Question

我正在尝试绑定到TabBarItem的徽章值，如下所示：

var set = this.CreateBindingSet<MyView, MyViewModel>();
set.Bind(ViewControllers[0].TabBarItem.BadgeValue).To(vm => vm.MyNumber);
set.Apply();

但是我收到以下错误：

MvxBind: Error:   6.30 Empty binding target passed to MvxTargetBindingFactoryRegistry

但是，如果我像这样直接设置值，则会出现徽章：

ViewControllers[0].TabBarItem.BadgeValue = ((MyViewModel)ViewModel).MyNumber;

为什么绑定不起作用？谢谢！

Answer 1

这不起作用，因为如果您要绑定的内容已经作为有效的绑定目标存在，则需要设置自己的绑定扩展。

看看here Stuart为Android回答类似的问题。

Answer 2

创建自定义绑定：

public class TabBadgeBinding : MvxTargetBinding
{
    public const string TargetPropertyName = nameof(TabBadgeBinding);

    private readonly UIViewController _viewController;

    public TabBadgeBinding(UIViewController viewController) : base(viewController)
    {
        _viewController = viewController;
    }

    public override Type TargetType => typeof(UIViewController);

    public override MvxBindingMode DefaultMode => MvxBindingMode.OneWay;

    public override void SetValue(object value)
    {
        if (value is string badgeValue)
        {
            _viewController.TabBarItem.BadgeValue = badgeValue;
        }
    }
}

在Setup.cs中注册绑定：

    protected override void FillTargetFactories(IMvxTargetBindingFactoryRegistry registry)
    {
        base.FillTargetFactories(registry);
        registry.RegisterFactory(new MvxCustomBindingFactory<UIViewController>(TabBadgeBinding.TargetPropertyName, (controller) => new TabBadgeBinding(controller)));
    }

在您的VC中使用绑定：

    set.Bind(ParentViewController).For(TabBadgeBinding.TargetPropertyName).To(vm => vm.UnreadNotificationsCount);

MVVMCross绑定到badgevalue

2 个答案: