easy-mvp 0.2.0

Construct MVP PyQt5 application easily

easy_mvp

Description

easy_mvp is a package that makes it easy to build desktop applications using MVP pattern, Python and PyQt5. This is achieved by using a set of classes and practices similar to those used in the Android framework.

The basic idea behind this package is to open a presenter from another presenter and that the new presenter fills the window for complete. This is similar to Android applications, which when opening a new Activity, they replace the old one with the new one. If the Back button is pressed, then the new Activity is removed and the old one reappears on the screen. This gives the impression that there is a stack of Activity.

In addition, easy_mvp offers the possibility of doing the above in more than a window, since desktop applications are very different to Android apps.

Installation

To install this package you need to have Python installed in your system. Then you can run this command to install this package:

pip install easy_mvp

Explaining the mechanism

The following explanations are reflected in demo.py program.

The application model created by easy_mvp is like this:

The ApplicationManager class is the entry point of the program. This class is the one that knows the windows, creates them and destroys them. Each window holds a stack of presenters. In this way it is implemented the same behavior that Android applications have. Class Intent is used to transition from one presenter to another, regardless of whether the new presenter is started in a new window.

The behavior of the windows is represented as follows:

As you can see the window has a stack of presenters, the which are attached to their views, therefore all the presenters must possess a view. Again we can see that the class Intent is the one that allows to add a new pair of presenter-view to the window stack. For this mechanism to work, the presenter classes must inherit from the AbstractPresenter class.

AbstractPresenter has several methods to open new presenters, close the current presenter and to handle certain flows within the application, such as when a presenter is going to be initialized, hidden, or closed.

The flow of events in a class that inherits from AbstractPresenter is like this:

The _on_initialize method is the first method called in the AbstractPresenter class. Here the instance variables of the presenter must be initialized. Also, you must create the instance of the view that corresponds to the presenter. Once created, the view instance must be set with the _set_view(view) method, from this way the view is made accessible to the rest of the classes in easy_mvp environment. The view can be obtained with the view property or get_view method of AbstractPresenter, if it was set by _set_view(view) first.

The on_view_shown method is called just after the presenter view is displayed in the graphical interface. In this method the data should be loaded, and the tables and forms filled.

If on the presenter whose view is visible, _open_other_presenter is called then another presenter will be created, and this presenter will go to the top of the stack of presenters, and its view will be the only one visible in the graphical interface. The view of presenter that called _open_other_presenter will no longer be visible. Before this last occurs, the calling presenter will receive control of the program with the method on_view_covered.

If now the top presenter calls _close_this_presenter, then the presenter view just below it will be visible again, and the presenter will receive control of the main thread via on_view_discovered. In this method the view should be updated due to some change in the model.

When the presenter at the top of the stack calls _close_this_presenter receives the control with the on_closing_presenter method. In this method resources should be released and observers removed. After the call to on_closing_presenter the presenter and the view of the presenter will be removed, and it will happen what it has been explained previously. It should be noted that if the presenter who closes is the only one that exists in the entire application, that is, there is only one window, and it owns only a presenter then the application will close with the status code 0. To close the program with different code, use the exit_app method of AbstractPresenter.

Receiving data from presenters

A presenter can receive data from another presenter that it has created, if the second one is closed using the _close_this_presenter_with_result(result_data: dict, result: str = Intent.NO_RESULT) method. In this way, the presenter that is below in the stack receives control of the program via on_view_discovered_with_result(action: str, data: dict, result: str) instead of on_view_discovered. The action parameter is the action that was passed to the Intent when it was ordered to open the new presenter. The result_data is a Python dictionary that the presenter who was on top can pass through _close_this_presenter_with_result(result_data: dict, result: str = Intent.NO_RESULT). The result string can be used to tell the below presenter what happened on top presenter. In this way the below presenter can take different decisions depending on the result returned by top presenter.

Managing global data

Data can be created to be accessible throughout the entire application. This is accomplished with the set_global_data(key: str, data) and get_global_data(key: str) methods of AbstractPresenter. You can also check if a global data exists with the method has_global_data(key: str), which returns True if it exists and False otherwise.

Knowing Intent in depth

As explained Intent is what makes it possible to open new presenters. You can specify that the new presenter must be opened on a new window using use_new_window(use_new_window: bool = False). You can also specify that if a new window is to be opened, then make it modal or not with the method use_modal(self, modal: bool = False).

An intent can be specified with an action with set_action(action: str), like so the new presenter may behave differently depending on the action received.

Intent also allows data to be passed to a new presenter via set_data(data: dict). To see examples of how Intent is used, check out the demo.py program.

Acting when user closes window

If the user clicks the close window button then all presenters in the presenter stack of the window will receive the on_window_closing(self) call. The first presenter to receive the call will be the one which is on the stack top, the next to receive the call will be the below presenter. This flow of calls will occur all the way down through the window stack. When all presenters have executed on_window_closing(self) then the window will be closed. If the window that is being closing has child windows, then all its children will receive the on_window_closing(self) calls in the same way the parent window received it.

This method is useful to close database connections, close files and stop threads. All you must close goes here.

Customize window title

Every presenter can change the window title. This is useful because each presenter will do a different task, and therefore you would like to change the title of the window depending on it.

You can reimplement the method get_default_window_title(self) to set a custom window title. You only have to set return 'My custom window title' in the method's body. This method will be called before the presenter receives the on_view_show, on_view_discovered and on_view_discovered_with_result calls. By default, this method returns the 'No Title, reimplement get_default_window_title' string.

But if you want more power on changing the window title you can use the _set_window_title(self, window_title: str) to immediately change it. After calling this method the window title can be replaced automatically if the presenter who set it is popped, or if a new presenter is added on top. This will happen because of the calls to get_default_window_title(self) on below presenter or on the new presenter respectively, during the easy-mvp event flow.

Setting application name and window Icon

You can set the application name and Window Icon by passing this information to ApplicationManager constructor:

manager = ApplicationManager(
    app_name='easy_mvp demo',
    window_icon_path='./demo/view/ui/assets/icon.png'
)

This way the operating system will know the name of your app and its window icon.