UIButton 未在 UIView Xamarin 中显示

Question

我遵循了 Xamarin 食谱之一（可在此处找到：http://docs.xamarin.com/recipes/ios/standard_controls/popovers/display_a_loading_message），但我不想使用活动微调器，而是想添加一个 UIButton。我替换了活动微调器并留下了以下 UIView 类，但是当我加载视图时，按钮没有加载/可见，但是我添加的标签是可见的。有什么想法吗？

源代码：

public class testOverlay : UIView {

    UIButton buttonRect;
    UILabel testLabel;

    public testOverlay (RectangleF frame) : base (frame)
    {
        // configurable bits
        BackgroundColor = UIColor.Black;
        Alpha = 0.75f;
        AutoresizingMask = UIViewAutoresizing.FlexibleDimensions;

        float labelHeight = 22;
        float labelWidth = Frame.Width - 20;

        // derive the center x and y
        float centerX = Frame.Width / 2;
        float centerY = Frame.Height / 2;

        // create the activity spinner, center it horizontall and put it 5     points above center x
        buttonRect = UIButton.FromType(UIButtonType.RoundedRect);
        buttonRect.SetTitle ("Confirm", UIControlState.Normal);
                    buttonRect.Frame = new RectangleF (
            centerX - (buttonRect.Frame.Width / 2) ,
            centerY - buttonRect.Frame.Height - 20 ,
            buttonRect.Frame.Width ,
            buttonRect.Frame.Height);
        buttonRect.AutoresizingMask = UIViewAutoresizing.FlexibleMargins;
        AddSubview (buttonRect);

        // create and configure the "Loading Data" label
        testLabel = new UILabel(new RectangleF (
            centerX - (labelWidth / 2),
            centerY + 20 ,
            labelWidth ,
            labelHeight
            ));
        testLabel.BackgroundColor = UIColor.Clear;
        testLabel.TextColor = UIColor.White;
        testLabel.Text = "Loading...";
        testLabel.AutoresizingMask = UIViewAutoresizing.FlexibleMargins;
        AddSubview (testLabel);
    }

    /// <summary>
    /// Fades out the control and then removes it from the super view
    /// </summary>
    public void Hide ()
    {
        UIView.Animate (
            0.5, // duration
            () => { Alpha = 0; },
        () => { RemoveFromSuperview(); }
        );
    }
};

谢谢

Answer 1

您的问题出在这部分代码中：

buttonRect.Frame = new RectangleF (
    centerX - (buttonRect.Frame.Width / 2) ,
    centerY - buttonRect.Frame.Height - 20 ,
    buttonRect.Frame.Width ,
    buttonRect.Frame.Height);

您正在设置按钮框架的 x、y、宽度和高度，然后才设置它。

将代码改成这样可以解决问题：

var buttonWidth = 100;
var buttonHeight = 50;
buttonRect.Frame = new RectangleF (
    centerX - buttonWidth / 2 ,
    centerY - buttonHeight - 20 ,
    buttonWidth ,
    buttonHeight);

Answer 2

您已经为您的 UILabel 指定了一个框架，但没有为您的 UIButton。您必须指定一个框架来确定元素将出现在视图中的哪个位置。