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/****************************************************************************
**
** Copyright (C) 2015 The Qt Company Ltd.
** Contact: http://www.qt.io/licensing/
**
** This file is part of the documentation of the Qt Toolkit.
**
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****************************************************************************/
/*!
\title Enginio C++ Examples - Todos
\example todos-cpp
\brief The Todo example shows how to use the \l {EnginioModelCpp}{EnginioModel} with Qt Widgets.
\ingroup enginio-examples
\inmodule enginio-qt
In this example, a simple list of objects is displayed in a \l QListView.
Each item in the list is a "To Do" object which can be "done" or "not yet done".
Todos can be added, removed, or altered.
\image todo-example.png
In this simple schema the objects will have two properties that are added
to the default properties (such as creation date which always exists):
a string "title" and a bool "completed". The object type will be created
when a call to create, or in this case EnginoModel::append(), is made.
A todo object will look like this (in JSON):
\code
{
"title": "Buy Milk",
"completed": false
}
\endcode
The first step is to create a TodosModel which inherits \l {EnginioModelCpp}{EnginioModel},
and defines the main roles which will be used. As we are interested in the To Do \c title
and the \c completed information we need to define these two roles.
\snippet todos-cpp/todosmodel.h definition
By default, views (for example \l QListView) use the \l{Qt::ItemDataRole} role to display or edit the content.
The newly created \l{EnginioModelCpp}{EnginioModel} is empty and defines basic roles. Most roles are created
dynamically, based on the JSON datastructure. They have no predefined value in the \l Qt::ItemDataRole enum.
\l{EnginioModelCpp}{EnginioModel} automatically populates itself as soon as the
\l{EnginioModel::query}{query} and \l{EnginioModel::client}{client} properties have been set.
When the data is downloaded, the model resets itself, and sets up the internal data cache and roles names.
\l{EnginioModelCpp}{EnginioModel} guesses the role names based on heuristics. It may be wrong if not all
objects received from the backend have exactly the same structure. For example, a property can be missing
in certain objects. To protect against such cases, we overload \l{EnginioModel::roleNames()}{roleNames()}.
Overriding \l{EnginioModel::roleNames()}{roleNames()} can also be used to match default Qt roles to the named
ones.
\snippet todos-cpp/todosmodel.cpp roleNames
In this example we map the \l Qt::DisplayRole and \l Qt::EditRole to the \c title property in the JSON.
This way the right string is shown by default and editing works as expected.
Remember to always call the base class implementation to avoid situations in which the internal cache is not in sync.
By default \l {EnginioModelCpp}{EnginioModel} operates on \l{QJsonValue}, and that is
what the \l{EnginioModel::data()}{data()} function returns inside the \l QVariant, but standard
views, such as \l QListView, use predefined roles which do not map directly to our roles.
That is why we need to write a mapping between them:
\snippet todos-cpp/todosmodel.cpp data
As we have our model defined, we need to create an instance of \l EnginioClient:
\snippet todos-cpp/mainwindow.cpp client
It is used by the model to connect to the Enginio backend. Next we need to construct
and configure our model too. The configuration is based on two steps, assigning
an \l EnginioClient instance and by creating a query.
\snippet todos-cpp/mainwindow.cpp model
The model has to be assigned to a view. In our case it is a \l QListView.
\snippet todos-cpp/mainwindow.cpp assignModel
To make the application fully functional, a way to add and remove "To Dos" is needed.
To do so, we need to connect the correct buttons to slots for adding a new item:
\snippet todos-cpp/mainwindow.cpp appendItem
and for removing it:
\snippet todos-cpp/mainwindow.cpp removeItem
*/
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