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A Beginner’s Guide to Handling Text Files in Xojo

Published May 29, 2024 by Gabriel Ludosanu

As developers, we often need to work with text files. This could be for reading configuration settings, parsing log files, or generating reports. Text files are a common part of software development, and knowing how to access and manipulate them is important for building strong and flexible Xojo applications.

In this article, we will make use of the key Xojo classes and techniques for working with text files. We will start by looking at how to read the contents of text files using the TextInputStream class. You will learn how to read an entire file into a string and how to process the file line-by-line.

Next, we will cover writing to text files using the TextOutputStream class. You will see examples of how to write a complete string to a file and how to write individual lines one-by-one, useful when logging information or saving user preferences.

By the end of this post, you will understand the core techniques for accessing, reading, and writing text files in your Xojo applications. These skills will help you build more robust and flexible software that can work with a wide range of data sources and formats.

Reading Text Files

When it comes to reading the contents of text files in Xojo, the TextInputStream class is the primary tool you’ll use. This class provides methods for both reading the entire file at once, as well as reading it line-by-line.

Using TextInputStream to Open and Read Text Files

Here is an example that demonstrates how to read an entire file into a string:

// Step 1: Open the File
Var file As FolderItem
file = FolderItem.ShowOpenFileDialog("text/plain") // Show an open file dialog to select the file

If file <> Nil Then
  // Step 2: Create a TextInputStream
  Var inputStream As TextInputStream
  inputStream = TextInputStream.Open(file)
  
  // Step 3: Read the File
  Var fileContents As String
  fileContents = inputStream.ReadAll
  
  // Step 4: Close the Stream
  inputStream.Close
  
  // Output the file contents (for demonstration purposes)
  MessageBox(fileContents)
Else
  MessageBox("No file selected.")
End If

In this example:

  • The FolderItem.ShowOpenFileDialog method is used to display a file dialog, allowing the user to select a text file.
  • The TextInputStream.Open method opens the selected file for reading.
  • The ReadAll method reads the entire contents of the file into the fileContents string.
  • The Close method closes the TextInputStream.

This approach is useful when you need to process the entire contents of a text file at once. However, for larger files, you may want to read the file line-by-line to manage memory usage more efficiently, which we will cover in the next section.

Using TextInputStream to Read Line-by-Line

Reading a file line-by-line is often more efficient, especially for large files. This method allows you to process each line individually, reducing memory usage and enabling you to handle large datasets more effectively.

Here is an example that demonstrates how to read a file line-by-line in Xojo:

// Step 1: Open the File
Var file As FolderItem
file = FolderItem.ShowOpenFileDialog("text/plain") // Show an open file dialog to select the file

If file <> Nil Then
  // Step 2: Create a TextInputStream
  Var inputStream As TextInputStream
  inputStream = TextInputStream.Open(file)
  
  // Step 3: Read Each Line
  Var line As String
  While Not inputStream.EndOfFile
    line = inputStream.ReadLine
    // Process each line (for demonstration purposes, we'll just output each line in a MessageBox)
    MessageBox(line)
  Wend
  
  // Step 4: Close the Stream
  inputStream.Close
Else
  MessageBox("No file selected.")
End If

This approach is particularly useful when you need to process or analyze each line of a text file individually, such as when parsing log files or reading configuration settings.

Writing Text Files

Writing text files in Xojo is just as straightforward as reading them. The TextOutputStream class allows you to write data to text files, either all at once or line-by-line and it’s quite easy.

Using TextOutputStream to Write Entire Files

To write an entire string to a file, follow these steps:

// Step 1: Allow the user to set the path and name of the text file we are about to create
Var file As FolderItem
file = FolderItem.ShowSaveFileDialog("text/plain", "example.txt") // Show a save file dialog to specify the file

If file <> Nil Then
  // Step 2: Create a TextOutputStream
  Var outputStream As TextOutputStream
  outputStream = TextOutputStream.Create(file)
  
  // Step 3: Write to the File
  Var fileContents As String = "Hello, Xojo!"
  outputStream.Write(fileContents)
  
  // Step 4: Close the Stream
  outputStream.Close
  
  MessageBox("File written successfully.")
Else
  MessageBox("No file specified.")
End If

In this example:

  • The FolderItem.ShowSaveFileDialog method is used to display a save file dialog, allowing the user to specify the file name and location.
  • The TextOutputStream.Create method creates a new file or overwrites an existing file.
  • The Write method writes the fileContents string to the file.
  • The Close method closes the TextOutputStream.

Using TextOutputStream to Write Line-by-Line

Writing a file line-by-line is useful when you need to write data incrementally or when dealing with large datasets.

To write a file line-by-line, follow these steps:

// Step 1: Allow the user to set the path and name of the text file we are about to create
Var file As FolderItem
file = FolderItem.ShowSaveFileDialog("text/plain", "example.txt") // Show a save file dialog to specify the file

If file <> Nil Then
  // Step 2: Create a TextOutputStream
  Var outputStream As TextOutputStream
  outputStream = TextOutputStream.Create(file)
  
  // Step 3: Write Each Line
  Var lines() As String = Array("Line 1", "Line 2", "Line 3")
  For Each line As String In lines
    outputStream.WriteLine(line)
  Next
  
  // Step 4: Close the Stream
  outputStream.Close
  
  MessageBox("File written successfully.")
Else
  MessageBox("No file specified.")
End If

In this example:

  • The FolderItem.ShowSaveFileDialog method is used to display a save file dialog, allowing the user to specify the file.
  • The TextOutputStream.Create method creates a new file or overwrites an existing file.
  • The WriteLine method writes each line from the lines array to the file.
  • The Close method closes the TextOutputStream.

By understanding these methods, you can choose the one that best fits your needs. Writing the entire file at once is useful for smaller datasets or when you need to write all data simultaneously. Writing line-by-line is more efficient for larger datasets or when you need to write data incrementally.

Conclusion

This article has provided you with the skills to handle text files in Xojo using the TextInputStream and TextOutputStream classes. We covered the following essential techniques:

Reading Text Files:

  • Reading entire files into a string using TextInputStream.ReadAll
  • Reading files line-by-line using TextInputStream.ReadLine

Writing Text Files:

  • Writing entire strings to a file using TextOutputStream.Write
  • Writing lines to a file using TextOutputStream.WriteLine

Try applying these techniques in your own projects. Experiment with different methods to see how they can help you manage text files more effectively. The official Xojo documentation on working with text files is a great resource for further reading.

Ready to get started? Download Xojo for free and begin building your applications today!

Happy coding!

Gabriel is a digital marketing enthusiast who loves coding with Xojo to create cool software tools for any platform. He is always eager to learn and share new ideas!

Published in Tutorials