Question

如何保存ViewModel/Model传递给View的信息？我需要将此信息保存到数据库中，但为了确保检索值，我设置了MessageBox来显示是否正在检索该值。

这是我的ViewModel / Model的代码：

namespace OcelotPayroll
{
    public class PayslipModel : EmployeeModel
    {

        private decimal statIncome;
        private string totalDed;
        private string _netpay;
        private string _amount;

        public string Amount
        {
            get
            {
                return _amount;
            }
            set
            {
               _amount = value;
               OnPropertyChanged("Amount");
            }
        }


        public decimal StautoryIncome
        {
            get
            {
                return statIncome;
            }
            set
            {
                statIncome = value;
            }
        }

        public PayslipModel()
        {

            Date = DateTime.Today.Date;

            SelectAll = new DelegateCommand(Select, () => CanSelect);

            UnSelectAll = new DelegateCommand(UnSelect, () => CanUnSelect);

            SaveToDatabase = new DelegateCommand(Save, () => CanSave);

            scon = new MichaelAllenEntities();

        }

        public ICommand SaveToDatabase
        {
            get; set;
        }

        private bool CanSave
        {
            get { return Workspaces.Count > 0; }
        }

        private async void Save()
        {
            try
            {
                MessageBox.Show(StautoryIncome.ToString()); //returns 0
                MessageBox.Show(Amount.ToString()); //NullPointerException
            }
            catch (DbEntityValidationException ex)
            {
                foreach (var en in ex.EntityValidationErrors)
                {
                    var exceptionDialog = new MessageDialog
                    {
                        Message = { Text = string.Format("{0}, {1}", en.Entry.Entity.GetType().Name, en.Entry.State) }
                    };

                    await DialogHost.Show(exceptionDialog, "RootDialog");

                    foreach (var ve in en.ValidationErrors)
                    {
                        exceptionDialog = new MessageDialog
                        {
                            Message = { Text = string.Format("{0}, {1}", ve.PropertyName, ve.ErrorMessage) }
                        };

                        await DialogHost.Show(exceptionDialog, "RootDialog");
                    }
                }
            }
            catch(Exception ex)
            {
                var exceptionDialog = new MessageDialog
                {
                    Message = { Text = string.Format("{0}", ex) }
                };

                await DialogHost.Show(exceptionDialog, "RootDialog");
            }

        }

        public async void CalcNis()
        {
            try
            {
                float nis = 0;

                NisName = "N.I.S.";

                SqlConnection con = new SqlConnection(scon.Database.Connection.ConnectionString);
                con.Open();
                SqlCommand cmd = new SqlCommand("select NIS from Deductions where TaxId='1'", con);

                SqlDataReader sdr = cmd.ExecuteReader();
                while (sdr.Read())
                {
                    nis = float.Parse(sdr.GetValue(0).ToString());
                }

                con.Close();

                if (Amount != string.Empty)
                {
                     NisVal = (decimal.Parse(Amount.ToString()) * decimal.Parse(nis.ToString())).ToString("N2");
                     StautoryIncome = (decimal.Parse(Amount.ToString()) - decimal.Parse(NisVal.ToString())); //value gets assigned here
                }
            }
            catch(Exception ex)
            {
                var exceptionDialog = new MessageDialog
                {
                    Message = { Text = ex.ToString() }
                };

                await DialogHost.Show(exceptionDialog, "RootDialog");
            }
        }

    }
}

Amount的数据绑定：

<TextBlock Foreground="Black" Margin="0 0 0 0" VerticalAlignment="Top" Grid.Column="3" Text="{Binding Path=Amount, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>

您看到的所有计算都正常工作，所有值都完美地传递给View。但是，当我尝试保存时，我会收到Object Reference not set to instance of an object Exception。

如何从视图中检索值以保存到数据库？

修改：好的，我已经更新了代码，使其更容易理解。我在此行MessageBox.Show(StautoryIncome.ToString());收到错误。它保存在CalcNis()方法中计算后的值，并使用相同的值执行其他计算。但是，一旦我尝试保存，它就像StautoryIncome返回0并且任何数据绑定都返回NullPointerException。 Amount的绑定工作完美，只要我开始在Textbox中输入文字，TextBlock更新的值就相同。

Answer 1

这个问题原来是UserControls没有使用ViewModel的同一个实例。讨论转移到：Unable to retrieve binding values MVVM，它已经解决了:)。希望有人觉得它很有用。

WPF保存视图模型加载到视图中的数据

1 个答案: