ObservesProperty方法不能在Prism 6中观察模型的属性

Question

我正在尝试学习Prism MVVM,我正在创建一个包含2个字段和一个按钮的窗口,当这两个字段不为空时,它会启用.

问题是我找不到让方法ObservesProperty()在一个对象上工作的方法(Pessoa在这种情况下).该CanExecuteAtualizar()方法只在app启动时调用,当我编辑文本字段Nome或Sobrenome按钮没有任何反应时,方法不会被触发...

我试图在没有模型的情况下工作Nome,直接在ViewModel中放置Sobrenome和UltimaAtualizacao属性,它工作正常,根据方法的返回禁用按钮CanExecuteAtualizar,但我想用模型代替它.有没有办法做到这一点？

ViewAViewModel.cs

public class ViewAViewModel : BindableBase
{
    private Pessoa _pessoa;

    public Pessoa Pessoa
    {
        get { return _pessoa; }
        set { SetProperty(ref _pessoa, value); }
    }

    public ICommand CommandAtualizar { get; set; }

    public ViewAViewModel()
    {
        Pessoa = new Pessoa();
        Pessoa.Nome = "Gabriel";
        CommandAtualizar = new DelegateCommand(ExecuteAtualizar, CanExecuteAtualizar).ObservesProperty(() => Pessoa.Nome).ObservesProperty(() => Pessoa.Sobrenome);
    }

    public bool CanExecuteAtualizar()
    {
        return !string.IsNullOrWhiteSpace(Pessoa.Nome) && !string.IsNullOrWhiteSpace(Pessoa.Sobrenome);
    }

    public void ExecuteAtualizar()
    {
        Pessoa.UltimaAtualizacao = DateTime.Now;
    }
}

Pessoa.cs

public class Pessoa : BindableBase
{
    private string _nome;

    public string Nome
    {
        get { return _nome; }
        set { SetProperty(ref _nome, value); }
    }

    private string _sobrenome;

    public string Sobrenome
    {
        get { return _sobrenome; }
        set { SetProperty(ref _sobrenome, value); }
    }

    private DateTime? _ultimaAtualizacao;

    public DateTime? UltimaAtualizacao
    {
        get { return _ultimaAtualizacao; }
        set { SetProperty(ref _ultimaAtualizacao, value); }
    }
}

ViewA.xaml

<UserControl x:Class="PrismDemo.Views.ViewA"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:local="clr-namespace:PrismDemo.Views"
             mc:Ignorable="d"
             d:DesignHeight="100" d:DesignWidth="500">
    <Grid Background="White">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*" />
            <ColumnDefinition Width="2*" />
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="*" />
            <RowDefinition Height="*" />
            <RowDefinition Height="*" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>

        <Label Content="Nome:"  Grid.Column="0" Grid.Row="0" HorizontalAlignment="Left" VerticalAlignment="Center" />
        <TextBox Grid.Column="1" Grid.Row="0"  Margin="3" TabIndex="0" Text="{Binding Pessoa.Nome, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />
        <Label Content="Sobrenome:"  Grid.Column="0" Grid.Row="1" HorizontalAlignment="Left" VerticalAlignment="Center" />
        <TextBox Grid.Column="1" Grid.Row="1"  Margin="3" TabIndex="1" Text="{Binding Pessoa.Sobrenome, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />
        <Label Content="Última atualização:"  Grid.Column="0" Grid.Row="2" HorizontalAlignment="Left" VerticalAlignment="Center" />
        <Label Grid.Column="1" Grid.Row="2"  Margin="3" HorizontalAlignment="Left" Content="{Binding Pessoa.UltimaAtualizacao, Mode=TwoWay}" />
        <Button Content="Atualizar" Grid.Column="1" Grid.Row="3" Width="70" Margin="2,2,3,2" HorizontalAlignment="Right" Command="{Binding CommandAtualizar}" />
    </Grid>
</UserControl>

Answer 1

DelegateCommand.ObservesPropery不支持复杂的对象属性.它仅支持定义命令中ViewModel上存在的属性.这是因为复杂对象的生命周期是未知的,如果创建了对象的许多实例,则会创建内存泄漏.我的建议是定义你这样的属性:

private Pessoa _pessoa;
public Pessoa Pessoa
{
    get { return _pessoa; }
    set 
    {
        if (_pessoa != null)
            _pessoa.PropertyChanged -= PropertyChanged; 

        SetProperty(ref _pessoa, value);


        if (_pessoa != null)
            _pessoa.PropertyChanged += PropertyChanged;
    }
}

然后在PropertyChanged方法中,调用DelegateCommand.RaiseCanExecuteChanged

编辑: Prism for Xamarin.Forms 7.0现在提供复杂的属性支持.