在Xamarin.iOS中实现TextLayer的垂直对齐

代码如下：

    public class SHLCTextLayer : CATextLayer {

        public SHLCTextLayer(IntPtr handle) : base(handle) {

        }

        public SHLCTextLayer() : base() {

        }

        public SHLCTextLayer(NSCoder coder) : base(coder) {

        }

        public SHLCTextLayer(NSObjectFlag t) : base(t) {

        }

        public override void DrawInContext(CGContext ctx) {
            try {
                var height = this.Bounds.Size.Height;
                var fontSize = this.FontSize;
                var yDiff = (height - fontSize) / 2 - fontSize / 10;

                ctx.SaveState();
                ctx.TranslateCTM((nfloat)0.0f, yDiff);
                base.DrawInContext(ctx);
                ctx.RestoreState();
            } catch (Exception e) {
                ErrorReporter.Report(e);
            }
        }

    }