QT委托代理機(jī)制之Model?View?Delegate使用方法詳解

更新時(shí)間：2022年08月25日 10:26:09 作者：碼農(nóng)飛飛

這篇文章主要介紹了QT委托代理機(jī)制之Model?View?Delegate的使用方法，對(duì)大家的學(xué)習(xí)或者工作具有一定的參考學(xué)習(xí)價(jià)值，需要的朋友們下面隨著小編來一起學(xué)習(xí)學(xué)習(xí)吧

之前的一篇文章中介紹過QT的委托代理機(jī)制，那時(shí)候由于理解的比較淺就簡單的給了一個(gè)例子。最近又做了一部分相關(guān)的工作，發(fā)現(xiàn)之前的理解有點(diǎn)問題。這里就詳細(xì)的介紹一下QT的委托代理機(jī)制的用法，希望對(duì)大家有幫助。

Model-View-Delegate機(jī)制可以簡單的理解為將本地的一些數(shù)據(jù)以特定的UI形式呈現(xiàn)出來。常見的數(shù)據(jù)結(jié)構(gòu)包括列表數(shù)據(jù)(list)、表格數(shù)據(jù)(table)、樹狀數(shù)據(jù)(tree)，分別對(duì)應(yīng)著QT中的QListView、QTableView、QTreeView控件。本地?cái)?shù)據(jù)和視圖代理之間的關(guān)系如下圖所示:

數(shù)據(jù)模型中的數(shù)據(jù)來源可以是本地的XML文件、JSON文件、二進(jìn)制數(shù)據(jù)，也可以數(shù)據(jù)庫中的數(shù)據(jù)表。這些數(shù)據(jù)源中的數(shù)據(jù)按照一定的結(jié)構(gòu)加載到對(duì)應(yīng)的數(shù)據(jù)模型中，我們可以通過操作數(shù)據(jù)模型中的數(shù)據(jù)來間接的操作數(shù)據(jù)源中的數(shù)據(jù)。

有時(shí)候，我們需要對(duì)數(shù)據(jù)模型中的數(shù)據(jù)進(jìn)行二次處理，包括數(shù)據(jù)篩選、數(shù)據(jù)排序、數(shù)據(jù)處理等等，這時(shí)候我們就得需要引入模型代理，負(fù)責(zé)對(duì)數(shù)據(jù)模型進(jìn)行處理。當(dāng)然模型代理不是必須的。QT中的模型代理有兩種都是QAbstractProxyModel的子類。分別是QIdentityProxyModel和QSortFilterProxyModel。

QIdentityProxyModel代理不會(huì)修改原有的數(shù)據(jù)模型，只是重寫了data()函數(shù)，對(duì)返回視圖的數(shù)據(jù)進(jìn)行了重新組合和修改。

QSortFilterProxyModel代理會(huì)對(duì)模型的數(shù)據(jù)進(jìn)行篩選和排序。

有了這兩個(gè)代理類，我們就可以對(duì)模型中的數(shù)據(jù)進(jìn)行處理了。

數(shù)據(jù)模型加載完畢數(shù)據(jù)之后，View層就會(huì)對(duì)數(shù)據(jù)模型中的數(shù)據(jù)進(jìn)行呈現(xiàn)了。由于數(shù)據(jù)模型中的數(shù)據(jù)都是以一個(gè)個(gè)數(shù)據(jù)單元存在的，我們可以為每個(gè)數(shù)據(jù)單元指定對(duì)應(yīng)的UI。這就用到了委托代理Delegate，委托控件可以給數(shù)據(jù)模型中的每一個(gè)元素指定固定的UI。通過委托代理的機(jī)制，我們就可以以個(gè)性的圖形界面呈現(xiàn)本地?cái)?shù)據(jù)了。

下面以一個(gè)詳細(xì)的例子，來說明一下委托代理機(jī)制的用法。例子主要功能是以縮略圖的形式對(duì)本地的圖片文件進(jìn)行管理，類似于一個(gè)圖片管理器。

本地?cái)?shù)據(jù)加載(Data)

例子中的圖片數(shù)據(jù)主要包含兩個(gè)字段，一個(gè)字段是圖片的ID，另一個(gè)字段是圖片的URL。對(duì)應(yīng)的數(shù)據(jù)結(jié)構(gòu)如下所示:

