Question

我似乎无法弄清楚我应该/不应该对我的约束做什么。我有一个WPF窗口，它使用嵌套对象的双向绑定。主要对象是Client，客户端对象具有住宅和邮件地址，其类型为Address对象。我可以毫无问题地保存客户端对象，但是当它试图保存地址对象时，它们是null或者我必须通过＆＃34; newing＆＃34;来创建它们。他们在保存之前。我假设使用数据绑定，嵌套对象将被填充，而不必做任何事情＆＃34;特殊＆＃34;也就是说不需要新建它们只是允许绑定做的工作？我做错了什么，或者我希望它对我做的太多了？

总之，对象看起来像这样

public class Client : People
{
    public int ClientID { get; set; }
    public int? ResidentialAddressID { get; set; }
    [ForeignKey("ResidentialAddressID")]
    public virtual Address ResidentialAddress { get; set; }
    public int? MailingAddressID { get; set; }
    [ForeignKey("MailingAddressID")]
    public virtual Address MailingAddress { get; set; }

}
[Table("bhs.Addresses")]
public class Address
{
    public int AddressID { get; set; }
    public string Line1 { get; set; }
    public string Line2 { get; set; }
    public string City { get; set; }
    public int? StateID { get; set; }
    public State State { get; set; }
    public string ZipCode { get; set; }
}

表格看起来像这样

People ->
PeopleID
FirstName
MiddleName
LastName
DateOfBirth
SocialSecurityNumber
Gender

Client -> 
ClientID
PeopleID
ResidentialAddressID
MailingAddressID


Addresses->
AddressID
Line1
Line2
City
StateID
ZipCode

绑定看起来像这样。

    <Label Content="First Name:" Grid.Column="0" Margin="0,1,0,0" Grid.Row="0" Foreground="White" HorizontalContentAlignment="Right" VerticalContentAlignment="Center"/>
    <TextBox Grid.Column="1" Text="{Binding FirstName}" x:Name="txtFirstName" Margin="5,5,5,5" Grid.Row="0" TextWrapping="Wrap" />
    <Label Content="Middle Name:" Grid.Column="0" Margin="0,1,0,0" Grid.Row="1" Foreground="White" HorizontalContentAlignment="Right" VerticalContentAlignment="Center"/>
    <TextBox Grid.Column="1" x:Name="txtMiddleName" Margin="5,5,5,5" Grid.Row="1" TextWrapping="Wrap" Text="{Binding MiddleName}" />
    <Label Content="Last Name:" Grid.Column="0" Grid.Row="2" Foreground="White" HorizontalContentAlignment="Right" VerticalContentAlignment="Center"/>
    <TextBox Grid.Column="1" x:Name="txtLastName" Margin="5,5,5,5" Grid.Row="2" TextWrapping="Wrap" Text="{Binding LastName}" />
    <Label Content="Date Of Birth:" Grid.Column="0" Grid.Row="3" Foreground="White" HorizontalContentAlignment="Right" VerticalContentAlignment="Center"/>
    <DatePicker Grid.Column="1" x:Name="datDateOfBirth" Margin="5,5,5,5" Grid.Row="3" SelectedDate="{Binding DateOfBirth}"/>
    <Label Content="Social Security Number:" Grid.Column="0" Grid.Row="4" Foreground="White" HorizontalContentAlignment="Right" VerticalContentAlignment="Center"/>
    <xctk:MaskedTextBox x:Name="txtSocialSecurityNumber" Text="{Binding SocialSecurityNumber}" Margin="5,5,5,5"  Grid.Column="1" Grid.Row="4" TextWrapping="Wrap" ClipboardMaskFormat="ExcludePromptAndLiterals" IncludeLiteralsInValue="False" Mask="000-00-0000"/>
    <Label Content="Gender:" Grid.Column="0" Grid.Row="5" Foreground="White" HorizontalContentAlignment="Right" VerticalContentAlignment="Center"/>
    <ComboBox Grid.Column="1" x:Name="cboGender" Grid.Row="5" Margin="5,5,5,5" SelectedValue="{Binding Gender}" />
    <Label Content="Residential Address:" Grid.Column="2" Margin="0,1,0,0" Grid.Row="2" Foreground="White" HorizontalContentAlignment="Right" VerticalContentAlignment="Center"/>
    <TextBox Grid.Column="3" Text="{Binding ResidentialAddress.Line1}" Margin="5,5,5,5" Grid.Row="0" TextWrapping="Wrap"/>           
    <TextBox Grid.Column="3" Text="{Binding ResidentialAddress.Line2}" Margin="5,5,5,5" Grid.Row="1" TextWrapping="Wrap" />
    <TextBox Grid.Column="3" Text="{Binding ResidentialAddress.City}" Margin="5,5,5,5" Grid.Row="2" TextWrapping="Wrap" />
    <ComboBox Grid.Column="3" SelectedValue="{Binding ResidentialAddress.State}" Margin="5,5,5,5" Grid.Row="3"/>
    <TextBox Grid.Column="3" Text="{Binding ResidentialAddress.Zip}" Margin="5,5,5,5" Grid.Row="4" TextWrapping="Wrap" />

非常感谢任何帮助。

Answer 1

您必须初始化对象。

{Binding FirstName}

可以使用，因为您要将此属性设置为某个内容。

{Binding ResidentialAddress.City}

不是因为ResidentialAddress不存在，因此您无法访问其中的字段。 WPF无法知道它需要初始化您的对象以及要使用的构造函数。

你可以做的就是获得你想要的东西：

private Address _MailingAddress;
[ForeignKey("MailingAddressID")]
public virtual Address MailingAddress 
{
    get
    {
        return _MailingAddress ?? (_MailingAddress = new Address());
    }
    set
    {
        _MailingAddress = value;
    }
}

这样，您的对象在第一次访问时就会被初始化，如果它是null。否则你可以“新起来”＃34;正如你在构造函数中所说的那样。

空引用异常实体framewwork绑定到WPF窗口

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