在iOS iOS Xamarin上更改背景

我正在构build一个iOS应用程序，我试图每隔几秒更改背景图片。 我使用这里的代码设置了一个计时器： https ： //developer.xamarin.com/api/type/System.Threading.Timer/

我的代码如下所示：

using System; using System.Threading; using UIKit; namespace TestApp { public partial class ViewController : UIViewController { // New Timer class BackgroundTimer { public int counter = 0; public Timer tmr; } // Load screen public override void ViewDidLoad() { base.ViewDidLoad(); BackgroundTimer s = new BackgroundTimer(); // Create the delegate that invokes methods for the timer. TimerCallback timerDelegate = new TimerCallback(ChangeBackground); // Create a timer that waits three seconds, then invokes every three seconds. Timer timer = new Timer(timerDelegate, s, 3000, 3000); // Keep a handle to the timer, so it can be disposed. s.tmr = timer; void ChangeBackground(Object state) { BackgroundTimer t = (BackgroundTimer)state; t.counter++; Background.Image = UIImage.FromBundle("HydePark"); } 

当我在模拟器中运行它时，出现以下错误：

 UIKit.UIKitThreadAccessException has been thrown UIKit Consistency error: you are calling a UIKit method that can only be invoked from the UI thread. 

我不确定这是什么意思。

更新/编辑：（2017年7月23日）

下面的问题解决了我的问题。 我想循环图像，所以我做了一个随机的发生器，但它只循环一次的图像。

  // Load screen public override void ViewDidLoad() { base.ViewDidLoad(); // Random number generator Random RandomImage = new Random(); int RandomImg = RandomImage.Next(1, 6); string image = ""; // Switch statement for displaying different messages switch (RandomImg) { case 1: image = "Image1"; break; case 2: image = "Image2"; break; case 3: image = "Image3"; break; case 4: image = "Image4"; break; case 5: image = "Image5"; break; } BackgroundTimer s = new BackgroundTimer(); // Create the delegate that invokes methods for the timer. TimerCallback timerDelegate = new TimerCallback(ChangeBackground); // Create a timer that waits three seconds, then invokes every three seconds. Timer timer = new Timer(timerDelegate, s, 3000, 3000); // Keep a handle to the timer, so it can be disposed. s.tmr = timer; void ChangeBackground(Object state) { BackgroundTimer t = (BackgroundTimer)state; t.counter++; InvokeOnMainThread(() => { Background.Image = UIImage.FromBundle(image); }); } 

Answer 1

更新用户界面要求您在主线程（UI线程）上，将Background.Image调用放在InvokeOnMainThread将解决UIKitexception：

 void ChangeBackground(Object state) { BackgroundTimer t = (BackgroundTimer)state; t.counter++; InvokeOnMainThread(() => { Background.Image = UIImage.FromBundle("HydePark"); }); } 

Xamarin提供了一个指南，概述了为什么/如何完成这些工作：

• https://developer.xamarin.com/guides/ios/user_interface/ios-ui/ui-thread/