Build Your Own ASP.NET 3.5 Website Using C# & VB (104 page)

Visual Basic

LearningASP\VB\ReadFile_1.aspx
(excerpt)

<%@ Page Language="VB" %>

<%@ Import Namespace="System.IO" %>

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Working with Files and Email

605

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

As you can see, we’ve simply added a Button and Label to the page. When the user

clicks the button, the Click event will be raised and the ReadText method will be

called. Let’s add this method next. It will read the text from the text file and write

it out to the Label control:

Visual Basic

LearningASP\VB\ReadFile_2.aspx
(excerpt)

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Build Your Own ASP.NET 3.5 Web Site Using C# & VB

C#

LearningASP\CS\ReadFile_2.aspx
(excerpt)

We declare a new string variable named inputString to hold the text we’ll read

from the text file. Next, we set the text value of the Label control to an empty string.

We do this in case the user presses the
Read
button when the Label already contains

text from a previous click.

The next thing our method has to do is call the OpenText method of the File class

to return a new StreamReader, again passing in the full path to the text file. And,

once again, we’re using the Using construct to ensure the stream object is disposed

of after we finish working with it:

Visual Basic

LearningASP\VB\ReadFile_2.aspx
(excerpt)

Using streamReader As StreamReader = _

File.OpenText(MapPath("myText.txt"))

C#

LearningASP\CS\ReadFile_2.aspx
(excerpt)

using (StreamReader streamReader =

File.OpenText(MapPath("myText.txt")))

{

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Next, we call the ReadLine method of the streamReader object to get the first line

of the file:

Visual Basic

LearningASP\VB\ReadFile_2.aspx
(excerpt)

inputString = streamReader.ReadLine()

C#

LearningASP\CS\ReadFile_2.aspx
(excerpt)

inputString = streamReader.ReadLine();

Now we loop through the file, reading each line and adding it, in turn, to the end

of the text in the Label:

Visual Basic

LearningASP\VB\ReadFile_2.aspx
(excerpt)

While (inputString <> Nothing)

resultLabel.Text &= inputString & "
"

inputString = streamReader.ReadLine()

End While

C#

LearningASP\CS\ReadFile_2.aspx
(excerpt)

while (inputString != null)

{

resultLabel.Text += inputString + "
";

inputString = streamReader.ReadLine();

}

Remember, While loops are used when you want to repeat the loop while a condition

remains True. In this case, we want to loop through the file, reading in lines from

it until the ReadLine method returns the value Nothing (null in C#), which indicates

that we’ve reached the end of the file. Within the loop, we simply append the value

of inputString to the Label control’s Text property using the &= operator (+= in

C#), then read the next line from streamReader into inputString.

Save your work and test the results in the browser
. Figure 14.7 shows the contents

of the text file, as displayed by
ReadFile.aspx
.

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Build Your Own ASP.NET 3.5 Web Site Using C# & VB

Figure 14.7. Reading a file using StreamReader

Accessing Directories and

Directory Information

Now that you have some understanding of writing to and reading from text files,

let’s look at accessing the directories in which those files are located. The classes

that are available in the System.IO namespace for working with directories and

directory information are as follows:

Directory

contains shared/static methods for creating, moving, and retrieving the contents

of directories

DirectoryInfo

contains instance methods for creating, moving, and retrieving the contents of

directories

Just like the File class, the Directory class contains shared/static methods, which

we can call without instantiating the class. The DirectoryInfo class, on the other

hand, requires instantiation, as it contains only instance methods. The Directory

class contains the following useful methods:

GetDirectories

returns a string array of directory names

GetFiles

returns a string array of filenames from a specific drive or directory

GetFileSystemEntries

returns a string array of directory and filenames

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Let’s build an example page with a DropDownList control to display the directories

and files within the server’s
C:
drive. In the same
Learning
folder, create a web form named
Directories.aspx
, without a code-behind file, then add to it the code shown

here in bold:

Visual Basic

LearningASP\VB\Directories_1.aspx
(excerpt)

<%@ Page Language="VB" %>

<%@ Import Namespace="System.IO" %>

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

As you can see, our interface consists of a DropDownList control containing the

three choices from which the user can select (
Directories
,
Files
, or
Directories/Files
). When a user selects an item from the DropDownList control, the SelectedIndexChanged event is raised, and ViewDriveInfo is called. Licensed to [email protected]

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Build Your Own ASP.NET 3.5 Web Site Using C# & VB

Now, let’s write the ViewDriveInfo method, which will write the specified information to the GridView control:
Visual Basic

LearningASP\VB\Directories_2.aspx
(excerpt)

C#

LearningASP\CS\Directories_2.aspx
(excerpt)

You might remember from
Chapter 3
that we use Select Case (VB) or switch (C#) statements to check for the possibility of multiple values of an object, rather than

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611

just one. The Select Case or switch specifies the value that is to be checked (in

this case, the Text property of the selected list item):

Visual Basic

LearningASP\VB\Directories_2.aspx
(excerpt)

Select Case dirDropDown.SelectedItem.Text

C#

LearningASP\CS\Directories_2.aspx
(excerpt)

switch (dirDropDown.SelectedItem.Text)

Next, we use Case to specify the action to be performed for each significant value.

The data retrieved by the GetDirectories, GetFiles, or GetFileSystemEntries

method of Directory can be fed to the GridView as its DataSource. After we specify

the DataSource, we need to call the control’s DataBind method, as if we were

reading from a database, to fetch and display the data from the data source.

Save your work and test the results in your browser.
Figure 14.8
shows within the GridView the kind of results that display when the user selects an item from the

DropDownList.

Figure 14.8. Using the Directory class to view specific files, directories, or both, from a given drive Licensed to [email protected]