C# Propertygrid default value typeconverter

问题

I have a propertygrid with a dropdown box. In my application a user can click on a block and then the properties of that block are shown in a propertygrid. But the first time they click on a block an invalid value (0) is shown in the dropdown. How can I make sure that a valid value is shown?

Here is some code of the TypeConverter:

public class DynamicFormScreenId : Int32Converter
{

    public override bool GetStandardValuesSupported(ITypeDescriptorContext context)
    {
        return true;
    }

    public override StandardValuesCollection GetStandardValues(ITypeDescriptorContext context)
    {
        Database database = new Database();
        database.StoredProcedureName = "SP naam";

        int[] id = null;
        if (database.ExecuteStoredProcedure())
        {
            int totalIds = database.DataTable.Rows.Count; 
            id = new int[totalIds];

            for (int i = 0; i < totalIds; i++)
            {
                id[i] = Convert.ToInt32(database.DataTable.Rows[i][0]);
            }
        }

        return new StandardValuesCollection(id);
    }

    public override bool GetStandardValuesExclusive(
                       ITypeDescriptorContext context)
    {
        return true;
    }
}

And the property in my class:

[TypeConverter(typeof(DynamicFormScreenId)),
CategoryAttribute("Screen Settings"),
Description("The id of the screen")]
public int ScreenId
{
    get { return _screenId; }
    set { _screenId = value; }
}

SOLUTION

I set the default value of ScreenId in the constructor:

private void Constructor(string name)
{
    _controlName = name;

    // Set screenId default value
    Database database = new Database("connectionstring");
    database.StoredProcedureName = "mySP";

    if (database.ExecuteStoredProcedure())
    {
        if (database.DataTable.Rows.Count > 0)
        {
            _screenId = Convert.ToInt32(database.DataTable.Rows[0]["id"]);
        }
    }
}

回答1:

Have you tried the DefaultValueAttribute in System.ComponentModel?

From MSDN:

You can create a DefaultValueAttribute with any value. A member's default value is typically its initial value. A visual designer can use the default value to reset the member's value.

private bool myVal=false;

[DefaultValue(false)]
 public bool MyProperty {
    get {
       return myVal;
    }
    set {
       myVal=value;
    }
 }

回答2:

You will have to assign the object's ScreenId property value before you show it in the PropertyGrid. In effect, you have to run the dbase query twice. Once to know what value to assign to ScreenId, again in the type converter.

来源：https://stackoverflow.com/questions/2040620/c-sharp-propertygrid-default-value-typeconverter

标签

winforms

propertygrid