QOlm

qolm::QOlm object based on QAbstractListModel that provide a list of QObject based class to qml and c++. The model dynamically update views by reacting to insert, remove, move operations.

🚀 Overview

QOlm is based on QAbstractListModel, and behave as a list of custom QObject. QOlmBase is detail implementation to provide signals and slots that moc can handle. Since moc isn't working with template class.

🔨 Build and integrate

• QOlm is the main target. It has an alias QOlm::QOlm.
• It come with unit tests QOlm_Tests
• It come with examples QOlm_Examples

CMake add_subdirectory

Copy QOlm source in your project, and simply call add_subdirectory to enable QOlm::QOlm target

add_subdirectory(path/to/qolm-src)
target_link_libraries(MyTarget PRIVATE QOlm::QOlm)

CMake FetchContent

Add the following code snippet to your CMakelists.txt. This will download and build QOlm with MyTarget.

CMake 3.14 is required, CMake 3.17 is recommended to take advantage of pch headers.

# ...
include(FetchContent)
FetchContent_Declare(
    QOlm
    GIT_REPOSITORY "https://github.com/OlivierLDff/QOlm"
    GIT_TAG        "master"
)
# ...
FetchContent_MakeAvailable(QOlm)
# ...

target_link_libraries(MyTarget PRIVATE QOlm::QOlm)

CPM.cmake

Include QOlm with CPM.cmake. CMake 3.14 is required because CPM use FetchContent under the hood.

include(cmake/CPM.cmake)
CPMAddPackage(
  NAME QOlm
  GIT_REPOSITORY "https://github.com/OlivierLDff/QOlm"
  GIT_TAG "master"
)
target_link_libraries(MyTarget PRIVATE QOlm::QOlm)

📦️ Install

QOlm can be installed with:

# configure
cmake -DQOLM_ENABLE_INSTALL=ON ..

# build
cmake --build . --target QOlm --config "Release

# install
cmake --install . [--prefix <install-dir>] 

Install tree folder should look like this:

prefix/
 ├─include/
 │  └─QOlm/
 │     ├─QOlm.hpp
 │     └─Details/
 │        ├─Export.hpp
 │        └─QOlmBase.hpp
 └─lib/
    ├─QOlm.lib
    └─cmake/
       └─QOlm/
          ├─QOlmConfig.hpp
          ├─QOlmConfigVersion.hpp
          └─QOlmTargets.cmake

Prefix folder can be overridden

• with CMAKE_INSTALL_PREFIX at configure step.
• with --prefix <install-dir> at install step.

You can then include QOlm into another cmake project by using find_package(QOlm) .

✅ Execute tests

If QOLM_ENABLE_TESTS is on then you can execute unit test.

cmake -DQOLM_ENABLE_TESTS=ON ..
cmake --build . --target QOlm_Tests --config "Release"
ctest -C "Release" .

To only execute certain test in as a developer:

./tests/QOlm_Tests --gtest_filter=TestCaseRegEx*

🎉 Execute Example

The option QOLM_ENABLE_EXAMPLES should be turned on.

cmake -DQOLM_ENABLE_EXAMPLES=ON ..
cmake --build . --target QOlm_Examples --config "Release"
./examples/QOlm_Examples

🔧 Additional CMake flags

Since CMake is using FetchContent functionality, you can add flags to understand what is going on. The library also require package Qt, so you need to indicate where Qt SDK is installed. Provide the path with CMAKE_PREFIX_PATH.

cmake
# Log output during download of dependencies
-DFETCHCONTENT_QUIET=OFF
# Avoid that dependencies source gets pulled at each cmake command
# Very useful when developping on dependencies too.
-DFETCHCONTENT_UPDATES_DISCONNECTED=ON
-DCMAKE_PREFIX_PATH=/Path/To/Qt
..

📌 Dependencies

QOlm is fetching quite a few external libraries. Source of those libraries can be customize. Variables are in form _REPOSITORY and _TAG

• Qt Core Qml.