//Picture
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;   // 圖片ID
    QUrl mPictureUrl;  //圖片的地址
};

由于本地的圖片數(shù)據(jù)可能會(huì)很多，為了方便對(duì)大量的圖片數(shù)據(jù)進(jìn)行管理，這里我們采用SQLITE數(shù)據(jù)庫對(duì)圖片信息進(jìn)行本地持久化。首先，我們新建數(shù)據(jù)庫管理類，管理數(shù)據(jù)庫連接。

//DatabaseManager.h
#ifndef DATABASEMANAGER_H
#define DATABASEMANAGER_H
#include <memory>
#include <QString>
#include "PictureDao.h"
class QSqlQuery;
class QSqlDatabase;
const QString DATABASE_FILENAME = "picture.db";
class DatabaseManager
{
public:
    static void debugQuery(const QSqlQuery& query);
    //數(shù)據(jù)庫管理類是單例模式
    static DatabaseManager& instance();
    ~DatabaseManager();
protected:
    //用來構(gòu)建固定名稱的數(shù)據(jù)庫
    DatabaseManager(const QString& path = DATABASE_FILENAME);
    DatabaseManager& operator=(const DatabaseManager& rhs);
private:
    std::unique_ptr<QSqlDatabase> mDatabase;
public:
    //圖片數(shù)據(jù)操作類
    const PictureDao mpictureDao;
};
#endif // DATABASEMANAGER_H

//DatabaseManager.cpp
#include "DatabaseManager.h"
#include <QSqlDatabase>
#include <QDebug>
#include <QSqlError>
#include <QSqlQuery>
void DatabaseManager::debugQuery(const QSqlQuery& query)
{
    if (query.lastError().type() == QSqlError::ErrorType::NoError) {
        qDebug() << "Query OK:"  << query.lastQuery();
    } else {
       qWarning() << "Query KO:" << query.lastError().text();
       qWarning() << "Query text:" << query.lastQuery();
    }
}
DatabaseManager&DatabaseManager::instance()
{
    static DatabaseManager singleton;
    return singleton;
}
DatabaseManager::DatabaseManager(const QString& path) :
    mDatabase(new QSqlDatabase(QSqlDatabase::addDatabase("QSQLITE"))),
    mpictureDao(*mDatabase)
{
    mDatabase->setDatabaseName(path);
    bool openStatus = mDatabase->open();
    qDebug() << "Database connection: " << (openStatus ? "OK" : "Error");
    mpictureDao.init();
}
DatabaseManager::~DatabaseManager()
{
    mDatabase->close();
}

完成數(shù)據(jù)庫管理類的創(chuàng)建之后，我們需要添加圖片數(shù)據(jù)表的數(shù)據(jù)庫訪問對(duì)象，訪問對(duì)象負(fù)責(zé)完成對(duì)圖片數(shù)據(jù)表的增刪改查等基本操作，對(duì)應(yīng)的實(shí)現(xiàn)如下所示:

//PictureDao.h
#ifndef PICTUREDAO_H
#define PICTUREDAO_H
#include <memory>
#include <vector>
class QSqlDatabase;
class Picture;
class PictureDao
{
public:
    explicit PictureDao(QSqlDatabase& database);
    void init() const;
    //添加圖片
    void addPicture(Picture& picture) const;
    //刪除圖片
    void removePicture(int id) const;
    //加載圖片
    std::unique_ptr<std::vector<std::unique_ptr<Picture>>> loadPictures() const;
    //刪除所有的數(shù)據(jù)
    void removeAllPictures() const;
private:
    QSqlDatabase& mDatabase;
};
#endif // PICTUREDAO_H

