c# - Xamarin IOS 基于自定义渲染器中的 IsFocused 属性隐藏搜索栏图标

Question

我想使用基于 IsFocused 属性的自定义 SearchBarRenderer 在 IOS 中隐藏搜索栏图标。我怎样才能做到这一点？

protected override void OnElementPropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
        {
            base.OnElementPropertyChanged(sender, e);

            if (Element == null || Control == null)
                return;

            var element = Element as CustomSearchBar;

            if (element.IsFocused)
            {

            }
            else
            {

            }
        }

Answer 1

如果你使用Custom Renderer来实现它，代码如下。

[assembly: ExportRenderer(typeof(CustomSearchBar), typeof(CustomSearchBarRenderer))]
namespace App15.iOS
{
    public class CustomSearchBarRenderer : SearchBarRenderer
    {
        UIImage searchImg;
        protected override void OnElementChanged(ElementChangedEventArgs<SearchBar> e)
        {
            base.OnElementChanged(e);
            searchImg = Control.GetImageForSearchBarIcon(UISearchBarIcon.Search, UIControlState.Normal);
            if (e.OldElement != null)
            {
                Control.OnEditingStarted -= Control_OnEditingStarted;
                Control.OnEditingStopped -= Control_OnEditingStopped;
            }

            if (e.NewElement != null)
            {
                if (null != Control)
                {
                    Control.OnEditingStarted += Control_OnEditingStarted;
                    Control.OnEditingStopped += Control_OnEditingStopped;
                }
            }
        }

        private void Control_OnEditingStopped(object sender, EventArgs e)
        {
            var searchBar = sender as UISearchBar;
            searchBar.SetImageforSearchBarIcon(searchImg, UISearchBarIcon.Search, UIControlState.Normal);
        }

        private void Control_OnEditingStarted(object sender, EventArgs e)
        {
            var searchBar = sender as UISearchBar;
            searchBar.SetImageforSearchBarIcon(new UIImage(), UISearchBarIcon.Search, UIControlState.Normal);
        }
    }
}

注意:App15 是我本地项目中的命名空间。

作为文档 Introduction to Effects 的效果说，你也可以引用这个文档Creating an Effect使用 Effect 来实现它，因为它不需要使用 Custom Renderer 来实现它。

效果示例如下:

创建SearchBarEffects:

public class SearchBarEffects : RoutingEffect
{
    public SearchBarEffects() : base($"MyCompany.{nameof(SearchBarEffects)}")
    {

    }
}

在 Xaml 中使用:

// here is custom renderer
<local:CustomSearchBar Placeholder="renderer input"/> 
// here is custom effect
<SearchBar Placeholder="effect input">
    <SearchBar.Effects>
        <local:SearchBarEffects />
    </SearchBar.Effects>
</SearchBar>

在 iOS 解决方案中创建 SearchBarEffect:

[assembly: ResolutionGroupName("MyCompany")]
[assembly: ExportEffect(typeof(App15.iOS.SearchBarEffect), "SearchBarEffects")]
namespace App15.iOS
{
    public class SearchBarEffect : PlatformEffect
    {
        UIImage searchImg;
        protected override void OnAttached()
        {
            searchImg = ((UISearchBar)Control).GetImageForSearchBarIcon(UISearchBarIcon.Search, UIControlState.Normal);
            ((UISearchBar)Control).OnEditingStarted += SearchBar_OnEditingStarted;
            ((UISearchBar)Control).OnEditingStopped += SearchBar_OnEditingStopped;
        }

        private void SearchBar_OnEditingStopped(object sender, EventArgs e)
        {
            var searchBar = sender as UISearchBar;
            searchBar.SetImageforSearchBarIcon(searchImg, UISearchBarIcon.Search, UIControlState.Normal);
        }

        private void SearchBar_OnEditingStarted(object sender, EventArgs e)
        {
            var searchBar = sender as UISearchBar;
            searchBar.SetImageforSearchBarIcon(new UIImage(), UISearchBarIcon.Search, UIControlState.Normal);
        }

        protected override void OnDetached()
        {
            ((UISearchBar)Control).OnEditingStarted -= SearchBar_OnEditingStarted;
            ((UISearchBar)Control).OnEditingStopped -= SearchBar_OnEditingStopped;
        }
    }
}

最后，通过两种方式展示效果。向上是 Effect 的，向下是 Renderer 的。