WPF 與 ElementName 綁定不會更新值

Question

我將一個 Label 綁定到用戶帳戶的 ComboBox 的 SelectedItem。 根據您選擇的內容，標簽會顯示該帳戶的相應余額。 它完美地顯示了不同帳戶的余額，但是當我檢查用戶輸入的金額沒有超過他所選帳戶的余額時，余額永遠不會改變。 假設 Account1 的余額為 1500，Account2 的余額為 4000。選擇 Account1 在標簽中顯示 1500，選擇 Account2 在標簽中顯示 4000。

但是無論我選擇哪個帳戶，我的 ViewModel 中的 Balance 屬性都保持 4000。

我使用 Caliburn.Micro 來幫助處理 MVVM 部分。

我的標簽：

<Label x:Name="Balance"
                   Content="{Binding ElementName=Sender, Path=SelectedItem.Balance, Mode=OneWay, UpdateSourceTrigger=PropertyChanged}"
                   DockPanel.Dock="Right"
                   HorizontalContentAlignment="Right"
                   Language="da-DK"
                   ContentStringFormat="{}{0:C}"
                   Style="{StaticResource InputBoxPayments}"/>

我的組合框

<xctk:WatermarkComboBox x:Name="Sender"
                                    ItemsSource="{Binding Sender, UpdateSourceTrigger=PropertyChanged}"
                                    SelectedItem="{Binding SelectedAccountNmb, Mode=OneTime, UpdateSourceTrigger=PropertyChanged}"
                                    SelectedValue="{Binding Path=SelectedAccountNmb, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
                                    SelectedValuePath="AccountNmb"
                                    DisplayMemberPath="AccountName"
                                    DockPanel.Dock="Right"
                                    Watermark="Vælg din konto..."
                                    Style="{StaticResource InputBoxPayments}"/>

我的視圖模型

        private string _accountNmb;
        private string _accountType;
        private string _accountName;
        private decimal _balance;
        private BindingList<AccountModel> _sender = new BindingList<AccountModel>();
        private string _selectedAccountNmb;
        private decimal _amount;
        private string _note;
        private string _receiver;

        public string AccountNmb
        {
            get { return _accountNmb; }
            set
            {
                _accountNmb = value;
                NotifyOfPropertyChange(() => AccountNmb);
            }
        }
        public string AccountType
        {
            get { return _accountType; }
            set
            {
                _accountType = value;
                NotifyOfPropertyChange(() => AccountType);
            }
        }
        public string AccountName
        {
            get { return _accountName; }
            set
            {
                _accountName = value;
                NotifyOfPropertyChange(() => AccountName);
            }
        }
        public decimal Balance
        {
            get { return _balance; }
            set
            {
                _balance = value;
                NotifyOfPropertyChange(() => Balance);
                NotifyOfPropertyChange(() => CanMakePayment);
            }
        }
        public BindingList<AccountModel> Sender
        {
            get { return _sender; }
            set
            {
                _sender = value;
                NotifyOfPropertyChange(() => Sender);
                NotifyOfPropertyChange(() => CanMakePayment);
            }
        }
        public string SelectedAccountNmb
        {
            get { return _selectedAccountNmb; }
            set
            {
                _selectedAccountNmb = value;
                NotifyOfPropertyChange(() => SelectedAccountNmb);
                NotifyOfPropertyChange(() => CanMakePayment);
            }
        }
        public decimal Amount
        {
            get { return _amount; }
            set
            {
                _amount = value;
                NotifyOfPropertyChange(() => Amount);
                NotifyOfPropertyChange(() => CanMakePayment);
            }
        }
        public string Note
        {
            get { return _note; }
            set
            {
                _note = value;
                NotifyOfPropertyChange(() => Note);
                NotifyOfPropertyChange(() => CanMakePayment);
            }
        }
        public string Receiver
        {
            get { return _receiver; }
            set
            {
                _receiver = value;
                NotifyOfPropertyChange(() => Receiver);
                NotifyOfPropertyChange(() => CanMakePayment);
            }
        }

        public bool CanMakePayment
        {
            get
            {
                bool output = false;

                if (SelectedAccountNmb?.Length > 0 &&
                    Note?.Length > 0 &&
                    Receiver?.Length > 0 &&
                    SelectedAccountNmb != Receiver &&
                    Amount > 0 &&
                    Amount <= Balance) // This is where i make sure the amount the user types in doesn't exceed his balance.
                {
                    output = true;
                }

                return output;
            }
        }

// Omitted rest of the file

Answer 1

在您的 Combobox 中， SelectedItem是SelectedAccountNmb ，它是一個字符串屬性； 並且在您的 Label 內容中，您將綁定到您的 Combobox SelectedItem ，它是string並且沒有Balance 。

你可以這樣做：

  public AccountNmb SelectedAccountNmb
    {
        get { return _selectedAccountNmb; }
        set
        {
            _selectedAccountNmb = value;
            NotifyOfPropertyChange(() => SelectedAccountNmb);
            NotifyOfPropertyChange(() => CanMakePayment);
        }
    }

而且您不需要在 Combobox 中綁定SelectedValue ，因為您可以從SelectedAccountNmb屬性中獲取值