C# 如何正确地取消订阅活动
如何才能正确地取消订阅事件,并确保现在未调用调用的方法 我的问题是这种代码:C# 如何正确地取消订阅活动,c#,C#,如何才能正确地取消订阅事件,并确保现在未调用调用的方法 我的问题是这种代码: public class MyClassWithEvent { public event EventHandler MyEvent; public int Field; } public class MyMainClass { private MyClassWithEvent myClass; public void Start() { myClass.MyE
public class MyClassWithEvent
{
public event EventHandler MyEvent;
public int Field;
}
public class MyMainClass
{
private MyClassWithEvent myClass;
public void Start()
{
myClass.MyEvent += new EventHandler(doSomething);
}
public void Stop()
{
myClass.MyEvent -= new EventHandler(doSomething);
myClass = null;
}
private void doSomething()
{
myClass.Field = 42;
}
}
如果在执行doSomething
时调用了myClass=null
,则指令myClass.Field=42
会引发错误,因为myClass为null
在设置myClass=null
之前,如何确保没有执行doSomething
编辑:
其他例子:
public void Stop()
{
myClass.MyEvent -= new EventHandler(doSomething);
// Can I add a function here to be sure that doSomething is not running ?
myClass.Field = 101;
}
在这种情况下,我不确定myClass.Field
是42还是101
Edit2:
显然我的问题不像我想的那么简单。我将解释我的确切情况
我的代码是:
public class MyMainClass
{
object camera;//can be type uEye.Camera or DirectShowCamera
bool isRunning = false;
public void Start()
{
if (camera is uEye.Camera)
{
camera.EventFrame += new EventHandler(NewFrameArrived);
}
else if (camera is DirectShowCamera)
{
//other init
}
isRunning = true;
}
public void Stop()
{
if (camera is uEye.Camera)
{
camera.EventFrame -= new EventHandler(NewFrameArrived);
camera.exit;
}
else if (camera is DirectShowCamera)
{
//other stop
}
isRunning = false;
}
public void ChangeCamera(object new camera)
{
if (isRunning)
Stop()
camera = new camera();
}
void NewFrameArrived(object sender, EventArgs e)
{
uEye.Camera Camera = sender as uEye.Camera;
Int32 s32MemID;
Camera.Memory.GetActive(out s32MemID);
lock (_frameCameralocker)
{
if (_frameCamera != null)
_frameCamera.Dispose();
_frameCamera = null;
Camera.Memory.ToBitmap(s32MemID, out _frameCamera);
}
Dispatcher.Invoke(new Action(() =>
{
lock (_frameCameralocker)
{
var bitmapData = _frameCamera.LockBits(
new System.Drawing.Rectangle(0, 0, _frameCamera.Width, _frameCamera.Height),
System.Drawing.Imaging.ImageLockMode.ReadOnly, _frameCamera.PixelFormat);
if (_frameCamera.PixelFormat == System.Drawing.Imaging.PixelFormat.Format8bppIndexed)
{
DeviceSource = System.Windows.Media.Imaging.BitmapSource.Create(
bitmapData.Width, bitmapData.Height, 96, 96, System.Windows.Media.PixelFormats.Gray8, null,
bitmapData.Scan0, bitmapData.Stride * bitmapData.Height, bitmapData.Stride);
}
_frameCamera.UnlockBits(bitmapData);
if (OnNewBitmapReady != null)
OnNewBitmapReady(this, null);
}
}));
}
}
有时,当我将摄像头从uEye更改为directshow时,我在DeviceSource=System.Windows.Media.Imaging.BitmapSource.Create
(方法NewFrameArrived
)中遇到了AccessViolationException,因为我试图从退出的摄像头创建BitmapSource
myClass.Field = 42;
做
也许这对你有用
这样做的目的是使用锁来确保您不会在(几乎)同一时间两次使用同一资源:
public class MyClassWithEvent
{
public event EventHandler MyEvent;
public int Field;
}
public class MyMainClass
{
private MyClassWithEvent myClass;
private object mylock;
