MvvmCross Monotouch C#-绑定Int属性-模式:TwoWay [英] MvvmCross Monotouch C# - Binding Int Property - Mode: TwoWay

问题描述

我是MvvmCross的新手，我有一个问题.

I am new to MvvmCross and I have a question.

我注意到以下绑定代码仅以一种方式起作用:

I noticed that the following binding code works in one way only:

{ this, "{'CurrentIndex':{'Path':'CurrentIndex','Mode':'TwoWay'}}" }

• CurrentIndex是视图中的Int属性
• CurrentIndex也是ViewModel中的Int属性

这种方式有效！

• ViewModel =>视图

但不是这样！

• View => ViewModel

我有一个ViewControllers集合，我的目标是在viewModel中为CurrentIndex调用DeleteCommand.

I have a collection of ViewControllers and my goal was to call a DeleteCommand for the CurrentIndex in the viewModel.

但是

"Android和Touch 2方式绑定不完整"

"Android and Touch 2 way bindings are incomplete"

参考: Mvvm的经验，事后见识，局限性吗?

我的猜测是，双向模式仅适用于控件(UILabel，UITextfield等)，不适用于属性.

My guess is the TwoWay mode only works for Controls (UILabel, UITextfield, ...) but not for Properties.

那么，有没有一种好的方法可以使它同时起作用呢?还是我的问题有其他选择吗?

So, is there a good way to make it works in both ways? Or Are there any alternatives to my problem?

帕特里克

推荐答案

为了使绑定在View和ViewModel之间传输任何值，则当值更改时，它需要挂接到某个事件中.

In order for a binding to transfer any value between a View to a ViewModel, then it needs to hook into some event when the value changes.

在ViewModel中，此事件始终是INotifyProperty接口中的事件.

In the ViewModel, this event is always the event in the INotifyProperty interface.

在视图/活动"中，使用了一个单一模式-因此每个绑定都必须挂接到一个单独的事件中.例如，使用TextChanged事件连接EditText上的Text(请参见

In the View/Activity, there is one single pattern employed - so each binding has to hook into a separate event. For example, the Text on EditText is hooked up using the TextChanged event (see MvxEditTextTextTargetBinding.cs) while the value in a SeekBar is hooked up using a Listener object rather than an event (see MvxSeekBarProgressTargetBinging.cs).

因此，如果您想为您的活动实现这种双向绑定，则可以通过以下方式实现:

So if you wanted to implement this two-way binding for your activity, then you could do this by:

• 在您的活动(MyActivity)中声明一个事件-CurrentIndexChanged-每当CurrentIndex更改时都会触发
• 为MyActivity声明自定义绑定，该绑定以编程方式链接CurrentIndex和CurrentIndexChanged
• 在安装过程中将自定义绑定添加到绑定注册表中

例如，您的活动可能包括:

For example, your activity might include:

public event EventHandler CurrentIndexChanged;

private int _currentIndex;
public int CurrentIndex
{ 
   get { return _currentIndex; } 
   set { _currentIndex = value; if (CurrentIndexChanged != null) CurrentIndexChanged(this, EventArgs.Empty); } 
}

然后您可以声明一个绑定类，如:

And you might then declare a binding class like:

public class MyBinding : MvxPropertyInfoTargetBinding<MyActivity>
{        
    public MyBinding (object target, PropertyInfo targetPropertyInfo) 
        : base(target, targetPropertyInfo)
    {
        View.CurrentIndexChanged += OnCurrentIndexChanged;
    }

    public override MvxBindingMode DefaultMode
    {
        get
        {
            return MvxBindingMode.TwoWay;
        }
    }

    private void OnCurrentIndexChanged(object sender, EventArgs ignored)
    {
        FireValueChanged(View.CurrentIndex);
    }

    protected override void Dispose(bool isDisposing)
    {
        base.Dispose(isDisposing);
        if (isDisposing)
        {
            View.CurrentIndexChanged -= OnCurrentIndexChanged;
        }
    }
}

您需要通过以下方式告知绑定系统有关此绑定的信息:

And you'd need to tell the binding system about this binding in setup like:

       registry.RegisterFactory(new MvxSimplePropertyInfoTargetBindingFactory(typeof(MyBinding), typeof(MyActivity), "CurrentIndex"));

---

但是...在实践上，如果您使用C#而不是XML进行操作，那么在这种情况下，最好使用C#来简单地更新ViewModel，而不是在这种情况下使用声明性绑定.

---

However... at a practical level, if you are operating in C# rather than in XML, then you might be better off in this case using C# to simply update the ViewModel rather than using declarative binding in this case.

要清楚...在这种情况下，我很可能只是将Activity属性写为:

To be clear... in this case, I would most probably just write the Activity property as:

public int CurrentIndex
{ 
   get { return _currentIndex; } 
   set { _currentIndex = value; ViewModel.CurrentIndex = value; } 
}

或者...我会考虑完全不在Activity中使用此属性.

Or... I'd consider not having this property in the Activity at all.

如果有帮助，请参见以下有关自定义绑定的更多信息:

If it helps, there's some more information on custom bindings in:

• MonoTouch MVVM交叉绑定到实例变量
• 在MvvmCross中如何自定义绑定属性
• MonoTouch MVVMCross binding to instance variables
• In MvvmCross how do I do custom bind properties

希望这会有所帮助！恕我直言，在使用XML时，绑定可以为您提供帮助-您不必使用它们...

Hope this helps! IMHO the bindings are there to help you when you're working in XML - you don't have to use them...

斯图尔特

更新如果要执行许多操作并遵循相同的名称模式，请使用名为 X 的属性以及已更改的名为 XChanged 然后类似的事情可能会起作用-它使用反射来自动找到事件:

UPDATE If you are going to do lots of these and follow the same name pattern - using property named X with changed EventHandler event named XChanged then something like this might work - it uses reflection to find the event automagically:

public class MyBinding<T> : MvxPropertyInfoTargetBinding<T>
    where T : class
{
    private readonly PropertyInfo _propertyInfo;
    private readonly EventInfo _eventInfo;

    public MyBinding(object target, PropertyInfo targetPropertyInfo)
        : base(target, targetPropertyInfo)
    {
        _propertyInfo = targetPropertyInfo;
        var eventName = _propertyInfo.Name + "Changed";
        _eventInfo = View.GetType().GetEvent(eventName);
        if (_eventInfo == null)
        {
            throw new MvxException("Event missing " + eventName);
        }

        if (_eventInfo.EventHandlerType != typeof(EventHandler))
        {
            throw new MvxException("Event type mismatch for " + eventName);
        }

        var addMethod = _eventInfo.GetAddMethod();
        addMethod.Invoke(View, new object[] { new EventHandler(OnChanged) });
    }

    public override MvxBindingMode DefaultMode
    {
        get
        {
            return MvxBindingMode.TwoWay;
        }
    }

    private void OnChanged(object sender, EventArgs ignored)
    {
        var value = _propertyInfo.GetValue(View, null);
        FireValueChanged(value);
    }

    protected override void Dispose(bool isDisposing)
    {
        base.Dispose(isDisposing);
        if (isDisposing)
        {
            var removeMethod = _eventInfo.GetRemoveMethod();
            removeMethod.Invoke(View, new object[] { new EventHandler(OnChanged) });
        }
    }
}

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