[英]Avoiding WeakEventManager and memory leaks on short lived viewmodels
I have long living models with properties displayed using a view.我有使用视图显示属性的长期存在的模型。 The DataContext on my view is a ViewModel with a short lifespan.我视图上的 DataContext 是一个生命周期很短的 ViewModel。
Examples include row viewmodels in lists.示例包括列表中的行视图模型。
To avoid memory leaks the viewmodels subscribe to models using System.Windows.WeakEventManager
.为了避免内存泄漏,视图模型使用System.Windows.WeakEventManager
订阅模型。
If I were to subscribe normally the long living model would keep the viewmodel alive.如果我要正常订阅,长寿模型将使视图模型保持活动状态。
Using the WeakEventManager in about every viewmodel seems very cumbersome.在每个视图模型中使用 WeakEventManager 似乎非常麻烦。 The usecase looks like a standard usecase for WPF.用例看起来像 WPF 的标准用例。 Am I missing a fundamental concept of WPF or C# that would help me writing better code here?我是否错过了 WPF 或 C# 的一个基本概念,可以帮助我在这里编写更好的代码?
Here is a minimal Example that Illustrates what I do right now.这是一个最小的示例,说明了我现在所做的事情。
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
//building would take place in a factory method
DataContext = new ShortLivedViewModel(new LongLivingModel());
}
}
public class ShortLivedViewModel : INotifyPropertyChanged
{
private string _myText;
public ShortLivedViewModel(LongLivingModel model)
{
model.SomeEvent += SomeEventHandler;
WeakEventManager<LongLivingModel, EventArgs>.AddHandler(model, nameof(LongLivingModel.SomeEvent),
SomeEventHandler);
}
public string MyText
{
get => _myText;
set
{
_myText = value;
PropertyChanged(this, new PropertyChangedEventArgs(nameof(MyText)));
}
}
public event PropertyChangedEventHandler PropertyChanged = delegate { };
private void SomeEventHandler(object sender, EventArgs e)
{
//The actual update content would come from the event args
MyText = Guid.NewGuid().ToString("N");
}
}
public class LongLivingModel
{
//the event does not matter too much so I omit the implementation that causes it
public EventHandler<EventArgs> SomeEvent = delegate { };
}
My question is if there is a less cumbersome way of subscribing to a long living object from a short living object.我的问题是,是否有一种不那么麻烦的方法可以从短寿命对象订阅长寿命对象。 Or if there is some facility in WPF that I am missing for this.或者,如果 WPF 中有一些我缺少的工具。
It strikes me that this would be the standard case.我觉得这将是标准情况。 What I played around with is adding an IDisposable
interface but that just leaves me with tacking when to call dispose so I can unsubscribe.我玩的是添加一个IDisposable
接口,但这只是让我确定何时调用 dispose 以便我可以取消订阅。
What I am looking for may be a combination of telling the GC that subscriptions do not count for the lifetime of the viewmodel and unsubscribing on destruction - or an even better solution.我正在寻找的可能是告诉 GC 订阅不计入视图模型的生命周期和取消订阅销毁的组合 - 或者更好的解决方案。
I think the parent viewmodel should be responsbile for getting rid of references.我认为父视图模型应该负责摆脱引用。
This is a simple example that pushes an update to each child viewmodel.这是一个向每个子视图模型推送更新的简单示例。 When a child needs to be cleaned up, it tells the parent to remove its reference.当需要清理子项时,它会告诉父项删除其引用。
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
//building would take place in a factory method
DataContext = new LongLivingModel();
LongLivingModel.AddChild();
LongLivingModel.AddChild();
}
}
public class ShortLivedViewModel : INotifyPropertyChanged
{
private readonly LongLivingModel longLivingModel;
public ShortLivedViewModel(LongLivingModel longLivingModel){
this.longLivingModel = longLivingModel;
}
private string _myText;
public string MyText
{
get => _myText;
set
{
_myText = value;
PropertyChanged(this, new PropertyChangedEventArgs(nameof(MyText)));
}
}
public void Remove(){
longLivingModel.Remove(this);
}
// INotifyPropertyChanged implementation
}
public class LongLivingModel
{
public ObservableCollection<ShortLivedViewModel> ChildViewModels { get; } = new ObservableCollection<ShortLivedViewModel>();
public void AddChild(){
ChildViewModels.Add(new ShortLivedViewModel(this));
}
public void RemoveChild(ShortLivedViewModel shortLivedViewModel) {
ChildViewModels.Remove(shortLivedViewModel);
}
public void PushToChildren(){
foreach(ShortLivedViewModel shortLivedViewModel in ChildViewModels){
shortLivedViewModel.MyText = Guid.NewGuid().ToString("N");
}
}
}
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