public void Start()
{
myClass.MyEvent += new EventHandler(doSomething);
}
public void Stop()
{
myClass.MyEvent -= new EventHandler(doSomething);
Monitor.Enter(mylock); //If somebody else already took the lock, we will wait here
myClass = null;
Monitor.Exit(mylock); //We release the lock, so others can access it
}
private void doSomething()
{
Monitor.Enter(mylock);
if myClass != null
{
myClass.Field = 42;
}
Monitor.Exit(mylock);
}
}
编辑
根据评论,使用()会更好:
根据您更新的问题,您只需将
Stop()
操作锁定在与Dispatcher.Invoke相同的锁中即可
public void Stop()
{
lock(_frameCameralocker)
{
if (camera is uEye.Camera)
{
camera.EventFrame -= new EventHandler(NewFrameArrived);
camera.exit;
}
else if (camera is DirectShowCamera)
{
//other stop
}
isRunning = false;
}
}
这将确保所有NewFrameArrived
调用在创建新相机之前已完成或尚未启动。然后在dispatcher内部检查您是否正在运行,以防在Stop()
调用启动和完成之前帧排队
Dispatcher.Invoke(new Action(() =>
{
lock (_frameCameralocker)
{
if(!isRunning)
return;
var bitmapData = _frameCamera.LockBits(
new System.Drawing.Rectangle(0, 0, _frameCamera.Width, _frameCamera.Height),
System.Drawing.Imaging.ImageLockMode.ReadOnly, _frameCamera.PixelFormat);
if (_frameCamera.PixelFormat == System.Drawing.Imaging.PixelFormat.Format8bppIndexed)
{
DeviceSource = System.Windows.Media.Imaging.BitmapSource.Create(
bitmapData.Width, bitmapData.Height, 96, 96, System.Windows.Media.PixelFormats.Gray8, null,
bitmapData.Scan0, bitmapData.Stride * bitmapData.Height, bitmapData.Stride);
}
_frameCamera.UnlockBits(bitmapData);
if (OnNewBitmapReady != null)
OnNewBitmapReady(this, null);
}
}));
在赋值之前检查它是否为null?我的示例可能太简单了,我可以使用其他case而不使用myClass
。我将编辑我的问题以显示其他大小写。@仅检查一次不会解决问题,因为我的类可以在检查后和使用前分配为null。这就是为什么我建议在本地值中保留对myClass的引用。您还没有显示引发事件的代码或发生这种情况的位置/原因。除非这是程序的异步或并行部分,否则不应在语句之间引发事件。这意味着在第一段代码中引发事件应该发生在停止之前
,或者之后它不会调用doSomething
。在上一个示例中,在将字段
设置为101.@A.pissict之后,在执行某个稍后的代码之前不应引发该事件。在发生Stop()
锁定之前,您仍然可能遇到调度程序排队的问题。您只需在dispatcher中输入一个IsRunning
复选框,查看我的答案。我用另一个案例编辑了我的问题,您的解决方案将不适用于第二个案例。我正在寻找一种同步机制在这种情况下,请看一下ReaderWriterLockSlim,我认为它对您很有用,因为您正在尝试控制写操作。MSDN link无需使用监视器
只需使用锁定
。使用锁定或尝试最终锁定对象。我使用了自己的锁定(请参见edit2)而不是监视器
,我现在没有异常
public void Stop()
{
lock(_frameCameralocker)
{
if (camera is uEye.Camera)
{
camera.EventFrame -= new EventHandler(NewFrameArrived);
camera.exit;
}
else if (camera is DirectShowCamera)
{
//other stop
}
isRunning = false;
}
}
Dispatcher.Invoke(new Action(() =>
{
lock (_frameCameralocker)
{
if(!isRunning)
return;
var bitmapData = _frameCamera.LockBits(
new System.Drawing.Rectangle(0, 0, _frameCamera.Width, _frameCamera.Height),
System.Drawing.Imaging.ImageLockMode.ReadOnly, _frameCamera.PixelFormat);
if (_frameCamera.PixelFormat == System.Drawing.Imaging.PixelFormat.Format8bppIndexed)
{
DeviceSource = System.Windows.Media.Imaging.BitmapSource.Create(
bitmapData.Width, bitmapData.Height, 96, 96, System.Windows.Media.PixelFormats.Gray8, null,
bitmapData.Scan0, bitmapData.Stride * bitmapData.Height, bitmapData.Stride);
}
_frameCamera.UnlockBits(bitmapData);
if (OnNewBitmapReady != null)
OnNewBitmapReady(this, null);
}
}));