Dependencies of tests

• GTEST : Provide gtest library for unit tests.
• Qt Tests.

C++ Getting started

Most of the time you want to store more than just QObject type, so create your custom type.

#include <QtCore/QObject>

class Foo : public QObject
{
    Q_OBJECT
public:
    Foo(QObject* parent = nullptr) : QObject(parent) {}

    int foo = 0;
};

Then use a QOlm based object with class inheritance or as a typedef.

#include <Foo.hpp>
#include <QOlm/QOlm.hpp>

// Declare type
using FooList = qolm::QOlm<Foo>;

// Or create custom class
class FooList : public qolm::QOlm<Foo>
{
    Q_OBJECT
public:
    Foo(QObject* parent = nullptr,
        const QList<QByteArray> & exposedRoles = {},
        const QByteArray & displayRole = {}):
    qolm::QOlm<Foo>::(parent, exposedRoles, displayRole)
    {
    }
};

Then simply use it as a regular list.

Insert elements

The object provide multiple way to insert an object in the list:

• append : Add an object at the end of the list.
• prepend : Add an object at the beginning of the list.
• insert : Insert object at requested offset.

Those three functions can also take a QList<_Object*> as a parameter entry to insert multiple object at once.

FooList list;
Foo foo1;
Foo foo2;
Foo foo3;
Foo foo4;

// {foo1}
list.append(&foo1);

// {foo2, foo1}
list.prepend(&foo2);

// {foo2, foo1, foo3}
list.append(&foo3);

// {foo2, foo4, foo1, foo3}
list.insert(1, &foo4);

Remove elements

To remove an item, simply call the remove function, either with a pointer to the _Object* , or with the index of the object at which you want to remove.

All elements can also be removed using clear function.

FooList list;
Foo foo1;
Foo foo2;
Foo foo3;
Foo foo4;
list.append({&foo1, &foo2, &foo3, &foo4});

// { &foo1, &foo2, &foo4 }
list.remove(&foo3);
// { &foo1, &foo2 }
list.remove(2);
// Remove all elements.
list.clear();

Move elements

Elements can be moved within the list, without changing the list size.

• move from object at index from to index to.
• moveUp: Move object at index index to index-1. This function make sense when seeing the list in a ListView for example. It move the item to previous index.
• moveDown: Move object from index to index+1. This function make sense in a ListView in a column. It move the item to next index.
• moveNext: alias of moveDown.
• movePrevious: alias of moveUp.

FooList list;
Foo foo1;
Foo foo2;
Foo foo3;
Foo foo4;
list.append({&foo1, &foo2, &foo3, &foo4});

// { &foo1, &foo3, &foo4, &foo2 }
list.move(1, 3);

// { &foo2, &foo1, &foo3, &foo4 }
list.move(3, 0);

// { &foo2, &foo3, &foo1, &foo4 }
list.movePrevious(2);

// { &foo2, &foo3, &foo4, &foo1 }
list.moveNext(2);

Access element and get index

Multiple accessors can be used to get data.

• get : Get pointer to the _Object* at index.
• indexOf : Get the index from a _Object*
• contains : Get if a _Object* is present.
• size: Give the number of objects in the model
• empty : True if model is empty.

Object ownership

The library follow qt ownership rules. So when inserting an object without parent, the list take ownership of that object. When the same object is removed it will be deleteLater.

FooList list;
// list take ownership on new Foo
list.append(new Foo());
// Since FooList have ownership on the foo at index 0, it call deleteLater on it. No need to worry about memory management.
list.remove(0);

Observe list

Observe as QAbstractItemModel

The qolm::QOlm derived object can be observe for insertion and deletion like any qt model.

• rowsAboutToBeInserted
• rowsAboutToBeMoved
• rowsAboutToBeRemoved
• rowsInserted
• rowsMoved
• rowsRemoved

But those signals are not very convenient to use as a end user. That's why QOlm provide other way to observe the list.

