Xamarin Forms选择器“确定”或“取消”按钮按下检测

Question

我正在使用Xamarin Forms开发应用程序，遇到了Picker组件的一些问题。

在选择完Picker后，我需要确定用户是否按下了“确定”或“取消”按钮。

我尝试使用Focus和Unfocus，但这并不能帮助我确定哪个用户按下了“确定”或“取消”按钮。

- Mustafa

---

建议您创建一个自定义渲染器，然后创建本地处理程序，以在这些事件触发时通知您。 - FreakyAli

我该如何在这个主题上使用自定义渲染器？我需要在iOS和Android上使用它。我无法使用自定义渲染器捕获OK或Cancel按钮的点击事件。 - Mustafa

你可以检查我的答案。如果我的回答有帮助，请不要忘记标记它，这样更多的人就会看到它。 - Lucas Zhang

Answer 1

解决方法：

您应该在CustomRenderer中重写Picker的工具栏。

iOS

[assembly:ExportRenderer(typeof(Picker),typeof(MyPickerRenderer))]
namespace App6.iOS
{
  public class MyPickerRenderer:PickerRenderer
  {
    public MyPickerRenderer()
    {

    }



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

        if(Control!=null)
        {



            UIPickerView pickerView = (UIPickerView)Control.InputView;


            // get the button Done and rewrite the event
            UIToolbar toolbar = (UIToolbar)Control.InputAccessoryView;

            UIBarButtonItem done = new UIBarButtonItem("OK", UIBarButtonItemStyle.Done, (object sender, EventArgs click) =>
            {

                MessagingCenter.Send<Object>(this,"Ok_Clicked");

            });

            UIBarButtonItem cancel = new UIBarButtonItem(UIBarButtonSystemItem.Cancel, (object sender, EventArgs click) =>
            {

                MessagingCenter.Send<Object>(this, "Cancel_Clicked");
            });


            UIBarButtonItem empty = new UIBarButtonItem(UIBarButtonSystemItem.FlexibleSpace, null);

            toolbar.Items = new UIBarButtonItem[] { cancel,empty, done };
        }

    }
  }
}

安卓操作系统

[assembly: ExportRenderer(typeof(Picker), typeof(MyPickerRenderer))]
namespace App6.Droid
{
  public class MyPickerRenderer : PickerRenderer
  {
    IElementController ElementController => Element as IElementController;

    public MyPickerRenderer(Context context) : base(context)
    {

    }


    private AlertDialog _dialog;

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

        if (e.NewElement == null || e.OldElement != null)
            return;

        Control.Click += Control_Click;
    }

    protected override void Dispose(bool disposing)
    {
        Control.Click -= Control_Click;
        base.Dispose(disposing);
    }




    private void Control_Click(object sender, EventArgs e)
    {

        Picker model = Element;

        var picker = new NumberPicker(Context);
        if (model.Items != null && model.Items.Any())
        {

            picker.MaxValue = model.Items.Count - 1;
            picker.MinValue = 0;

            picker.SetDisplayedValues(model.Items.ToArray());

            picker.WrapSelectorWheel = false;
            picker.Value = model.SelectedIndex;
        }

        var layout = new LinearLayout(Context) { Orientation = Orientation.Vertical };
        layout.AddView(picker);

        ElementController.SetValueFromRenderer(VisualElement.IsFocusedProperty, true);

        var builder = new AlertDialog.Builder(Context);
        builder.SetView(layout);

        builder.SetTitle(model.Title ?? "");
        builder.SetNegativeButton("Cancel  ", (s, a) =>
        {
            MessagingCenter.Send<Object>(this, "Cancel_Clicked");
        });
        builder.SetPositiveButton("Ok ", (s, a) =>
        {
            ElementController.SetValueFromRenderer(Picker.SelectedIndexProperty, picker.Value);
            // It is possible for the Content of the Page to be changed on SelectedIndexChanged.
            // In this case, the Element & Control will no longer exist.
            if (Element != null)
            {
                if (model.Items.Count > 0 && Element.SelectedIndex >= 0)
                    Control.Text = model.Items[Element.SelectedIndex];
                ElementController.SetValueFromRenderer(VisualElement.IsFocusedProperty, false);
                // It is also possible for the Content of the Page to be changed when Focus is changed.
                // In this case, we'll lose our Control.

            }
            MessagingCenter.Send<Object>(this, "Ok_Clicked");
        });

        _dialog = builder.Create();
        _dialog.DismissEvent += (ssender, args) =>
        {
            ElementController?.SetValueFromRenderer(VisualElement.IsFocusedProperty, false);
        };
        _dialog.Show();
    }

  }
}

您可以使用MessagingCenter在表单中处理事件。

在ContentPage中实现

public MainPage()
{
   InitializeComponent();

   MessagingCenter.Subscribe<Object>(this, "Ok_Clicked", (sender)=> {

      picker.Unfocus();

      DisplayAlert("Title", "Ok has been clicked", "cancel");

      //do something you want

   });

   MessagingCenter.Subscribe<Object>(this, "Cancel_Clicked", (sender) => {

       picker.Unfocus();

       DisplayAlert("Title", "Cancel has been clicked", "cancel");

       //do something you want
     });

 }

- Lucas Zhang