ViewModel LifeCycle，何时处置? [英] ViewModel LifeCycle, when does it get disposed?
问题描述
在mvvmcross v3 ViewModel中
In mvvmcross v3 ViewModel
public class TimerViewModel : MvxViewModel
{
System.Timers.Timer timer;
public TimerViewModel()
{
timer = new System.Timers.Timer(500f);
timer.Elapsed += HandleTimerElapsed;
timer.Start();
}
void HandleTimerElapsed (object sender, ElapsedEventArgs e)
{
Debug.Log( "Time Elapsed" );
}
}
由于MvxViewModel没有实现IDisposable，因此应将以下代码放在哪里?
As MvxViewModel doesn't implement IDisposable, where should I put the following code ?
timer.Stop();
timer.Elapsed += HandleTimerElapsed;
我发现mvvmcross代码具有一些MvxWeakEventSubscription，它用于解决我的问题吗?
I find that mvvmcross code have some MvxWeakEventSubscription, is it used to solve my problem ?
推荐答案
尚不存在一种简单的通用方法来知道何时dispose ViewModel-特别是一旦您开始混合并匹配ViewModel表示样式以包括导航，选项卡，拆分视图，弹出窗口，片段，列表等，并且随着您包括越来越多的平台
There's no easy universal way to know when to dispose the ViewModel - especially once you start mixing and matching ViewModel presentation styles to include navigations, tabs, splitviews, flyouts, fragments, lists, etc. and as you include more and more platforms
因此，我过去有几种关闭计时器的方法是:
As a result of this, a couple of ways I have shut things like timers down in the past are:
1..有时候，我在ViewModel上使用了专门的接口，并确保在每个客户端上都可以正确调用它.
1. Sometimes I have used a specialised interface on the ViewModel and I ensure this is called appropriately on each client.
例如，我已经使用以下方法完成了页面"级视图的一些启动/停止操作:
For example, I have done some starting/stopping of 'page' level Views using:
- Android中的OnPause/OnResume 在Windows中
- OnNavigatedTo/OnNavigatingFrom
- iOS中的ViewDidAppear/ViewWillDisappear
- OnPause/OnResume in Android
- OnNavigatedTo/OnNavigatingFrom in Windows
- ViewDidAppear/ViewWillDisappear in iOS
我已经考虑过将其添加为通用模式来执行此操作(它已登录 https: //github.com/slodge/MvvmCross/issues/74 )-但到目前为止，我还没有将其添加到v3，因为我认为这会导致用户之间的误解-最好让他们这样做在极少数需要的情况下可以做到这一点.
I have thought about adding this as a generalised pattern to do this (it is logged in https://github.com/slodge/MvvmCross/issues/74) - but so far I've not added this to v3 as I think it would lead to too much misunderstanding among users - it's better to let them to do this in the very few situations where it's needed.
Update: I have blogged about this and published a sample - see http://slodge.blogspot.co.uk/2013/11/n42-is-my-viewmodel-visible-can-i-kill.html
2.有时，我刚刚通过MvvmCross Messenger使用了事件聚合-并且我使用了其基于WeakReference的固有消息传递功能，以确保在查看视图时可以对ViewModel进行垃圾收集已经完成了.
2. Sometimes I've just used Event Aggregation through the MvvmCross Messenger - and I've used it's inherent WeakReference-based messaging to make sure the ViewModel can be garbage collected when the view has finished with it.
InternetMinute示例中有一个示例-该示例具有一个滴答生成服务"，ViewModel可以通过消息传递连接该滴答生成服务以进行更新-请参阅:
An example of this is in the InternetMinute sample - which has a single 'Tick generation service' which ViewModels can connect to via messaging for updates - see:
- 服务- https://github .com/slodge/MvvmCross-Tutorials/tree/master/InternetMinute/InternetMinute.Core/Services/Tick
- 使用服务的ViewModel-通过
- the service - https://github.com/slodge/MvvmCross-Tutorials/tree/master/InternetMinute/InternetMinute.Core/Services/Tick
- a ViewModel that consumes the service - via https://github.com/slodge/MvvmCross-Tutorials/blob/master/InternetMinute/InternetMinute.Core/ViewModels/HomeViewModel.cs
您可能会认为这效率低下-因为即使ViewModel不存在也会生成Tick消息-但这只是一个很小的效率低下.
You might consider this slightly inefficient - as the Tick messages will be generated even if the ViewModel isn't present - but it's only a small inefficiency.
3.我考虑过使用更多的最终事件-诸如OnNavigatingFrom(BACK)和'onDestroy'之类的东西以及对UINavigationController委托的一些'最终'检测...但是我还没有一个为何在任何项目上都做到真正".
3. I've considered using more final events - things like OnNavigatingFrom(BACK) and 'onDestroy' and some 'final' detection on the UINavigationController delegates ... but I've not had a reason to do this 'for real' on any project yet.
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