本文小编为大家详细介绍“C++数据模型怎么应用在QML委托代理机制中”，内容详细，步骤清晰，细节处理妥当，希望这篇“C++数据模型怎么应用在QML委托代理机制中”文章能帮助大家解决疑惑，下面跟着小编的思路慢慢深入，一起来学习新知识吧。
定义数据模型
定义的C++数据模型和Qt-Widget中定义的数据模型相同。模型主要用来存储本地图片的ID的对应的图片地址。
实现如下:
//picturemodel.h
#ifndef PICTUREMODEL_H
#define PICTUREMODEL_H
#include <memory>
#include <vector>
#include <QAbstractListModel>
#include <QUrl>
class Picture
{
public:
Picture(const QString & filePath = "")
{
mPictureUrl = QUrl::fromLocalFile(filePath);
}
Picture(const QUrl& fileUrl)
{
mPictureUrl = fileUrl;
}
int pictureId() const
{
return mPictureId;
}
void setPictureId(int pictureId)
{
mPictureId = pictureId;
}
QUrl pictureUrl() const
{
return mPictureUrl;
}
void setPictureUrl(const QUrl &pictureUrl)
{
mPictureUrl = pictureUrl;
}
private:
int mPictureId; // 图片ID
QUrl mPictureUrl; //图片的地址
};
class PictureModel : public QAbstractListModel
{
Q_OBJECT
public:
//自定义每个元素的数据类型
enum Roles {
UrlRole = Qt::UserRole + 1,
FilePathRole
};
PictureModel(QObject* parent = 0);
//向数据模型中添加单个数据
QModelIndex addPicture(const Picture& picture);
Q_INVOKABLE void addPictureFromUrl(const QUrl& fileUrl);
//模型的行数
int rowCount(const QModelIndex& parent = QModelIndex()) const override;
//获取某个元素的数据
QVariant data(const QModelIndex& index, int role) const override;
//删除某几行数据
Q_INVOKABLE bool removeRows(int row, int count, const QModelIndex& parent = QModelIndex()) override;
//每个元素类别的名称
QHash<int, QByteArray> roleNames() const override;
//加载用户图片
Q_INVOKABLE void loadPictures();
//清空模型的中的数据,但不移除本地文件数据
void clearPictures();
public slots:
//清空模型,删除本地文件中的数据
void deleteAllPictures();
private:
void resetPictures();
bool isIndexValid(const QModelIndex& index) const;
private:
std::unique_ptr<std::vector<std::unique_ptr<Picture>>> mPictures;
};
#endif // PICTUREMODEL_H//picturemodel.cpp
#include "picturemodel.h"
#include <QUrl>
using namespace std;
PictureModel::PictureModel(QObject* parent) :
QAbstractListModel(parent),
mPictures(new vector<unique_ptr<Picture>>())
{
}
QModelIndex PictureModel::addPicture(const Picture& picture)
{
int rows = rowCount();
beginInsertRows(QModelIndex(), rows, rows);
unique_ptr<Picture>newPicture(new Picture(picture));
mPictures->push_back(move(newPicture));
endInsertRows();
return index(rows, 0);
}
void PictureModel::addPictureFromUrl(const QUrl& fileUrl)
{
addPicture(Picture(fileUrl));
}
int PictureModel::rowCount(const QModelIndex& /*parent*/) const
{
return mPictures->size();
}
QVariant PictureModel::data(const QModelIndex& index, int role) const
{
if (!isIndexValid(index))
{
return QVariant();
}
const Picture& picture = *mPictures->at(index.row());
switch (role) {
//展示数据为图片的名称
case Qt::DisplayRole:
return picture.pictureUrl().fileName();
break;
//图片的URL
case Roles::UrlRole:
return picture.pictureUrl();
break;
//图片地址
case Roles::FilePathRole:
return picture.pictureUrl().toLocalFile();
break;
default:
return QVariant();
}
}
bool PictureModel::removeRows(int row, int count, const QModelIndex& parent)
{
if (row < 0
