Transitions¶

组件的Transitions属性无法设置为BrushTransition类型，导致NullReferenceException异常。

错误信息

System.NullReferenceException: 'Object reference not set to an instance of an object.'

MainWindow.xaml

<Border Name="xyz">
    <Border.Transitions>
        <BrushTransition Property="Background" Duration="5" />
    </Border.Transitions>
</Border>

组件的 Transitions 设置为 BrushTransition 类型，调试模式下出现 NullReferenceException 异常

解决方案¶

MainWindow.xaml

    <Border Name="xyz">
        <Border.Transitions>
++          <Transitions>
                <BrushTransition Property="Background" Duration="5" />
++          </Transitions>
        </Border.Transitions>
    </Border>

为什么¶

Transitions属性的类型是Transitions，而不是BrushTransition。Transitions是一个集合，可以包含多个过渡效果。

Transitions.cs

public sealed class Transitions : AvaloniaList<ITransition>, IAvaloniaListItemValidator<ITransition>
{
    ...
}

BrushTransition.cs

public class BrushTransition : Transition<IBrush?>
{
    ...
}

查看源码可以发现，一个是集合，一个是集合元素。 Cannot implicitly convert type 'Avalonia.Animation.BrushTransition' to 'Avalonia.Animation.Transitions'