使用 MVVM 在 wpf 中进行对话的好坏做法? [英] Good or bad practice for Dialogs in wpf with MVVM?
问题描述
我最近在为我的 wpf 应用程序创建添加和编辑对话框时遇到了问题.
I lately had the problem of creating add and edit dialogs for my wpf app.
我想要在我的代码中做的就是这样.(我主要使用带有 mvvm 的 viewmodel 第一种方法)
All I want to do in my code was something like this. (I mostly use viewmodel first approach with mvvm)
调用对话窗口的ViewModel:
ViewModel which calls a dialog window:
var result = this.uiDialogService.ShowDialog("Dialogwindow Title", dialogwindowVM);
// Do anything with the dialog result
它是如何工作的?
首先，我创建了一个对话服务:
First, I created a dialog service:
public interface IUIWindowDialogService
{
bool? ShowDialog(string title, object datacontext);
}
public class WpfUIWindowDialogService : IUIWindowDialogService
{
public bool? ShowDialog(string title, object datacontext)
{
var win = new WindowDialog();
win.Title = title;
win.DataContext = datacontext;
return win.ShowDialog();
}
}
WindowDialog 是一个特殊但简单的窗口.我需要它来保存我的内容:
WindowDialog is a special but simple window. I need it to hold my content:
<Window x:Class="WindowDialog"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
Title="WindowDialog"
WindowStyle="SingleBorderWindow"
WindowStartupLocation="CenterOwner" SizeToContent="WidthAndHeight">
<ContentPresenter x:Name="DialogPresenter" Content="{Binding .}">
</ContentPresenter>
</Window>
wpf 中对话框的一个问题是 dialogresult = true 只能在代码中实现.这就是为什么我为我的 dialogviewmodel 创建了一个接口来实现它.
A problem with dialogs in wpf is the dialogresult = true can only be achieved in code. That's why I created an interface for my dialogviewmodel to implement it.
public class RequestCloseDialogEventArgs : EventArgs
{
public bool DialogResult { get; set; }
public RequestCloseDialogEventArgs(bool dialogresult)
{
this.DialogResult = dialogresult;
}
}
public interface IDialogResultVMHelper
{
event EventHandler<RequestCloseDialogEventArgs> RequestCloseDialog;
}
每当我的 ViewModel 认为是 dialogresult = true 的时候，就引发这个事件.
Whenever my ViewModel thinks it's time for dialogresult = true, then raise this event.
public partial class DialogWindow : Window
{
// Note: If the window is closed, it has no DialogResult
private bool _isClosed = false;
public DialogWindow()
{
InitializeComponent();
this.DialogPresenter.DataContextChanged += DialogPresenterDataContextChanged;
this.Closed += DialogWindowClosed;
}
void DialogWindowClosed(object sender, EventArgs e)
{
this._isClosed = true;
}
private void DialogPresenterDataContextChanged(object sender,
DependencyPropertyChangedEventArgs e)
{
var d = e.NewValue as IDialogResultVMHelper;
if (d == null)
return;
d.RequestCloseDialog += new EventHandler<RequestCloseDialogEventArgs>
(DialogResultTrueEvent).MakeWeak(
eh => d.RequestCloseDialog -= eh;);
}
private void DialogResultTrueEvent(object sender,
RequestCloseDialogEventArgs eventargs)
{
// Important: Do not set DialogResult for a closed window
// GC clears windows anyways and with MakeWeak it
// closes out with IDialogResultVMHelper
if(_isClosed) return;
this.DialogResult = eventargs.DialogResult;
}
}
现在至少我必须在我的资源文件中创建一个 DataTemplate(app.xaml 或其他东西):
Now at least I have to create a DataTemplate in my resource file(app.xaml or something):
<DataTemplate DataType="{x:Type DialogViewModel:EditOrNewAuswahlItemVM}" >
<DialogView:EditOrNewAuswahlItem/>
</DataTemplate>
就是这样，我现在可以从我的视图模型中调用对话框了:
Well thats all, I can now call dialogs from my viewmodels:
var result = this.uiDialogService.ShowDialog("Dialogwindow Title", dialogwindowVM);
现在我的问题是，你觉得这个解决方案有什么问题吗?
Now my question, do you see any problems with this solution?
