当聚焦时改变颜色

Question

我想在聚焦文本框时改变颜色，但是
我收到此错误：

  

'UIView.Focused'不能分配给它-只读

public UITextField text;
 UITextField.Focused += OnFocused 

    private void OnFocused(object sender, FocusEventArgs focusEventArgs) {

  }

Answer 1

您可以使用以下AttachProperty：

 public static class Attach
{
    public static BindableProperty IsFocusedProperty = BindableProperty.Create("IsFocused", typeof(bool), typeof(Attach), false, propertyChanged: OnIsFocusedChanged);

    public static void OnIsFocusedChanged(BindableObject bindable, object oldValue, object newValue)
    {
        var textField = bindable as UITextField;
        if(newValue) textField.Focus();
    }
}

Answer 2

您可以使用started和ended：

                (view as UITextField).Started += focus;
                (view as UITextField).Ended += unfocus;

和代表将是：

public static void focus(object sender, EventArgs e)
        {
            var native = (UITextField)sender;
            native.Layer.MasksToBounds = true;
            native.Layer.BorderColor = ColorPalette.LightBlue.CGColor;
            native.BorderStyle = UITextBorderStyle.RoundedRect;
            native.Layer.BorderWidth = 2;
        }

        public static void unfocus(object sender, EventArgs e)
        {
            var native = (UITextField)sender;
            native.Layer.MasksToBounds = true;
            native.Layer.BorderWidth = (System.nfloat)0;
        }

Answer 3

关于 UIView.Focused Property ：public virtual bool Focused { get; }仅具有get方法，因此不能使用UITextField.Focused += OnFocused，并且会转回错误：'UIView.Focused' cannot be assigned to -- it is read only

如果要在TextField开始编辑时调用该方法，则可以使用started/ended来引用x-rw的答案。但是您需要知道此方法来自Xamarin Forms。

在本机iOS中，有一种Delegate方法可用于了解 UITextField 是否要聚焦。

mtTextField.EditingDidBegin += MtTextField_EditingDidBegin;
mtTextField.EditingDidEnd += MtTextField_EditingDidEnd;

private void MtTextField_EditingDidEnd(object sender, EventArgs e)
{
    mtTextField.TextColor = UIColor.Gray;
}

private void MtTextField_EditingDidBegin(object sender, EventArgs e)
{
    mtTextField.TextColor = UIColor.Blue;
}

效果：

注意：

您还可以发现，即使正在编辑UITextField，属性UITextField.Focused始终都是False。因此，建议不要使用Focused来检查UITextField是否开始编辑。