|| row >= rowCount()
|| count < 0
|| (row + count) > rowCount()) {
return false;
}
beginRemoveRows(parent, row, row + count - 1);
int countLeft = count;
while(countLeft--) {
const Picture& picture = *mPictures->at(row + countLeft);
}
mPictures->erase(mPictures->begin() + row,
mPictures->begin() + row + count);
endRemoveRows();
return true;
}
QHash<int, QByteArray> PictureModel::roleNames() const
{
QHash<int, QByteArray> roles;
roles[Qt::DisplayRole] = "name";
roles[Roles::FilePathRole] = "filepath";
roles[Roles::UrlRole] = "url";
return roles;
}
void PictureModel::loadPictures()
{
beginResetModel();
endResetModel();
}
void PictureModel::clearPictures()
{
resetPictures();
}
void PictureModel::resetPictures()
{
beginResetModel();
mPictures.reset(new vector<unique_ptr<Picture>>());
endResetModel();
return;
}
void PictureModel::deleteAllPictures()
{
resetPictures();
}
bool PictureModel::isIndexValid(const QModelIndex& index) const
{
if (index.row() < 0
|| index.row() >= rowCount()
|| !index.isValid()) {
return false;
}
return true;
}定义C++数据模型的时候有几点需要注意:
1.如果想在QML中访问模型的某个方法的话需要在方法声明的时候添加Q_INVOKABLE宏
Q_INVOKABLE void addPictureFromUrl(const QUrl& fileUrl);
2.在QML中通过每个元素类别的名称来进行访问，对应的类别名称的定义如下:
QHash<int, QByteArray> PictureModel::roleNames() const
{
QHash<int, QByteArray> roles;
roles[Qt::DisplayRole] = "name";
roles[Roles::FilePathRole] = "filepath";
roles[Roles::UrlRole] = "url";
return roles;
}定义图片缓存器
由于数据模型中包含图片数据，为了便于在QML中访问图片资源，添加图片缓存器。缓存器继承自QQuickImageProvider。对应的实现如下所示:
//PictureImageProvider.h
#ifndef PICTUREIMAGEPROVIDER_H
#define PICTUREIMAGEPROVIDER_H
#include <QQuickImageProvider>
#include <QCache>
class PictureModel;
class PictureImageProvider : public QQuickImageProvider
{
public:
static const QSize THUMBNAIL_SIZE;
PictureImageProvider(PictureModel* pictureModel);
//请求图片
QPixmap requestPixmap(const QString& id, QSize* size, const QSize& requestedSize) override;
//获取缓存
QPixmap* pictureFromCache(const QString& filepath, const QString& pictureSize);
private:
//数据模型
PictureModel* mPictureModel;
//图片缓存容器
QCache<QString, QPixmap> mPicturesCache;
};
#endif // PICTUREIMAGEPROVIDER_H//PictureImageProvider.cpp
#include "PictureImageProvider.h"
#include "PictureModel.h"
//全屏显示
const QString PICTURE_SIZE_FULL = "full";
//缩略显示
const QString PICTURE_SIZE_THUMBNAIL = "thumbnail";
//缩略显示的尺寸
const QSize PictureImageProvider::THUMBNAIL_SIZE = QSize(350, 350);
PictureImageProvider::PictureImageProvider(PictureModel* pictureModel) :
QQuickImageProvider(QQuickImageProvider::Pixmap),
mPictureModel(pictureModel),
mPicturesCache()
{
}
QPixmap PictureImageProvider::requestPixmap(const QString& id, QSize* /*size*/, const QSize& /*requestedSize*/)
{
QStringList query = id.split('/');
if (!mPictureModel || query.size() < 2) {
return QPixmap();
}
//第几个图片数据
int rowId = query[0].toInt();
//显示模式是缩略显示还是全屏显示
QString pictureSize = query[1];
QUrl fileUrl = mPictureModel->data(mPictureModel->index(rowId, 0), PictureModel::Roles::UrlRole).toUrl();
