaluator;
        public RelayCommand(Action methodToExecute, Func<bool> canExecuteEvaluator)
        {
            this.methodToExecute = methodToExecute;
            this.canExecuteEvaluator = canExecuteEvaluator;
        }
        public RelayCommand(Action methodToExecute)
            : this(methodToExecute, null)
        {
        }
        public bool CanExecute(object parameter)
        {
            if (this.canExecuteEvaluator == null)
            {
                return true;
            }
            else
            {
                bool result = this.canExecuteEvaluator.Invoke();
                return result;
            }
        }
        public void Execute(object parameter)
        {
            this.methodToExecute.Invoke();
        }
    }

    class MainWindowViewModel : ViewModelBase
    {
        private String m_LabelTxt = "Foo";
        public String LabelTxt
        {
            get { return m_LabelTxt; }
            set => SetAndRaisePropertyChanged(ref m_LabelTxt, value);
        }

        private String m_ValueTxt;
        public String ValueTxt
        {
            get { return m_ValueTxt; }
            set => SetAndRaisePropertyChanged(ref m_ValueTxt, value);
        }

        private RelayCommand m_ChangeLabel;
        public RelayCommand ChangeLabel
        {
            get { return m_ChangeLabel; }
            set { m_ChangeLabel = value; }
        }

        public MainWindowViewModel()
        {
            ChangeLabel = new RelayCommand(() => {
                if (LabelTxt == "Foo")
                {
                    LabelTxt = "Bar ";
                }
                else
                {
                    LabelTxt = "Foo ";
                }
            });
        }
    }
}

通过这种方式，您还可以了解如何绑定(bind)按钮。按下按钮可以看到更新完成。如果使用与我相同的目录，请记住编辑 app.xaml 以使用 StartupUri="Views/MainWindow.xaml"> 而不是

StartupUri="MainWindow.xaml">

关于c# - 为什么不显示标签的内容？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/53324293/

c# - 为什么不显示标签的内容？

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