Xamarin Picker 查看无效选择 iOS 12

Question

下面是 Xamarin 文档中已经共享的示例代码。

 <Picker>
  <Picker.ItemsSource>
    <x:Array Type="{x:Type x:String}">
      <x:String>Baboon</x:String>
      <x:String>Capuchin Monkey</x:String>
      <x:String>Blue Monkey</x:String>
      <x:String>Squirrel Monkey</x:String>
      <x:String>Golden Lion Tamarin</x:String>
      <x:String>Howler Monkey</x:String>
      <x:String>Japanese Macaque</x:String>
    </x:Array>
  </Picker.ItemsSource>
</Picker>

当运行此代码在 iOS 12 模拟器中时，它可以工作，但是当您点击完成按钮时，selected 项目被更改并分配给列表中的第 4 项selected 项目。

例如，如果您 select 上面列表中的狒狒并点击完成按钮，select编辑的项目将更改为金狮面狨。

我不确定这个问题是否只与 iOS 12 有关。我正在下载以前版本的模拟器看看

我已经上传了模拟器的录像here，如果是OS相关问题或其他问题，谁能指导一下？

谢谢，

Answer 1

解决方法：如果还是不能解决问题，可以使用自定义渲染器，重写按钮的事件Done.

in iOS project

using System;
using Xamarin.Forms;
using Xamarin.Forms.Platform.iOS;
using UIKit;
using Foundation;
using ObjCRuntime;
using CoreGraphics;

[assembly: ExportRenderer(typeof(MyPicker), typeof(MyPickerRenderer))]
namespace xxx.iOS
{
  public class MyPickerRenderer:PickerRenderer,IUIPickerViewDelegate,IUIPickerViewDataSource
  {
    string SelectedValue;

    public MyPickerRenderer()
    {
    }

    public nint GetComponentCount(UIPickerView pickerView)
    {
        return 1;
    }

    public nint GetRowsInComponent(UIPickerView pickerView, nint component)
    {
        return Element.Items.Count;
    }

    [Export("pickerView:titleForRow:forComponent:")]
    public string GetTitle(UIPickerView pickerView, nint row, nint component)
    {
        return Element.Items[(int)row].ToString();
    }

    [Export("pickerView:didSelectRow:inComponent:")]
    public void Selected(UIPickerView pickerView, nint row, nint component)
    {
        Control.Text = Element.Items[(int)row];
        SelectedValue= Element.Items[(int)row]; 
    }

    protected override void OnElementChanged(ElementChangedEventArgs<Picker> e)
    {
        base.OnElementChanged(e);

        if(Control!=null)
        {
            SelectedValue = Element.Items[0];

            UIPickerView pickerView = (UIPickerView)Control.InputView;
            pickerView.WeakDelegate = this;
            pickerView.DataSource = this;


            UIToolbar toolbar = (UIToolbar)Control.InputAccessoryView;

            UIBarButtonItem done = new UIBarButtonItem("Done", UIBarButtonItemStyle.Done, (object sender, EventArgs click) =>
                {
                    Control.Text = SelectedValue;
                    toolbar.RemoveFromSuperview();
                    pickerView.RemoveFromSuperview();
                    Control.ResignFirstResponder();
                });
            toolbar.Items = new UIBarButtonItem[] { done };
        }

    }

  }
}

in forms

using System;
using Xamarin.Forms;
namespace app1
{
 public class MyPicker:Picker
 {
    public MyPicker()
    {
    }
 }
}

in xaml

 <local:MyPicker>               
  <local:MyPicker.ItemsSource>               
     <x:Array Type="{x:Type x:String}">                        
       <x:String>Baboon</x:String>
       <x:String>Capuchin Monkey</x:String>
       <x:String>Blue Monkey</x:String>
       <x:String>Squirrel Monkey</x:String>
       <x:String>Golden Lion Tamarin</x:String>
       <x:String>Howler Monkey</x:String>
       <x:String>Japanese Macaque</x:String>
     </x:Array>                    
   </local:MyPicker.ItemsSource>  
 </local:MyPicker>

Note: Here is a similar issue that you can refer

Answer 2

提到的解决方案here（清除模拟器内容）有效。

问题出在 Xcode 模拟器上，不确定是什么导致了这个问题。

Xamarin Picker 查看无效选择 iOS 12

Xamarin Picker View invalid selection iOS 12

ios

xamarin

xamarin.forms

xamarin.ios

ios12