Question

自两个星期以来，我一直在使用Xamarin和C＃，但是我真的在努力使像MVVM-Pattern这样的企业工作。两天以来我一直处于困境，所以我想问专家，社区。

我的问题是EntryCell没有属性“ IsPassword”，因此我创建了CostumCell，它是一个带有网格，Label和Entryinside的ViewCell。该条目具有“ IsPassword”属性，我在这里找到了

现在开始讨论实际问题。实际上，EditedEntryCell无法显示绑定文本。普通的EntryCell能够显示所有信息： SettingsPage.xaml

<TableSection>
    <EntryCell
        Label="normal entry"
        Text="{Binding Username}"/>
    <EntryCell
        Label="normal entry"
        Text="{Binding Password}"/>
    <local:EditedEntryCell
        LabelText="edited entry"
        EntryText="{Binding Password}"
        EntryIsPassword="True"/>
</TableSection>

在构建时，它会出现在输出中：

[0：]绑定：在'ProblemDemonstration.ViewModel.SettingsPageViewModel'上找不到'LabelText'属性，目标属性：'Xamarin.Forms.Label.Text'

[0：]绑定：在'ProblemDemonstration.ViewModel.SettingsPageViewModel'上找不到'EntryText'属性，目标属性：'Xamarin.Forms.Entry.Text'

[0：]绑定：在'ProblemDemonstration.ViewModel.SettingsPageViewModel'上找不到'EntryIsPassword'属性，目标属性：'Xamarin.Forms.Entry.IsPassword'

我不明白为什么绑定试图在ViewModel而不是EditedEntryCell类上找到属性，因为它们可以通过

使用

xaml xmlns:local="clr-namespace:ProblemDemonstration.Extensions"

隐藏代码如下： SettingsPage.xaml.cs

public partial class SettingsPage : ContentPage
    {
        public static readonly BindableProperty UsernameProperty =
               BindableProperty.Create(
                   propertyName: "Username",
                   returnType: typeof(string),
                   declaringType: typeof(SettingsPageViewModel));

        public static readonly BindableProperty PasswordProperty =
               BindableProperty.Create(
                   propertyName: "Password",
                   returnType: typeof(string),
                   declaringType: typeof(SettingsPageViewModel));
        public string Username
        {
            get { return (string)GetValue(UsernameProperty); }
            set { SetValue(UsernameProperty, value); }
        }
        public string Password
        {
            get { return (string)GetValue(PasswordProperty); }
            set { SetValue(PasswordProperty, value); }
        }
        public SettingsPage()
        {
            InitializeComponent();

            BindingContext = new SettingsPageViewModel(((App)Application.Current).Settings);
        }
    }

这显示CustomCell定义：

EditedEntryCell.xaml

<ViewCell ...>
    <Grid>
        ....
        <Label
            Text="{Binding LabelText}"
            Grid.Row="0"
            Grid.Column="0"
            IsVisible="{Binding BothIsVisible}"/>
        <Entry
            Text="{Binding EntryText}"
            Grid.Row="0"
            Grid.Column="1"
            IsPassword="{Binding EntryIsPassword}"
            IsEnabled="{Binding EntryIsEnabled}"
            IsVisible="{Binding BothIsVisible}"/>
    </Grid>
</ViewCell>

EditedEntryCell.xaml.cs

public partial class EditedEntryCell : ViewCell
    {
        public static readonly BindableProperty LabelTextProperty =
            BindableProperty.Create(
                propertyName: "LabelText",
                returnType: typeof(string),
                declaringType: typeof(EditedEntryCell),
                defaultValue: "default");

        public static readonly BindableProperty EntryTextProperty =
            BindableProperty.Create(
                propertyName: "EntryText",
                returnType: typeof(string),
                declaringType: typeof(EditedEntryCell),
                defaultValue: "default");

        .....

        public string LabelText
        {
            get { return (string)GetValue(LabelTextProperty); }
            set { SetValue(LabelTextProperty, value); }
        } 
        public string EntryText
        {
            get { return (string)GetValue(EntryTextProperty); }
            set { SetValue(EntryTextProperty, value); }
        }

        ....
    }

ViewModel中的代码： SettingsPageViewModel.xaml.cs

public class SettingsPageViewModel
    {
        private Settings _settings;

        public string Username
        {
            get { return _settings.Username; }
            set { _settings.Username = value; }
        }
        public string Password
        {
            get { return _settings.Password; }
            set { _settings.Password = value; }
        }

        public SettingsPageViewModel(Settings settings)
        {
            this._settings = settings;
        }
    }

Answer 1

原因：：您似乎忘记了设置BindingContext中的CustomEntryCell，因此绑定永远无法进行。

解决方案：添加以下代码

public EditedEntryCell()
{
  InitializeComponent();
  BindingContext = this;
}

如何将应用程序设置从TableView绑定到已编辑的EntryCell？

1 个答案: