320 Part II Programming Fundamentals
Examine the Text Browser program code- On the File menu of the Text Browser form, double-click the Open command.
The OpenToolStripMenuItem_Click event procedure appears in the Code Editor.- Resize the Code Editor to see more of the program code, if necessary.
The OpenToolStripMenuItem_Click event procedure contains the following
program code:
Dim AllText As String = ""
OpenFileDialog1.Filter = "Text files (*.txt)|*.txt"
If OpenFileDialog1.ShowDialog() = DialogResult.OK Then 'display Open dialog box
Try 'open file and trap any errors using handler
AllText = My.Computer.FileSystem.ReadAllText(OpenFileDialog1.FileName)
lblNote.Text = OpenFileDialog1.FileName 'update label
txtNote.Text = AllText 'display file
txtNote.Enabled = True 'allow text cursor
CloseToolStripMenuItem.Enabled = True 'enable Close command
OpenToolStripMenuItem.Enabled = False 'disable Open command
Catch ex As Exception
MsgBox("An error occurred." & vbCrLf & ex.Message)
End Try
End If
This event procedure performs the following actions:
o Declares variables and assigns a value to the Filter property of the open file
dialog object.
o Prompts the user for a path by using the OpenFileDialog1 object.
o Traps errors by using a Try... Catch code block.
o Reads the entire contents of the specified file by using the ReadAllText method.
o Copies the contents of the file into a string named AllText. The AllText string has
room for a very large file, but if an error occurs during the copying process, the
Catch clause displays the error.
o Displays the AllText string in the text box, and enables the scroll bars and text
cursor.
o Updates the File menu commands.
Take a moment to see how the statements in the OpenToolStripMenuItem_Click
event procedure work—especially the ReadAllText method. The error handler in the
procedure displays a message and aborts the loading process if an error occurs.Tip For more information about the statements and methods, highlight the keyword
you’re interested in, and then press F1 to see a discussion of it in the Visual Studio Help
documentation.