Caliburn.Micro MVVM WPF - 在用户编辑 DataGrid 时启用按钮，否则禁用它

Question

I am new to MVVM and Caliburn.Micro.

I have implemented a DataGrid that is binded to <BindableCollection><CustomerModel> where CustomerModel is:

    public class CustomerModel
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string StreetName { get; set; }
    public int HouseNumber { get; set; }
    public string ApartmentNumber { get; set; }
    public string PostalCode { get; set; }
    public string Town { get; set; }
    public int PhoneNumber { get; set; }
    public string DateOfBirth { get; set; }
    public int Age { get; set; }
}

This data is loaded from XML file on startup and also can be saved into an XML file by clicking on a button "Save" which is connected to method SaveToXML() and obviously to CanSaveToXML(). Saving and loading works perfectly but I want to make the "Save" button enabled only if the user has edited the DataGrid, otherwise it should stay disabled.

I have tried comparing the current number of objects of CustomerModel class to the number of objects of CustomerModel at startup. If the number is different, it should enable the button as it indicates that someone has entered or deleted an entry.

        public bool CanSaveToXML()
    {
        if (CustomersOnStartup != Customers.Count())
            return true;
        else
            return false;
    }

where

public BindableCollection<CustomerModel> Customers { get; set; }

The problem is that the Customers.Count() is executed only once and the number doesn't update after the startup and adding/deleting an entry by the user. I know that it is probably connected to

NotifyOfPropertyChange(() => ???)

but I have no idea how to use it in relation to number of objects with Customers.Count()

Any ideas are welcome.

XAML implemenetation:

    <Grid>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="20"/>
        <ColumnDefinition Width="*"/>
        <ColumnDefinition Width="20"/>

    </Grid.ColumnDefinitions>
    <Grid.RowDefinitions>
        <RowDefinition Height="20"/>
        <RowDefinition Height="auto"/>
        <RowDefinition Height="*"/>
        <RowDefinition Height="20"/>
        <RowDefinition Height="20"/>
    </Grid.RowDefinitions>
    <DataGrid Grid.Row="1" Grid.Column="1" x:Name="Customers" AlternatingRowBackground="LightGray"
              AutoGenerateColumns="False">
        <DataGrid.Columns>
            <DataGridTextColumn Header="First Name" Width="auto" Binding="{Binding Path=FirstName, Mode=TwoWay}" />
            <DataGridTextColumn Header="Last Name" Width="auto" Binding="{Binding Path=LastName}" />
            <DataGridTextColumn Header="Street Name" Width="auto" Binding="{Binding Path=StreetName}" />
            <DataGridTextColumn Header="House Number" Width="auto" Binding="{Binding Path=HouseNumber}" />
            <DataGridTextColumn Header="Apartment Number" Width="auto" Binding="{Binding Path=ApartmentNumber}" />
            <DataGridTextColumn Header="Postal Code" Width="auto" Binding="{Binding Path=PostalCode}" />
            <DataGridTextColumn Header="Town" Width="auto" Binding="{Binding Path=Town}" />
            <DataGridTextColumn Header="Phone Number" Width="auto" Binding="{Binding Path=PhoneNumber}" />
            <DataGridTextColumn Header="Date of Birth" Width="auto" Binding="{Binding Path=DateOfBirth}" />
            <DataGridTextColumn Header="Age" Width="auto" Binding="{Binding Path=Age}" IsReadOnly="True"/>
        </DataGrid.Columns>
    </DataGrid>
    <Button x:Name="SaveToXML" Content="Save" Grid.Column="1" Grid.Row="3" Width="50" HorizontalAlignment="Left"/>
</Grid>

Answer 1

If you want to test the count number of the collection, you have to use a property which follows it:

    private int initcount;
    public YourViewModel()//constructor
    {
        RecordNbr = People.Count;
        initcount = RecordNbr;
    }

    //Property whixh follows the number of count
    private int _recordNbr;
    public int RecordNbr
    {
        get => _recordNbr;
        set
        {
            _recordNbr = value;
            NotifyOfPropertyChange(() => RecordNbr);
            NotifyOfPropertyChange(() => CanSaveToXML);
        }
    }

    public void SaveToXML()
    {

    }

    public bool CanSaveToXML
    {
        get => initcount == RecordNbr;
    }

    public void RemoveItem()
    {
       if (People.Count == 0) return;

        People.RemoveAt(0);
        RecordNbr = People.Count;
    }