//PictureDao.cpp
#include "PictureDao.h"
#include <QSqlDatabase>
#include <QSqlQuery>
#include <QVariant>
#include "DatabaseManager.h"
#include "picturemodel.h"
using namespace std;
PictureDao::PictureDao(QSqlDatabase& database) :
    mDatabase(database)
{
}
void PictureDao::init() const
{
    if (!mDatabase.tables().contains("pictures")) {
        QSqlQuery query(mDatabase);
        query.exec(QString("CREATE TABLE pictures")
        + " (id INTEGER PRIMARY KEY AUTOINCREMENT, "
        + "url TEXT)");
        DatabaseManager::debugQuery(query);
    }
}
void PictureDao::addPicture(Picture& picture) const
{
    QSqlQuery query(mDatabase);
    query.prepare(QString("INSERT INTO pictures")
        + " (url)"
        + " VALUES ("       
        + ":url"
        + ")");
    query.bindValue(":url", picture.pictureUrl());
    query.exec();
    DatabaseManager::debugQuery(query);
    picture.setPictureId(query.lastInsertId().toInt());
}
void PictureDao::removePicture(int id) const
{
    QSqlQuery query(mDatabase);
    query.prepare("DELETE FROM pictures WHERE id = (:id)");
    query.bindValue(":id", id);
    query.exec();
    DatabaseManager::debugQuery(query);
}
unique_ptr<vector<unique_ptr<Picture>>> PictureDao::loadPictures() const
{
    QSqlQuery query(mDatabase);
    query.prepare("SELECT * FROM pictures");
    query.exec();
    DatabaseManager::debugQuery(query);
    unique_ptr<vector<unique_ptr<Picture>>> list(new vector<unique_ptr<Picture>>());
    while(query.next()) {
        unique_ptr<Picture> picture(new Picture());
        picture->setPictureId(query.value("id").toInt());
        picture->setPictureUrl(query.value("url").toString());
        list->push_back(move(picture));
    }
    return list;
}
void PictureDao::removeAllPictures() const
{
    QSqlQuery query(mDatabase);
    query.prepare("DELETE FROM pictures WHERE 1=1");
    query.exec();
    DatabaseManager::debugQuery(query);
}

完成數(shù)據(jù)訪問層的構(gòu)建之后，我們的應(yīng)用就具備了對(duì)底層原始數(shù)據(jù)操作的能力。這個(gè)是應(yīng)用的基礎(chǔ)能力。

添加數(shù)據(jù)模型(Model)

完成了數(shù)據(jù)操作類之后，接下來我們就需要構(gòu)建對(duì)應(yīng)的數(shù)據(jù)模型了。由于圖片信息之間是沒有關(guān)聯(lián)關(guān)系的所以這里采用的是基于QAbstractListModel的列表數(shù)據(jù)模型，對(duì)應(yīng)的實(shí)現(xiàn)如下所示:

//picturemodel.h
#ifndef PICTUREMODEL_H
#define PICTUREMODEL_H
#include <memory>
#include <vector>
#include <QAbstractListModel>
#include <QUrl>
#include "DatabaseManager.h"
class PictureModel : public QAbstractListModel
{
    Q_OBJECT
public:
    //自定義每個(gè)元素的數(shù)據(jù)類型
    enum Roles {
        UrlRole = Qt::UserRole + 1,
        FilePathRole
    };
    PictureModel(QObject* parent = 0);
    //向數(shù)據(jù)模型中添加單個(gè)數(shù)據(jù)
    QModelIndex addPicture(const Picture& picture);
    Q_INVOKABLE void addPictureFromUrl(const QUrl& fileUrl);
    //模型的行數(shù)
    int rowCount(const QModelIndex& parent = QModelIndex()) const override;
    //獲取某個(gè)元素的數(shù)據(jù)
    QVariant data(const QModelIndex& index, int role) const override;
    //刪除某幾行數(shù)據(jù)
    Q_INVOKABLE bool removeRows(int row, int count, const QModelIndex& parent = QModelIndex()) override;
    //每個(gè)元素類別的名稱
    QHash<int, QByteArray> roleNames() const override;
    //加載用戶圖片
    Q_INVOKABLE void loadPictures();
    //清空模型的中的數(shù)據(jù),但不移除本地文件數(shù)據(jù)
    void clearPictures();
public slots:
    //清空模型,刪除本地文件中的數(shù)據(jù)
    void deleteAllPictures();
private:
    void resetPictures();
    bool isIndexValid(const QModelIndex& index) const;
private:
    DatabaseManager& mDatabase;
    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>>()),
    mDatabase(DatabaseManager::instance())
{
}
QModelIndex PictureModel::addPicture(const Picture& picture)
{
    int rows = rowCount();
    beginInsertRows(QModelIndex(), rows, rows);
    unique_ptr<Picture>newPicture(new Picture(picture));
    mDatabase.mpictureDao.addPicture(*newPicture);
    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) {
        //展示數(shù)據(jù)為圖片的名稱
        case Qt::DisplayRole:
            return picture.pictureUrl().fileName();
            break;
        //圖片的URL
        case Roles::UrlRole:
            return picture.pictureUrl();
            break;
        //圖片地址
        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);
        mDatabase.mpictureDao.removePicture(picture.pictureId());
    }
    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();
    mPictures = mDatabase.mpictureDao.loadPictures();
    endResetModel();
}
void PictureModel::clearPictures()
{
    resetPictures();
}
void PictureModel::resetPictures()
{   
    beginResetModel();
    mPictures.reset(new vector<unique_ptr<Picture>>());
    endResetModel();
    return;
}
void PictureModel::deleteAllPictures()
{
    mDatabase.mpictureDao.removeAllPictures();
    resetPictures();
}
bool PictureModel::isIndexValid(const QModelIndex& index) const
{
    if (index.row() < 0
            || index.row() >= rowCount()
            || !index.isValid()) {
        return false;
    }
    return true;
}

