Jul2012
5

Enum types, FlagsAttribute & Zero value – Part 2

by nmgomes

In my previous post I wrote about why you should pay attention when using enum value Zero.

After reading that post you are probably thinking like Benjamin Roux: Why don’t you start the enum values at 0x1?

Well I could, but doing that I lose the ability to have Sync and Async mutually exclusive by design. Take a look at the following enum types:

[Flags]public enum OperationMode1{    Async = 0x1,    Sync = 0x2,    Parent = 0x4}[Flags]public enum OperationMode2{    Async = 0x0,    Sync = 0x1,    Parent = 0x2}

To achieve mutually exclusion between Sync and Async values using OperationMode1 you would have to operate both values:

protected void CheckMainOperarionMode(OperationMode1 mode){    switch (mode)    {        case (OperationMode1.Async | OperationMode1.Sync | OperationMode1.Parent):        case (OperationMode1.Async | OperationMode1.Sync):            throw new InvalidOperationException("Cannot be Sync and Async simultaneous");            break;        case (OperationMode1.Async | OperationMode1.Parent):        case (OperationMode1.Async):            break;        case (OperationMode1.Sync | OperationMode1.Parent):        case (OperationMode1.Sync):            break;        default:            throw new InvalidOperationException("No default mode specified");    }}

but this is a by design constraint in OperationMode2. Why? Simply because 0x0 is the neutral element for the bitwise OR operation.

Knowing this singularity, replacing and simplifying the previous method, you get:

protected void CheckMainOperarionMode(OperationMode2 mode){    switch (mode)    {        case (OperationMode2.Sync | OperationMode2.Parent):        case (OperationMode2.Sync):            break;        case (OperationMode2.Parent):        default:            break;    }

This means that:

  • if both Sync and Async values are specified Sync value always win (Zero is the neutral element for bitwise OR operation)
  • if no Sync value specified, the Async method is used.

Here is the final method implementation:

protected void CheckMainOperarionMode(OperationMode2 mode){    if (mode & OperationMode2.Sync == OperationMode2.Sync)    {    } else {     }}

All content above prove that Async value (0x0) is useless from the arithmetic perspective, but, without it we lose readability.

The following IF statements are logically equals but the first is definitely more readable:

if (OperationMode2.Async | OperationMode2.Parent){}if (OperationMode2.Parent){ }

Here’s another example where you can see the benefits of 0x0 value, the default value can be used explicitly.

    <my:Control runat="server" Mode="Async,Parent">    <my:Control runat="server" Mode="Parent">

Filed in: .NET | ASP.NET

Jul2012
4

Enum types, FlagsAttribute & Zero value

by nmgomes

We all know about Enums types and use them every single day. What is not that often used is to decorate the Enum type with the FlagsAttribute.

When an Enum type has the FlagsAttribute we can assign multiple values to it and thus combine multiple information into a single enum.

The enum values should be a power of two so that a bit set is achieved.

Here is a typical Enum type:

public enum OperationMode
{
    /// <summary>
    /// No operation mode
    /// </summary>
    None = 0,
    /// <summary>
    /// Standard operation mode
    /// </summary>
    Standard = 1,
    /// <summary>
    /// Accept bubble requests mode
    /// </summary>
    Parent = 2
}

In such scenario no values combination are possible. In the following scenario a default operation mode exists and combination is used:

[Flags]
public enum OperationMode
{
    /// <summary>
    /// Asynchronous operation mode
    /// </summary>
    Async = 0,
    /// <summary>
    /// Synchronous operation mode
    /// </summary>
    Sync = 1,
    /// <summary>
    /// Accept bubble requests mode
    /// </summary>
    Parent = 2
}

Now, it’s possible to do statements like:

[DefaultValue(OperationMode.Async)] [TypeConverter(typeof(EnumConverter))] public OperationMode Mode { get; set; } /// <summary> /// Gets a value indicating whether this instance supports request from childrens. /// </summary> public bool IsParent { get { return (this.Mode & OperationMode.Parent) == OperationMode.Parent; } }

or

switch (this.Mode) { case OperationMode.Sync | OperationMode.Parent: Console.WriteLine("Sync,Parent"); break;

[…]

 

But there is something that you should never forget: Zero is the absorber element for the bitwise AND operation.

So, checking for OperationMode.Async (the Zero value) mode just like the OperationMode.Parent mode makes no sense since it will always be true:

(this.Mode & 0x0) == 0x0

Instead, inverse logic should be used: OperationMode.Async = !OperationMode.Sync

public bool IsAsync
{
    get { return (this.Mode & ContentManagerOperationMode.Sync) != ContentManagerOperationMode.Sync; }
}

or

public bool IsAsync
{
    get { return (int)this.Mode == 0; }
}

[Begin: Edit]

Some readers suggested to use the Enum.HasFlag method. Although it’s another valid approach it’s also widely accepted that this method has some performance issues related an internal box/unboxing.

Use it when performance is not a problem (I see this method mostly used by rookie developers).

[End: Edit]

Final Note:

Benefits

Allow multiple values combination

The above samples snippets were taken from an ASP.NET control and enabled the following markup usage:

<my:Control runat="server" Mode="Sync,Parent">

Drawback

Zero value is the absorber element for the bitwise AND operation

Be very carefully when evaluating the Zero value, either evaluate the enum value as an integer or use inverse logic.

Filed in: ASP.NET | .NET

Jun2012
19

OpenXML error “file is corrupt and cannot be opened.”

by nmgomes

From time to time I ear some people saying their new web application supports data export to Excel format.

So far so good … but they don’t tell the all story … in fact almost all the times what is happening is they are exporting data to a Comma-Separated file or simply exporting GridView rendered HTML to an xls file.

Ok … it works but it’s not something I would be proud of.

So … yesterday I decided to take a look at the Office Open XML File Formats Specification (Microsoft Office 2007+ format) based on well-known technologies: ZIP and XML.

I start by installing Open XML SDK 2.0 for Microsoft Office and playing with some samples.

Then I decided to try it on a more complex web application and the “file is corrupt and cannot be opened.” message start happening.

Google show us that many people suffer from the same and it seems there are many reasons that can trigger this message. Some are related to the process itself, others with encodings or even styling.

Well, none solved my problem and I had to dig … well not that much, I simply change the output file extension to zip and extract the zip content.

Then I did the same to the output file from my first sample, compare both zip contents with SourceGear DiffMerge and found that my problem was Culture related.

Yes, my complex application sets the Thread.CurrentThread.CurrentCulture  to a non-English culture.

For sample purposes I was simply using the ToString method to convert numbers and dates to a string representation but forgot that XML is culture invariant and thus using a decimal separator other than “.” will result in a deserialization problem.

I solve the “file is corrupt and cannot be opened.” by using Convert.ToString(object, CultureInfo.InvariantCulture) method instead of the ToString method.

Hope this can help someone.

Filed in: .NET | ASP.NET