MAUI新生2.2-数据绑定和MVVM：数据绑定转换器Converter

namespace MauiApp8.Converters;

public class IntToBoolConverter : IValueConverter
{
    //Convert方法中的value参数，为绑定源数据，此例中为int类型
    //如果value为0，则返回false，否则返回true
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return (int)value != 0;
    }
    //ConvertBack方法的value参数，为绑定目标数据，此例中为bool类型
    //如果value为true，则返回1，否则返回0
    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return (bool)value ? 1 : 0;
    }
}

<ContentPage
    x:Class="MauiApp8.MainPage"
    xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
    xmlns:converter="clr-namespace:MauiApp8.Converters">
    <!--通过 xmlns:converter 引入转换器命名空间-->
    <!--在页面级资源字典中，创建转换器对象，字典键名为intToBool-->
    <ContentPage.Resources>
        <converter:IntToBoolConverter x:Key="intToBool" />
    </ContentPage.Resources>

    <StackLayout Padding="30">
        <Entry x:Name="entry1" Text="" Placeholder="请输入" />

        <!--Binding中，通过使用Converter，绑定转换器对象-->
        <Button
            x:Name="button1"
            IsEnabled="{Binding Source={x:Reference entry1}, Path=Text.Length, Converter={StaticResource intToBool}}"
            Text="确定" />

    </StackLayout>
</ContentPage>

public class IntToMultipleConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        //转换value为整数，如果无法转换，则使用默认值0
        int valueInt = 0;
        int.TryParse(value.ToString(), out valueInt);

        //转换parameter为整数，如果无法转换，则使用默认值1
        int parameterInt = 1;
        int.TryParse(parameter.ToString(),out parameterInt);

        return valueInt * parameterInt;
    }
    //绑定模式为OneWay，不需要定义ConverBack方法
    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

<ContentPage
    ...
    xmlns:converter="clr-namespace:MauiApp8.Converters">

    <ContentPage.Resources>
        <converter:IntToMultipleConverter x:Key="intToMultiple" />
    </ContentPage.Resources>

    <StackLayout Padding="30">
        <Entry x:Name="entry1" Text="" Keyboard="Numeric" Placeholder="请输入数据" />
        <!--通过ConverterParameter向转换器传入参数-->
        <Label x:Name="label1" Text="{Binding Source={x:Reference entry1}, 
                                              Path=Text, 
                                              Converter={StaticResource intToMultiple}, 
                                              ConverterParameter=5}" />
    </StackLayout>

</ContentPage>

//布尔类型和泛型类型之间的转换
public class BoolToObjectConverter<T> : IValueConverter
{
    //定义两个泛型属性，Bool值为true时，与TrueObject相互转换；为false时，与FalseObject相互转换
    public T TrueObject { get; set; }
    public T FalseObject { get; set; }
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return (bool)value ? TrueObject : FalseObject;
    }
    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        //绑定目标转为泛型T，并与TrueObject比如，如相等则返回true，否则返回false
        return ((T)value).Equals(TrueObject);
    }
}

<ContentPage
    ......
    xmlns:converter="clr-namespace:MauiApp8.Converters">

    <StackLayout Padding="30">
        <Switch x:Name="switch1" /> <!--Label文本开关-->
        <Switch x:Name="switch2" /> <!--Label文本颜色开关-->
        <Label>
            <Label.Text>
                <Binding Source="{x:Reference switch1}" Path="IsToggled">
                    <Binding.Converter>
                        <converter:BoolToObjectConverter x:TypeArguments="x:String" TrueObject="Yes" FalseObject="No"/>
                    </Binding.Converter>
                </Binding>
            </Label.Text>
            <Label.TextColor>
                <Binding Source="{x:Reference switch2}" Path="IsToggled">
                    <Binding.Converter>
                        <converter:BoolToObjectConverter x:TypeArguments="Color" TrueObject="Green" FalseObject="Red"/>
                    </Binding.Converter>
                </Binding>
            </Label.TextColor>
        </Label>
    </StackLayout>

</ContentPage>