How the Model View Controller Architecture Works MVC Explained

New models can be created by implementing the standard interface provided by QAbstractItemModel. In the Creating New Models section, we demonstrate this by creating a convenient ready-to-use model for holding lists of strings. To obtain a model index, we specify the row number, column number (zero for the first column), and the appropriate model index for the parent of all the items that we want.

The controller also feeds data to the view component in response to user requests. In addition, the controller interfaces with the model component, which sends updated data to the view element. The view component is concerned only with rendering the data provided by the controller, model or both.

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We construct a table view to display the contents of the model, and this will use the custom delegate for editing. QAbstractItemDelegate is the abstract base class for delegates in the model/view framework. The default delegate implementation is provided by QStyledItemDelegate, and this is used as the default delegate by Qt’s standard views. However, QStyledItemDelegate and QItemDelegate are independent alternatives to painting and providing editors for items in views. The difference between them is that QStyledItemDelegate uses the current style to paint its items.

• This blog post defines the concept of a Model-View-Controller (MVC) software design pattern and does a basic example Model-View-Controller in JavaScript/HTML/CSS.
• After changing the string list, it calls endInsertRows() to complete the operation and inform other components that the dimensions of the model have changed, returning true to indicate success.
• Model indexes provide temporary references to pieces of information, and can be used to retrieve or modify data via the model.
• Using this model, we can show how to set up a model for use with ready-made views, and explore how to manipulate data using model indexes.
• The canFetchMore() function checks if the parent has more data available and returns true or false accordingly.

These four functions must be implemented in all types of model, including list models (QAbstractListModel subclasses) and table models (QAbstractTableModel subclasses). The separation of functionality between the model/view components allows models to be created that can take advantage of existing views. This approach lets us present data from a variety of sources using standard graphical user interface components, such as QListView, QTableView, and QTreeView. A selection is created by specifying a model, and a pair of model indexes to a QItemSelection. This uses the indexes to refer to items in the given model, and interprets them as the top-left and bottom-right items in a block of selected items.

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The text stored in each item is retrieved using the model’s data() function. We specify the model index and the DisplayRole to obtain data for the item mvc developer in the form of a string. The diagram shows a representation of a basic table model in which each item is located by a pair of row and column numbers.