March 2008 - Posts

03-26-2008 6:43 PM

Another simple use of extension methods!!

While my team and I doing our daily work. One of our new team members asked that he needs the user to select a value from drop-down list and this value should be converted to a nullable integer value.

The small issue he faces that he need to parse the value selected in one line of code and make sure that if the user does not select a value the default value will be parsed to null and do not cause a problem -in each drop-down there is a "[Select]" item with empty string value  -

I wondered a int.Parse function returns null when the parsed value is null  but throws  "Input string was not in a correct format" exception when try to parse an empty string. And when use int.TryParse  it will result with 0 value when parsing operation failed.

In such simple scenario extension methods proof it self. Simply we can create an extension method call it SafeParse for example ....

public static int? SafeParse(this String Value)
    {
        if (string.IsNullOrEmpty(Value))
            return null;
        else
            return int.Parse(Value);
    } 
 
and then you could simply use it like this:
 
int? MyNullableValue;
MyNullableValue = DropDownList1.SelectedValue.SafeParse();
 
Extension methods provide a simple and easy use which will ease programmer day day work, and make simple issues disappear just like 1,2,3 
 
Thanks for VS2008,thanks for extension methods, thanks for Microsoft team
 
Happy programming...!!
Posted by Huthaifa Afanah | with no comments
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03-12-2008 5:53 PM

Tips & Tricks: Details View and Read-only Fields

One of the flexible and new features came with ASP.NET 2.0 was DetailsView control. This data bound control is used to display the values of a single record from a data source in an HTML table, where each table row represents a field of the record. The DetailsView control allows you to edit, delete, and insert records. In this post I will explain an issue related with Read-only data fields.

 

  

We will bound a DetailsView control to a SqlDataSource for simplicity reason you can use any data source control ... I used PetShop sample database for this example. After configuring the petShopSqlDataSource and enable update, insert and delete we set the DetailsView DataSourceId to our petShopSqlDataSource Id and so the DetailsView now have 3 fields bound to Category table.

What we need here is simple modification. I will edit the DetailsView filed and make the Name filed a read only filed by setting the Read-only property to true. And I already made this column does not accept null values in Category table.

What will happen here is when we try to update any record in the details view our application will throw this exception:

"Cannot insert the value NULL into column 'Name', table 'Petshop.dbo.Category'; column does not allow nulls. UPDATE fails.The statement has been terminated" as the message states the Name filed value seems to be passed as null to the data source although it was appeared in the DetailsView before.

To clarify this take a look into what's happen on the ItemUpdating event, if we checked the e.NewValues.Keys collection before we set the Name filed as read-only filed we will find that this collection contains two Items: Descn,Name after we set Name as read-only filed this collection will conation the Descn filed only as the below figure shows.

The DetailsView will not pass the read-only fields to the underlying data source and this is not an issue DetailsView designed like this. Take a look to HandleUpdate method in the DetailsView control using reflector and you will find it does not include Read-only fields when extracting values from fields.

Okay, we are done here so our tip is: if you set some fields as Read-only make sure you handle this case by using appropriate update statement, setting values pragmatically ... e.g.

Hope this helps

Huthaifa

Posted by Huthaifa Afanah | with no comments
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