iOS，Xamarin，UIView，Draw，动态动画不起作用

Question

I'm using MonoDevelop and xamarin for creating iOS application.

I have a view which looks like this:

public class MyView: UIView 
{
    private Timer _t = new Timer(1000);
    private int _i = 0;

    public MyView()
    {
        _t.Elapsed += (sender, e) => { 
             _i = (_i + 1) % 100;
             this.Draw(new Rectangle(0, 0, 110, 110)); 
         };
        _t.Enabled = true;
    }

    public override void Draw(RectangleF rect)
    {
        base.Draw(rect);
        var uiImage = UIImage.FromFile("myImage");
        var uiImageView = new UIIMageView(new Rectangle(_i, 0, 10, 10));
        uiImageView.Image = uiImage;
        AddSubView(uiIMageView);
    }
}

I expect that my image will move. But as a result I've only initial static image. Can anybody suggest approach how to do animation like described?

Answer 1

I would suggest modifying your code like so:

public MyView()
    {

        var uiImage = UIImage.FromFile("myImage");
        var uiImageView = new UIIMageView(new Rectangle(0, 0, 10, 10));
        uiImageView.Image = uiImage;
        AddSubView(uiIMageView);

        _t.Elapsed += (sender, e) => { 
             _i = (_i + 1) % 100;
             this.Draw(new Rectangle(_i, 0, 110, 110)); 
         };
        _t.Enabled = true;
    }

    public override void Draw(RectangleF rect)
    {
        base.Draw(rect);
        InvokeOnMainThread(()=>{
             uiImageView.Frame = rect;
        });
    }

I think part of your issue was that the timer Elapsed handler runs on a separate thread than the main UI Thread. Also you it'll be more efficient to not recreate the UIImageView each time.