return *pictureFromCache(fileUrl.toLocalFile(), pictureSize);
}
QPixmap* PictureImageProvider::pictureFromCache(const QString& filepath, const QString& pictureSize)
{
QString key = QStringList{ pictureSize, filepath }
.join("-");
//不包含图片的时候创建新的缓存
QPixmap* cachePicture = nullptr;
if (!mPicturesCache.contains(key))
{
QPixmap originalPicture(filepath);
if (pictureSize == PICTURE_SIZE_THUMBNAIL)
{
cachePicture = new QPixmap(originalPicture
.scaled(THUMBNAIL_SIZE,
Qt::KeepAspectRatio,
Qt::SmoothTransformation));
}
else if (pictureSize == PICTURE_SIZE_FULL)
{
cachePicture = new QPixmap(originalPicture);
}
mPicturesCache.insert(key, cachePicture);
}
//包含的时候直接访问缓存
else
{
cachePicture = mPicturesCache[key];
}
return cachePicture;
}初始化QML引擎
在QML引擎初始化的时候添加对应的数据模型和图片缓存器，对应的实现如下:
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include "picturemodel.h"
#include "PictureImageProvider.h"
int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);
PictureModel pictureModel;
QQmlApplicationEngine engine;
QQmlContext* context = engine.rootContext();
//添加数据模型和图片缓存器
context->setContextProperty("pictureModel", &pictureModel);
//图片Provider的ID是"pictures"
engine.addImageProvider("pictures", new PictureImageProvider(&pictureModel));
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
if (engine.rootObjects().isEmpty())
return -1;
return app.exec();
}QML中访问C++数据模型
在QML中通过数据模型访问数据，通过图片缓存器访问对应的图片资源，对应的实现如下:
//main.qml
import QtQuick 2.8
import QtQuick.Dialogs 1.2
import QtQuick.Controls 2.0
import QtQuick.Layouts 1.3
import QtQuick.Window 2.2
Window {
visible: true
width: 640
height: 480
title: qsTr("QML-MVC")
RowLayout {
id:tool_layout
//添加图片的按钮
ToolButton {
background: Image {
source: "qrc:/image/photo-add.svg"
}
onClicked: {
dialog.open()
}
}
//删除图片的按钮
ToolButton {
background: Image {
source: "qrc:/image/photo-delete.svg"
}
onClicked: {
pictureModel.removeRows(pictureListView.currentIndex,1)
}
}
}
//网格视图
GridView {
id: pictureListView
model: pictureModel
anchors.top:tool_layout.bottom
width: parent.width;
height: parent.height - tool_layout.height
anchors.leftMargin: 10
anchors.rightMargin: 10
cellWidth : 300
cellHeight: 230
//对应的每个元素的代理
delegate: Rectangle {
width: 290
height: 200
color: GridView.isCurrentItem?"#4d9cf8":"#ffffff" //选中颜色设置
Image {
id: thumbnail
anchors.fill: parent
fillMode: Image.PreserveAspectFit
cache: false
//通过缓存器访问图片
//image://pictures/访问器的ID
//index + "/thumbnail" 图片索引和显示模式
source: "image://pictures/" + index + "/thumbnail"
}
//访问图片的名称
Text {
height: 30
anchors.top: thumbnail.bottom
text: name
font.pointSize: 16
anchors.horizontalCenter: parent.horizontalCenter
}
//鼠标点击设置当前索引
MouseArea{
anchors.fill: parent
onClicked: {
pictureListView.currentIndex = index;
}
}
}
}
//图片选择窗口
FileDialog {
id: dialog
title: "Select Pictures"
folder: shortcuts.pictures
onAccepted: {
var pictureUrl = dialog.fileUrl
pictureModel.addPictureFromUrl(pictureUrl)
dialog.close()
}
}
}显示效果如下图所示: