MVVM我可以在行为中实施逻辑代码还是应该将其全部放入VM中的绑定命令？

如何解决MVVM我可以在行为中实施逻辑代码还是应该将其全部放入VM中的绑定命令？

我有输入完成命令的行为，该命令验证输入内部的数据，以及我保存在ViewModel中的逻辑。而且，当我完成输入后，我需要将焦点更改为下一个输入（下一个输入没有x：Name，因为它位于DataTemplate内部）。要更改焦点，我需要下一个条目的对象，我可以通过他的父对象在行为文件（而不是VM）中找到该对象。是在MVVM中执行此操作的正确方法，还是我应该通过参数将条目对象传递给VM，并找到其父项，然后在VM中找到下一个条目？

行为：

using System.Windows.Input;
using Xamarin.Forms;

namespace RollPositioningMobile.ViewModels.Behaviors
{
    public class EntryCompletedBehavior : Behavior<Entry>
    {
        protected override void OnAttachedTo(Entry bindable)
        {
            base.OnAttachedTo(bindable);

            AssociatedObject = bindable;

            bindable.BindingContextChanged += Bindable_BindingContextChanged;
            bindable.Completed += Bindable_Completed;
        }
        protected override void OnDetachingFrom(Entry bindable)
        {
            base.OnDetachingFrom(bindable);

            bindable.BindingContextChanged -= Bindable_BindingContextChanged;
            bindable.Completed -= Bindable_Completed;

            AssociatedObject = null;
        }

        private void Bindable_BindingContextChanged(object sender,System.EventArgs e)
        {
            OnBindingContextChanged();
        }
        private void Bindable_Completed(object sender,System.EventArgs e)
        {
            if (Command == null) return;

            Entry entry = (Entry)sender;
            Grid circularEntriesGrid;

            //If this handler was invoked from the RequiredValueEntry,//focus on the next Entry mechanic is different
            if (entry.TabIndex == 0)
            {
                //First we need to define the main Grid,//and then find subgrid inside of the main
                Grid mainGrid = (Grid)entry.Parent.Parent;
                circularEntriesGrid = mainGrid.FindByName<Grid>("CircularEntriesGrid");
            }
            else
            {
                //Get the Frame parent and then the Grid parent of the Entry
                circularEntriesGrid = (Grid)entry.Parent.Parent;

                //Check for last entry
                if (circularEntriesGrid.Children.Count == entry.TabIndex)
                    return;
            }

            //Execution of the input data validation commands
            if (Command.CanExecute(entry.TabIndex))
                Command.Execute(entry.TabIndex);

            //Set focus on the next Entry
            if ((bool)CommandParameter)
            {
                var nextEntryFrame = (Frame)circularEntriesGrid.Children[entry.TabIndex];
                var nextEntry = (Entry)nextEntryFrame.Content;
                nextEntry.Focus();
            }
            else
            {
                entry.Focus();
            }
        }

        protected override void OnBindingContextChanged()
        {
            base.OnBindingContextChanged();
            BindingContext = AssociatedObject.BindingContext;
        }

        public Entry AssociatedObject { get; private set; }

        public static readonly BindableProperty CommandProperty =
                BindableProperty.Create("Command",typeof(ICommand),typeof(EntryCompletedBehavior),null);
        public ICommand Command
        {
            get { return (ICommand)GetValue(CommandProperty); }
            set { SetValue(CommandProperty,value); }
        }

        public static readonly BindableProperty CommandParameterProperty =
            BindableProperty.Create("CommandParameter",typeof(object),null);
        public object CommandParameter
        {
            get { return GetValue(CommandParameterProperty); }
            set { SetValue(CommandParameterProperty,value); }
        }
    }
}

VM部分：

public ICommand EntryCompletedCommand { get; protected set; }
    void EntryCompleted(object param)
    {
        var entryId = (int)param;

        //Validating required value
        if (entryId == 0)
        {
            RequiredValueIsValid = true;
            if (RequiredValue <= 0)
            {
                Application.Current.MainPage.DisplayAlert("Error",$"Required value cannot be equals to {RequiredValue}","OK");
                RequiredValueIsValid = false;
            }
            return;
        }

        //Validating actual values
        var entry = ActualValues[entryId - 1];
        var value = entry.Value;
        if (value < 0 || Math.Abs(value - RequiredValue) > Measurment.MaxOffset)
        {
            entry.Value = entry.OldValue;
            Application.Current.MainPage.DisplayAlert("Error",$"The actual and the required value should not differ more than {Measurment.MaxOffset}","OK");
            entry.IsValid = false;
            return;
        }
        entry.IsValid = true;
        RequiredValueIsValid = true;
        entry.OldValue = entry.Value;
    }

解决方法

我可以在行为中实施逻辑代码还是应该将其全部放入VM中的绑定命令？

由于您已使用MVVM，因此最好处理ViewModel中的逻辑。我们总是对元素本身进行一些自定义。

在您的情况下，必须将条目作为参数传递给ViewModel。您可以将 IsFocused 的值绑定到Model的属性，然后直接在VM中处理它。

这里有一个类似的thread，我提供了一个完整的解决方案。希望对您有帮助。