sfzliujieqi / fbs-tutorial

Tutorial for creating cross-platform desktop applications with fbs

fbs tutorial

This tutorial is meant for Windows, Mac and Ubuntu. You need Python 3.5. (Later versions have known issues and are not yet supported.)

Setup

Download the Zip file of this repository and extract it. Then, open a command prompt and cd into it:

cd .../path/to/fbs-tutorial-master

Create a virtual environment:

python3 -m venv venv

Activate the virtual environment:

# On Mac/Linux:
source venv/bin/activate
# On Windows:
call venv\scripts\activate.bat

The remainder of the tutorial assumes that the virtual environment is active.

Install the required libraries (most notably, fbs and PyQt5):

pip install -r requirements.txt

Run the app

This repository contains a sample application. To run it from source, execute the following command:

python -m fbs run

This shows a (admittedly not very exciting) window. Screenshots on Windows/Mac/Ubuntu:

Freezing your app

We want to turn the source code of your app into a standalone executable that can be run on your users' computers. In the context of Python applications, this process is called "freezing".

Use the following command to turn your app's source code into a standalone executable:

python -m fbs freeze

This creates the folder target/Tutorial. You can copy this directory to any other computer (with the same OS as yours) and run your app there! Isn't that awesome?

Creating an installer

Desktop applications are normally distributed by means of an installer. On Windows, this would be an executable called TutorialSetup.exe. On Mac, mountable disk images such as Tutorial.dmg are commonly used. fbs lets you generate both of these files.

Windows installer

To create an installer on Windows, please first install NSIS and add its directory to your PATH environment variable. Then, you can run the following command:

python -m fbs installer

This creates an installer at target/TutorialSetup.exe. It lets your users pick the installation directory and adds your app to the Start Menu. It also creates an entry in Windows' list of installed programs. Your users can use this to uninstall your app. The following screenshots show these steps in action.

Mac installer

Creating an installer on Mac is done with the same command as on Windows:

python -m fbs installer

This creates the file target/Tutorial.dmg for distribution to your users. Upon opening it, the following volume is displayed:

To install your app, your users simply drag its icon to the Applications folder (also shown in the volume).

Source code of the sample app

Let's now take a look at the source code for the sample application. It is at src/main/python/main.py:

from fbs_runtime.application_context import ApplicationContext
from PyQt5.QtWidgets import QMainWindow

import sys

class AppContext(ApplicationContext):           # 1. Subclass ApplicationContext
    def run(self):                              # 2. Implement run()
        window = QMainWindow()
        window.setWindowTitle('Hello World!')
        window.resize(250, 150)
        window.show()
        return self.app.exec_()                 # 3. End run() with this line

if __name__ == '__main__':
    appctxt = AppContext()                      # 4. Instantiate the subclass
    exit_code = appctxt.run()                   # 5. Invoke run()
    sys.exit(exit_code)

The important steps are highlighted as comments. If they look daunting to you, don't worry. They're the only boilerplate that's required. In the middle of the code, you can see that a window is being created, resized and then shown.

A more complicated example

We will now create a more interesting example: An app that displays famous quotes from the internet. Here's what it looks like:

Before you can run it, you need to install the Python requests library. To do this, type in the following command:

pip install requests

The source code of the new app lies in main_2.py. To tell fbs about this file, please change the main_module setting in base.json to "src/main/python/main_2.py". Then, you can do python -m fbs run (or ... freeze etc.) as before.

The new app uses the following code to fetch quotes from the internet:

def _get_quote():
    response = requests.get('https://talaikis.com/api/quotes/random/')
    return response.json()['quote']

You can see that it uses the requests library we just installed above. Feel free to open https://talaikis.com/api/quotes/random/ in the browser to get a feel for its data.

The app follows the same basic steps as before. It defines an application context with a run() method that ends in return self.app.exec_():

class AppContext(ApplicationContext):
    def run(self):
        ...
        return self.app.exec_()
    ...

It then instantiates this application context and invokes run():

if __name__ == '__main__':
    appctxt = AppContext()
    exit_code = appctxt.run()
    sys.exit(exit_code)

What's different is what happens in between. First, let's look at the implementation of run():

def run(self):
    stylesheet = self.get_resource('styles.qss')
    self.app.setStyleSheet(open(stylesheet).read())
    self.window.show()
    return self.app.exec_()

The first line uses get_resource(...) to obtain the path to styles.qss. This is a QSS file, Qt's equivalent to CSS. The next line reads its contents and sets them as the stylesheet of self.app.

fbs ensures that get_resource(...) works both when running from source (i.e. during python -m fbs run) and when running the compiled form of your app. In the former case, the returned path is in src/main/resources. In the latter, it will be in your app's installation directory. fbs handles the corresponding details transparently.

The last but one line accesses self.window. This is defined as follows:

@cached_property
def window(self):
    return MainWindow()

You can use @cached_property to define the components that make up your app. The way it works is that the first time self.window is accessed, return MainWindow() is executed. Further accesses then cache the value and return it without re-executing the code.

The above approach is extremely useful: In your ApplicationContext, define a @cached_property for each component (a window, a database connection, etc.). If it requires other objects, access them as properties. For example, if the window requires the database because it displays information from it, then its @cached_property would access self.database. If you connect the parts of your application in this centralised way, then it is extremely easy to see how they work together.

The final bit of code is the definition of MainWindow. It sets up the text field for the quote and the button. When the button is clicked, it changes the contents of the text field using _get_quote() above. You can find the corresponding code in main_2.py.

As already mentioned, you can use python -m fbs run to run the new app. But here's what's really cool: You can also do python -m fbs freeze and ... installer to distribute it to other computers. fbs includes the requests dependency and the styles.qss file automatically.

Summary

fbs lets you use Python and Qt to create desktop applications for Windows, Mac and Linux. It can create installers for your app, and automatically handles the packaging of third-party libraries and data files. These things normally take weeks to figure out. fbs gives them to you in minutes instead.

Where to go from here

fbs's Manual explains the technical foundation of the steps in this tutorial. Read it to find out more about fbs's required directory structure, dependency management, handling of data files, custom build commands, API and more.

If you have not used PyQt before: It's the library that allowed us in the above examples to use Qt (a GUI framework) from Python. fbs's contribution is not to combine Python and Qt. It's to make it very easy to package and deploy PyQt-based apps to your users' computers. For examples of what PyQt can do, take a look here and here.

Feel free to share the link to this tutorial! If you are not yet on fbs's mailing list and want to be notified as it evolves, sign up here.