QT允許開發(fā)者針對(duì)數(shù)據(jù)模型中的每個(gè)數(shù)據(jù)單元ModelIndex定義不同的數(shù)據(jù)角色。簡單來說，就是每個(gè)數(shù)據(jù)單元可以提供各種類型的供外部使用的數(shù)據(jù)。這里我們定義了UrlRole和FilePathRole分別代表著圖片的URL和圖片的地址。

添加代理模型(Proxy)

模型代理就是對(duì)原始模型中的數(shù)據(jù)進(jìn)行二次處理，包括排序篩選等等操作。模型代理不能直接修改模型中的數(shù)據(jù)，只是負(fù)責(zé)對(duì)數(shù)據(jù)模型中的數(shù)據(jù)進(jìn)行二次處理操作。同時(shí)模型代理也不是必須的，我們也可以直接用原始的數(shù)據(jù)模型和視圖進(jìn)行交互。模型代理對(duì)應(yīng)的實(shí)現(xiàn)如下所示:

//picproxymodel.h
#ifndef PICTURE_PROXY_MODEL_H
#define PICTURE_PROXY_MODEL_H
#include <QIdentityProxyModel>
#include <QHash>
#include <QPixmap>
class PictureModel;
class PictureProxyModel : public QIdentityProxyModel
{
public:
    PictureProxyModel(QObject* parent = 0);
    //通過重寫data接口對(duì)數(shù)據(jù)進(jìn)行二次處理
    QVariant data(const QModelIndex& index, int role) const override;
    //設(shè)置獲取源數(shù)據(jù)模型
    void setSourceModel(QAbstractItemModel* sourceModel) override;
    PictureModel* pictureModel() const;
private:
    //重新加載縮略圖
    void reloadPictures();
    //生成縮略圖
    void generatePictures(const QModelIndex& startIndex, int count);
private:
   QHash<QString, QPixmap*>mPictureHashMaps;
};
#endif

//picproxymodel.cpp
#include "picproxymodel.h"
#include "PictureModel.h"
const unsigned int PICTURE_SIZE = 350;
PictureProxyModel::PictureProxyModel(QObject* parent) :
    QIdentityProxyModel(parent),
    mPictureHashMaps()
{
}
QVariant PictureProxyModel::data(const QModelIndex& index, int role) const
{
    //對(duì)原始數(shù)據(jù)模型中的數(shù)據(jù)進(jìn)行二次加工處理
    //供前端調(diào)用
    if (role != Qt::DecorationRole) {
        return QIdentityProxyModel::data(index, role);
    }
    QString filepath = sourceModel()->data(index, PictureModel::Roles::FilePathRole).toString();
    return *mPictureHashMaps[filepath];
}
void PictureProxyModel::setSourceModel(QAbstractItemModel* sourceModel)
{
    QIdentityProxyModel::setSourceModel(sourceModel);
    if (!sourceModel) {
        return;
    }
    connect(sourceModel, &QAbstractItemModel::modelReset, [this] {reloadPictures();});
    connect(sourceModel, &QAbstractItemModel::rowsInserted, [this](const QModelIndex& /*parent*/, int first, int last) {
        generatePictures(index(first, 0), last - first + 1);
    });
}
PictureModel* PictureProxyModel::pictureModel() const
{
    return static_cast<PictureModel*>(sourceModel());
}
void PictureProxyModel::reloadPictures()
{
    qDeleteAll(mPictureHashMaps);
    mPictureHashMaps.clear();
    generatePictures(index(0, 0), rowCount());
}
void PictureProxyModel::generatePictures(const QModelIndex& startIndex, int count)
{
    if (!startIndex.isValid()) {
        return;
    }
    const QAbstractItemModel* model = startIndex.model();
    int lastIndex = startIndex.row() + count;
    for(int row = startIndex.row(); row < lastIndex; row++) {
        QString filepath = model->data(model->index(row, 0), PictureModel::Roles::FilePathRole).toString();
        QPixmap pixmap(filepath);
        auto thumbnail = new QPixmap(pixmap.scaled(PICTURE_SIZE, PICTURE_SIZE,Qt::KeepAspectRatio,
                                             Qt::SmoothTransformation));
        mPictureHashMaps.insert(filepath, thumbnail);
    }
}

