Question

我在iOS中有一个需要以两种模式显示的视图，一种在导航标题中有一个关闭按钮，另一种没有关闭按钮。我在viewmodel中添加了一个bool来处理这个问题。但是，UIBarButtonItem在我的viewmodel中没有绑定到此bool的Hidden属性。有关如何解决此问题的任何建议？注意：我不需要在运行时更改此关闭按钮的可见性。这只是在显示视图之前我需要的初始只读设置。

Answer 1

对于静态设置，您只需尝试检查ViewDidLoad代码中的viewmodel属性。

有关创建自定义绑定的信息，请参阅https://speakerdeck.com/cirrious/custom-bindings-in-mvvmcross

Answer 2

我遇到了同样的问题，但需要动态更改。通过禁用按钮并将色调颜色设置为清除，我能够模拟可见性。

创建自定义TargetBinding：

/// <summary>
/// Hides a UIBarButtonItem by disabling and setting the TintColor to Clear
/// </summary>
public class UIBarButtonItemVisibilityTargetBinding : MvxConvertingTargetBinding
{
    protected UIBarButtonItem Button => base.Target as UIBarButtonItem;

    private readonly UIColor _tintColor;

    public UIBarButtonItemVisibilityTargetBinding(UIBarButtonItem button) : base(button)
    {
        this._tintColor = button.TintColor;

        if (button == null) {
            MvxBindingTrace.Trace(MvxTraceLevel.Error, "Error - UIBarButtonItem is null in UIBarButtonItemVisibilityTargetBinding");
        }
    }

    public override MvxBindingMode DefaultMode => MvxBindingMode.OneWay;

    public override System.Type TargetType => typeof(bool);

    protected override void SetValueImpl(object target, object value)
    {
        var button = (UIBarButtonItem) target;
        var enabled = (bool) value;

        button.Enabled = enabled;
        button.TintColor = enabled ? _tintColor : UIColor.Clear;
    }
}

在设置文件中注册TargetBinding：

    protected override void FillTargetFactories (MvvmCross.Binding.Bindings.Target.Construction.IMvxTargetBindingFactoryRegistry registry)
    {
        base.FillTargetFactories (registry);

        registry.RegisterCustomBindingFactory<UIBarButtonItem> ("Visibility", button => new UIBarButtonItemVisibilityTargetBinding (button));

    }

使用自定义绑定绑定到视图控制器中的按钮：

set.Bind (btnBarItem).For("Visibility").To (vm => vm.ShowButton);

MvvmCross：如何绑定到UIBarButtonItem的可见性？

2 个答案: