我正在构建一个iOS应用程序,我每隔几秒钟就会尝试更改一次背景图像。我使用以下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,我收到以下错误:
UIKit.UIKitThreadAccessException has been thrown
UIKit Consistency error: you are calling a UIKit method that can only
be invoked from the UI thread.
我不确定这意味着什么。
更新/编辑:(2017年7月23日)
以下问题解决了我的问题。我想循环图像,所以我做了一个随机生成器,但它只循环一次图像。
// 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);
});
}
答案 0 :(得分:3)
更新用户界面要求您在主线程(UI线程)上,将Background.Image
电话放在InvokeOnMainThread
内将解决UIKit
例外:
void ChangeBackground(Object state)
{
BackgroundTimer t = (BackgroundTimer)state;
t.counter++;
InvokeOnMainThread(() =>
{
Background.Image = UIImage.FromBundle("HydePark");
});
}
Xamarin有一个指南,概述了为什么/如何完成这些工作: