.NET MAUI 7样式设置时出现调用目标抛出异常问题排查

问题场景 #

我自行开发了一个自定义控件，包含如下属性：

public TextAlignment HorizontalIconAlignment { get { return (TextAlignment)GetValue(HorizontalIconAlignmentProperty); } set { SetValue(HorizontalIconAlignmentProperty, value); } }
public static readonly BindableProperty HorizontalIconAlignmentProperty = BindableProperty.Create("HorizontalTextAlignment", typeof(TextAlignment), typeof(DuoToneIcon), TextAlignment.Start, propertyChanged: OnHorizontalIconAlignmentPropertyChanged);
private static void OnHorizontalIconAlignmentPropertyChanged(BindableObject bindable, object oldValue, object newValue)
{
    var control = (myControl)bindable;
    control.Label.HorizontalTextAlignment = (TextAlignment)newValue;
}

直接在控件上设置该属性时可正常使用：

<local:myControl Text="Something" HorizontalIconAlignment="Center" PrimaryColor="red" />

为避免重复设置，我将其加入Style.xaml的样式中：

<Style TargetType="local:myControl">
    <Setter Property="PrimaryColor" Value="{AppThemeBinding Light={StaticResource Primary}, Dark={StaticResource Gray900}}" />
</Style>

此时样式正常工作，但添加HorizontalIconAlignment设置后出现异常：

<Style TargetType="local:myControl">
    <Setter Property="PrimaryColor" Value="{AppThemeBinding Light={StaticResource Primary}, Dark={StaticResource Gray900}}" />
    <Setter Property="HorizontalIconAlignment" Value="Center" />
</Style>

异常信息：

Microsoft.Maui.Controls.Xaml.XamlParseException: 'Position 10:37. Type converter failed: Exception has been thrown by the target of an invocation.'
XmlInfo: Resources/Styles/Styles.xaml

问题原因及解决方案 #

你遇到的问题是依赖属性创建时的配置错误，具体有两处：

1. 依赖属性名称不匹配：BindableProperty.Create的第一个参数是依赖属性对应的CLR属性名称，你写的是"HorizontalTextAlignment"，但实际CLR属性名是HorizontalIconAlignment。样式系统会通过这个名称匹配依赖属性，名称不匹配会导致类型转换器无法正确解析属性，抛出异常。

2. 所有者类型错误：BindableProperty.Create的第三个参数是依赖属性所属的控件类型，你写的是typeof(DuoToneIcon)，但这个属性属于myControl，应该改为typeof(myControl)。

修正后的代码： #

public TextAlignment HorizontalIconAlignment { get { return (TextAlignment)GetValue(HorizontalIconAlignmentProperty); } set { SetValue(HorizontalIconAlignmentProperty, value); } }
public static readonly BindableProperty HorizontalIconAlignmentProperty = BindableProperty.Create(
    nameof(HorizontalIconAlignment), // 使用nameof避免硬编码错误
    typeof(TextAlignment), 
    typeof(myControl), 
    TextAlignment.Start, 
    propertyChanged: OnHorizontalIconAlignmentPropertyChanged);
private static void OnHorizontalIconAlignmentPropertyChanged(BindableObject bindable, object oldValue, object newValue)
{
    var control = (myControl)bindable;
    control.Label.HorizontalTextAlignment = (TextAlignment)newValue;
}

建议使用nameof(HorizontalIconAlignment)代替硬编码字符串，避免后续属性名修改时出现不一致问题。

内容的提问来源于stack exchange，提问作者Imran Sh