Observe thru signals

qolm::QOlmBase provide basic signal to react to QObject insert/remove/move operation.

• objectInserted(QObject* object, int index)
• objectRemoved(QObject* object, int index)
• objectMoved(QObject* object, int from, int to)

They are call when the model can safely be iterated. You can simply retrieve a correct pointer by using qobject_cast<_Object*>(object).

Function override observe.

Sometime it can be useful to do some processing before the whole world gets notify about our object operation. This method is only available if you define a custom list type.

#include <Foo.hpp>
#include <QOlm/QOlm.hpp>

class FooList : public qolm::QOlm<Foo>
{
    Q_OBJECT
public:
    FooList(QObject* parent = nullptr,
        const QList<QByteArray> & exposedRoles = {},
        const QByteArray & displayRole = {}):
    QOlm<Foo>(parent, exposedRoles, displayRole)
    {
    }

protected:
    void onItemAboutToBeInserted(_Object* item, int row) override
    {
        // Item is not yet inserted, do some preinsert operation on it.
    }
    void onItemInserted(_Object* item, int row) override
    {
        // Item just got inserted, but no callback/signal have been called yet.
    }
    void onItemAboutToBeMoved(_Object* item, int src, int dest) override
    {
        // Item haven't move yet, and no callback/signal have been called yet
    }
    void onItemMoved(_Object* item, int src, int dest) override
    {
        // Item have been moved. No Callback/Signal have been called yet.
    }
    void onItemAboutToBeRemoved(_Object* item, int row) override
    {
        // Item isn't removed yet, and no callback/signal have been called yet
    }
    void onItemRemoved(_Object* item, int row) override
    {
        // Item have been removed. Callback/Signal have been called
    }
};

Observe with callback

QOlm provide lambda connection with already qobject_cast objects. This is the preferred and easier way to observe the list

FooList list;

// Preferred API, safer to use when giving a context
list.onInserted(&list, [](Foo* foo, int index){});
list.onInserted(&list, [](Foo* foo){});
list.onRemoved(&list, [](Foo* foo, int index){});
list.onRemoved(&list, [](Foo* foo){});
list.onMoved(&list, [](Foo* foo, int from, int to){});

// Should only be used when your callback doesn't require any context
list.onInserted([](Foo* foo, int index){});
list.onInserted([](Foo* foo){});
list.onRemoved([](Foo* foo, int index){});
list.onRemoved([](Foo* foo){});
list.onMoved([](Foo* foo, int from, int to){});

When connecting without any receiver, this list is used as the context.

Iterator

QOlm is compatible with modern iterator, you can simply do:

FooList list;
for(const auto* foo : list)
{
    //foo->getFoo()
}
for(auto* foo : list)
{
    //foo->setFoo(12)
}

Getting Started Qml

The same api as the c++ work in qml. Every Q_PROPERTY are exposed as role, and another role qtObject allow to access the QObject*.

For the following example to work Foo and FooList need to be registered to the qml system.

import QtQuick 2.0
import MyFoo 1.0

ListView {
    width: 180; height: 200
    FooList { id: _fooList }

    model: _fooList
    delegate: Text
    {
        // Access role qtObject and cast it to our type
        property Foo fooObj : model.qtObject
        text: index + ": " +
            fooObj.foo + // Access via casted object
            + ", " +
            foo // Access via role
    }

    Component.onCompleted:
    {
        _fooList.append(new Foo())
        _fooList.insert(1, new Foo())
        _fooList.prepend(new Foo())
    }
}

If you need to filter exposed roles, then use the constructor arguments. Same to set a display role.

//QOlm(QObject* parent = nullptr,
//   const QList<QByteArray> & exposedRoles = {},
//   const QByteArray & displayRole = {})

// The following code expose foo as exposedRoles, and foo as Qt::DisplayRole
FooList list(nullptr, {"foo"}, "foo");

It is recommended to only expose role that are required for QSortFilterProxyModel subclass. And use native signal to property for property that often change.

Authors

• Olivier LDff