x:bind 和数字字段的数据验证

Question

我在 UWP、x:Bind 和数据验证方面遇到了一些困难。我有一个非常简单的用例：我希望用户在 TextBox 中输入 int 并在用户离开 [=16] 时立即在 TextBlock 中显示数字=]. 我可以为 TextBox 设置 InputScope="Number"，但这不会阻止使用键盘键入字母字符（或粘贴某些内容）的人。问题是，当我用 Mode=TwoWay 绑定字段时，如果您绑定的字段声明为 似乎无法 阻止 System.ArgumentException =15=]。如果输入是数字，我想检查 set 方法，但异常发生在这之前。我的（非常简单的）ViewModel（这里没有模型，我尽量保持简单）：

public class MyViewModel : INotifyPropertyChanged
{
    private int _MyFieldToValidate;
    public int MyFieldToValidate
    {
        get { return _MyFieldToValidate; }
        set
        {
            this.Set(ref this._MyFieldToValidate, value);
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

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

    protected bool Set<T>(ref T storage, T value, [CallerMemberName]string propertyName = null)
    {
        if (Equals(storage, value))
        {
            return false;
        }
        else
        {
            storage = value;
            this.RaisedPropertyChanged(propertyName);
            return true;
        }
    }
}

我背后的代码：

public sealed partial class MainPage : Page
{
    public MyViewModel ViewModel { get; set; } = new MyViewModel() { MyFieldToValidate = 0 };

    public MainPage()
    {
        this.InitializeComponent();
    }
}

还有我的整个XAML:

<Page
    x:Class="SimpleFieldValidation.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:SimpleFieldValidation"
    xmlns:vm="using:SimpleFieldValidation.ViewModel"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">

    <Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
        <Grid.RowDefinitions>
            <RowDefinition Height="10*" />
            <RowDefinition Height="*" />
            <RowDefinition Height="10*" />
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*" />
            <ColumnDefinition Width="*" />
        </Grid.ColumnDefinitions>

        <TextBox Grid.Row="1" Grid.Column="0" Text="{x:Bind ViewModel.MyFieldToValidate, Mode=TwoWay}" x:Name="inputText" InputScope="Number" />
        <TextBlock Grid.Row="1" Grid.Column="1" Text="{x:Bind ViewModel.MyFieldToValidate, Mode=OneWay}" x:Name="textToDisplay" />
    </Grid>
</Page>

如果我在 TextBox 中键入一个数字字符，一切正常。但是，如果我键入一个 non-numeric 值（比如 "d"）（它甚至没有到达 MyFieldToValidate 的 set 方法的第一个括号处的断点）：

是否有最佳实践来做我想做的事？最简单的解决方案是首先阻止用户输入除数字以外的其他字符，但我一直在搜索数小时而没有找到简单的方法......另一种解决方案是在离开字段时验证数据，但我没有找到与 UWP 和 x:Bind 相关的东西（WPF 想的东西很少，但它们不能用 UWP 复制）。谢谢！

Answer 1

如@RTDev所说，你的异常是系统无法将string转int造成的

You can create a class that allows you to convert the format of your data between the source and the target by inheriting from IValueConverter.

You should always implement Convert(Object, TypeName, Object, String) with a functional implementation, but it's fairly common to implement ConvertBack(Object, TypeName, Object, String) so that it reports a not-implemented exception. You only need a ConvertBack(Object, TypeName, Object, String) method in your converter if you are using the converter for two-way bindings, or using XAML for serialization.

有关详细信息，请参阅 IValueConverter Interface。

例如：

<Page.Resources>
    <local:IntFormatter x:Key="IntConverter" />
</Page.Resources>
<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
    <Grid.RowDefinitions>
        <RowDefinition Height="10*" />
        <RowDefinition Height="*" />
        <RowDefinition Height="10*" />
    </Grid.RowDefinitions>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="*" />
        <ColumnDefinition Width="*" />
    </Grid.ColumnDefinitions>
    <TextBox Grid.Row="1" Grid.Column="0" Text="{x:Bind ViewModel.MyFieldToValidate, Mode=TwoWay,Converter={StaticResource IntConverter}}" x:Name="inputText" InputScope="Number" />
    <TextBlock Grid.Row="1" Grid.Column="1" Text="{x:Bind ViewModel.MyFieldToValidate, Mode=OneWay}" x:Name="textToDisplay" />
</Grid>

IntFormatter class:

internal class IntFormatter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, string language)
    {
        if (value != null)
        {
            return value.ToString();
        }
        else
        {
            return null;
        }
    }

    public object ConvertBack(object value, Type targetType, object parameter, string language)
    {
        int n;
        bool isNumeric = int.TryParse(value.ToString(), out n);
        if (isNumeric)
        {
            return n;
        }
        else
        {
            return 0;
        }
    }
}

Answer 2

如果您不希望用户键入字母数字字符，我认为最优雅的解决方案是创建一个新的 class NumberBox 继承自 class InputBox 并重载 OnKeyDown 方法来拦截字母数字击键，像这样：

using Windows.System;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Input;

namespace MyProject.Controls
{
    public sealed class NumberBox : TextBox
    {
        protected override void OnKeyDown(KeyRoutedEventArgs e)
        {
            if (e.Key >= VirtualKey.Number0 && e.Key <= VirtualKey.Number9 ||
                e.Key >= VirtualKey.NumberPad0 && e.Key <= VirtualKey.NumberPad9 ||
                e.Key >= VirtualKey.Left && e.Key <= VirtualKey.Down ||
                e.Key == VirtualKey.Delete ||
                e.Key == VirtualKey.Tab ||
                e.Key == VirtualKey.Back ||
                e.Key == VirtualKey.Enter)
                base.OnKeyDown(e);
            else
                e.Handled = true;
        }
    }
}

然后在你的XAML中添加一个命名空间来引用你的NumberBoxclass所在的命名空间，然后替换InputBox 与 control:NumberBox，像这样：

<Page
    x:Class="MyProject.View.CalibrarEnfoque"
    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:local="using:MyProject.View"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:controls="using:MyProject.Controls"
    mc:Ignorable="d">
    <Grid>
        <controls:NumberBox Text="{x:Bind ViewModel.MyValue, Mode=TwoWay}"/>
    </Grid>
</Page>

x:bind 和数字字段的数据验证

x:bind and data validation for numeric field

validation

uwp

xbind