为了完整性.ViewModel 应该实现 IDialogResultVMHelper 然后它可以在 OkCommand 或类似的东西中引发它:
for completeness. The ViewModel should implement IDialogResultVMHelper and then it can raise it within a OkCommand or something like this:
public class MyViewmodel : IDialogResultVMHelper
{
private readonly Lazy<DelegateCommand> _okCommand;
public MyViewmodel()
{
this._okCommand = new Lazy<DelegateCommand>(() =>
new DelegateCommand(() =>
InvokeRequestCloseDialog(
new RequestCloseDialogEventArgs(true)), () =>
YourConditionsGoesHere = true));
}
public ICommand OkCommand
{
get { return this._okCommand.Value; }
}
public event EventHandler<RequestCloseDialogEventArgs> RequestCloseDialog;
private void InvokeRequestCloseDialog(RequestCloseDialogEventArgs e)
{
var handler = RequestCloseDialog;
if (handler != null)
handler(this, e);
}
}
编辑 2:我使用这里的代码使我的 EventHandler 注册弱:
http://diditwith.net/2007/03/23/SolvingTheProblemWithEventsWeakEventHandlers.aspx
(网站不再存在，WebArchive镜子)
EDIT 2: I used the code from here to make my EventHandler register weak:
http://diditwith.net/2007/03/23/SolvingTheProblemWithEventsWeakEventHandlers.aspx
(Website no longer exists, WebArchive Mirror)
public delegate void UnregisterCallback<TE>(EventHandler<TE> eventHandler)
where TE : EventArgs;
public interface IWeakEventHandler<TE>
where TE : EventArgs
{
EventHandler<TE> Handler { get; }
}
public class WeakEventHandler<T, TE> : IWeakEventHandler<TE>
where T : class
where TE : EventArgs
{
private delegate void OpenEventHandler(T @this, object sender, TE e);
private readonly WeakReference mTargetRef;
private readonly OpenEventHandler mOpenHandler;
private readonly EventHandler<TE> mHandler;
private UnregisterCallback<TE> mUnregister;
public WeakEventHandler(EventHandler<TE> eventHandler,
UnregisterCallback<TE> unregister)
{
mTargetRef = new WeakReference(eventHandler.Target);
mOpenHandler = (OpenEventHandler)Delegate.CreateDelegate(
typeof(OpenEventHandler),null, eventHandler.Method);
mHandler = Invoke;
mUnregister = unregister;
}
public void Invoke(object sender, TE e)
{
T target = (T)mTargetRef.Target;
if (target != null)
mOpenHandler.Invoke(target, sender, e);
else if (mUnregister != null)
{
mUnregister(mHandler);
mUnregister = null;
}
}
public EventHandler<TE> Handler
{
get { return mHandler; }
}
public static implicit operator EventHandler<TE>(WeakEventHandler<T, TE> weh)
{
return weh.mHandler;
}
}
public static class EventHandlerUtils
{
public static EventHandler<TE> MakeWeak<TE>(this EventHandler<TE> eventHandler,
UnregisterCallback<TE> unregister)
where TE : EventArgs
{
if (eventHandler == null)
throw new ArgumentNullException("eventHandler");
if (eventHandler.Method.IsStatic || eventHandler.Target == null)
throw new ArgumentException("Only instance methods are supported.",
"eventHandler");
var wehType = typeof(WeakEventHandler<,>).MakeGenericType(
eventHandler.Method.DeclaringType, typeof(TE));
var wehConstructor = wehType.GetConstructor(new Type[]
{
typeof(EventHandler<TE>), typeof(UnregisterCallback<TE>)
});
IWeakEventHandler<TE> weh = (IWeakEventHandler<TE>)wehConstructor.Invoke(
new object[] { eventHandler, unregister });
return weh.Handler;
}
}
推荐答案
这是一个很好的方法，我过去使用过类似的方法.加油！
This is a good approach and I used similar ones in the past. Go for it!
当您需要在 DialogResult 中设置false"时，我肯定会做的一件小事是让事件接收一个布尔值.
One minor thing I'd definitely do is make the event receive a boolean for when you need to set "false" in the DialogResult.
event EventHandler<RequestCloseEventArgs> RequestCloseDialog;
和 EventArgs 类:
and the EventArgs class:
public class RequestCloseEventArgs : EventArgs
{
public RequestCloseEventArgs(bool dialogResult)
{
this.DialogResult = dialogResult;
}
public bool DialogResult { get; private set; }
}
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