Back and forth string format not converting and issues with CanExecute.

Question

I've made a WPF app which takes data from a SQLite table and displays them in a datagrid after filtering using the combo box selected item and a further filter textbox if required. I've also added a CRUD form which appears after a row from the datagrid is selected and the respected column values are displayed in some textbox's and datepicker's.

I'm currently having a couple of issues with this app.

Issue 1:
I want the datepicker's to show the date in the format dd-MM-yyyy but when I save the data it should be saved in the database table in the yyyy-MM-dd format, but that is not happening.

Issue 2:
If I add the parameter CanDoSave in the Save button command i.e. SaveCommand = new RelayCommand(DoSave, CanDoSave); where

        bool CanDoSave(object param)  
        {  
  
            var bill = SelectedInv as Bills;  
            float f = 0;  
  
            if (string.IsNullOrEmpty(bill.Party) || string.IsNullOrEmpty(bill.BillNo)|| string.IsNullOrEmpty(bill.BillDt) || string.IsNullOrEmpty(bill.DueDt)||!float.TryParse(bill.Amt, out f))  
            {  
                return false;  
            }  
  
  
            else  
                return true;  
        }  

I get an error

How do I solve these.

I've shared by project here for checking/testing

Answer 1

For issue 1:

I bound PaidOn with TextBox in the Remark column for testing, and the code is as follows. You could see if it suits your needs.

<DatePicker  
 FontSize="14"   
 SelectedDate="{Binding PaidOn , Converter={StaticResource converter}, BindingGroupName=Group1, UpdateSourceTrigger=PropertyChanged}"  
 Grid.Column="1"  
 Grid.Row="6" />  
                    <TextBox  
 FontSize="14"  
 Text="{Binding PaidOn, BindingGroupName=Group1, UpdateSourceTrigger=PropertyChanged}"  
 Grid.Column="1"  
 Grid.Row="7"  
 Foreground="#80D8FF"  
 Background="Transparent" />  

245104-datetimeconverters.txt
The result:
After selecting date through Datapicker: The data of the Remark row comes from the data of PaidOn in the data table(replace the original line 7 for testing).

For issue 2:

You could use Binding Validation to verify whether the input of Item's information is correct. Then trigger the Button Enable based on the validation information.
For more information, you can refer to How to: Implement Binding Validation.
Code tested with Amt and BillNo .

Xaml code:

245423-enable-button-by-validation.txt

SaveCommand = new RelayCommand(DoSave);  


public class TextBoxNotEmptyValidationRule : ValidationRule  
{  
    public override ValidationResult Validate(object value, System.Globalization.CultureInfo cultureInfo)  
    {  
        string str = value as string;  
        bool f = !string.IsNullOrEmpty(str);  
  
  
        return new ValidationResult(f, Message);  
    }  
    public String Message { get; set; }  
}  
     
public class NumericValidationRule : ValidationRule  
{  
  
    public override ValidationResult Validate(object value, System.Globalization.CultureInfo cultureInfo)  
    {  
        decimal result = 1.0M;  
        bool canConvert = decimal.TryParse(value as string, out result);  
        return new ValidationResult(canConvert, Message);  
    }  
    public String Message { get; set; }  
}  

Button disable:

Button enable:

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