问题描述
这是我的 IOS iPad 页面我想显示下拉菜单,请帮助我如何编写代码, 我为此使用了选择器,但菜单项显示在底部,我如何解决此问题
解决方法
这是一种通过“控件组合”实现这种“下拉”的解决方法。
首先,在视图上添加一个 UITextField 来显示选中的项目。
UITextField _dropTextField;
UIView _dropDownView;
UIPickerView _pickerView;
public override void ViewDidLoad()
{
base.ViewDidLoad();
// Perform any additional setup after loading the view,typically from a nib.
this.View.BackgroundColor = UIColor.White;
// add textfield
_dropTextField = new UITextField();
_dropTextField.Frame = new CGRect(100,100,300,30);
_dropTextField.BackgroundColor = UIColor.Gray;
this.View.AddSubview(_dropTextField);
// call CreateDropDownView
CreateDropDownView();
}
其次,定义一个方法来创建一个自定义的 UIView 持有一个 UIPickerView。
// create a custom UIView to show pickView
private void CreateDropDownView()
{
_dropDownView = new UIView(new CGRect(_dropTextField.Frame.X,_dropTextField.Frame.Y,_dropTextField.Frame.Width,300));
_dropTextField.Delegate = this;
_pickerView = new UIPickerView();
_pickerView.Frame = new CGRect(_dropTextField.Bounds.X,_dropTextField.Bounds.Y + _dropTextField.Frame.Height,300);
PeopleModel pickerModel = new PeopleModel(_dropTextField,_dropDownView);
_pickerView.Model = pickerModel;
_dropDownView.AddSubview(_pickerView);
}
然后,要在 TextField 聚焦时显示 UIView,还需要实现接口 IUITextFieldDelegate
。
// show pickerview
[Export("textFieldShouldBeginEditing:")]
public bool ShouldBeginEditing(UITextField textField)
{
View.AddSubview(_dropDownView);
UIApplication.SharedApplication.KeyWindow.BringSubviewToFront(_pickerView);
return false;
}
以上代码中的PeopleModel
请参考本documentation中的“class PeopleModel”。此外,您需要覆盖其中的一些方法。
private UITextField dropTextField;
private UIView dropDownView;
public PeopleModel(UITextField dropTextField,UIView dropDownView)
{
this.dropDownView = dropDownView;
this.dropTextField = dropTextField;
}
public override nint GetComponentCount(UIPickerView pickerView)
{
return 1;
}
// ...
public override void Selected(UIPickerView pickerView,nint row,nint component)
{
dropDownView.RemoveFromSuperview();
dropTextField.Text = $"{names[pickerView.SelectedRowInComponent(0)]}";
}
// ...