添加元素的代理(Delegate)

元素代理就是數(shù)據(jù)表中每個(gè)元素對(duì)應(yīng)的UI，我們通過自定義的控件來呈現(xiàn)對(duì)應(yīng)的數(shù)據(jù)。這里我們采用的是QStyledItemDelegate而不是QItemDelegate，是因?yàn)镼StyledItemDelegate支持樣式表的操作，而QItemDelegate不支持，對(duì)應(yīng)的實(shí)現(xiàn)如下所示:

//picturedelegate.h
#ifndef PICTUREDELEGATE_H
#define PICTUREDELEGATE_H
#include <QStyledItemDelegate>
#include <QMouseEvent>
class PictureDelegate : public QStyledItemDelegate
{
    Q_OBJECT
public:
    PictureDelegate(QObject* parent = 0);
    //代理的繪制事件
    void paint(QPainter* painter, const QStyleOptionViewItem& option, const QModelIndex& index) const override;
    //代理的尺寸
    QSize sizeHint(const QStyleOptionViewItem& option, const QModelIndex& index) const override;
protected:
};
#endif // PICTUREDELEGATE_H

//picturedelegate.cpp
#include "picturedelegate.h"
#include <QPainter>
//標(biāo)題欄的尺寸樣式
const unsigned int LABEL_HEIGHT = 20;
const unsigned int LABEL_COLOR = 0x303030;
const unsigned int LABEL_ALPHA = 200;
const unsigned int LABEL_TEXT_COLOR = 0xffffff;
const unsigned int HIGHLIGHT_ALPHA = 100;
//圖片的尺寸樣式
const unsigned int PIXMAP_WIDTH = 200;
const unsigned int PIXMAP_HEIGHT = 200;
PictureDelegate::PictureDelegate(QObject* parent) :
    QStyledItemDelegate(parent)
{
}
void PictureDelegate::paint(QPainter* painter, const QStyleOptionViewItem& option, const QModelIndex& index) const
{
    painter->save();
    //繪制對(duì)應(yīng)的圖片
    QPixmap pixmap = index.model()->data(index, Qt::DecorationRole).value<QPixmap>();
    painter->drawPixmap(option.rect.x(), option.rect.y(),PIXMAP_WIDTH,PIXMAP_HEIGHT,pixmap);
    //繪制圖片的標(biāo)題欄顯示圖片名稱
    QRect bannerRect = QRect(option.rect.x(), option.rect.y(), PIXMAP_WIDTH, LABEL_HEIGHT);
    QColor bannerColor = QColor(LABEL_COLOR);
    bannerColor.setAlpha(LABEL_ALPHA);
    painter->fillRect(bannerRect, bannerColor);
    //繪制標(biāo)題文字
    QString filename = index.model()->data(index, Qt::DisplayRole).toString();
    painter->setPen(LABEL_TEXT_COLOR);
    painter->drawText(bannerRect, Qt::AlignCenter, filename);
    //設(shè)置元素被選中之后的顏色
    if (option.state.testFlag(QStyle::State_Selected)) {
        QColor selectedColor = option.palette.highlight().color();
        selectedColor.setAlpha(HIGHLIGHT_ALPHA);
        painter->fillRect(option.rect, selectedColor);
    }
    painter->restore();
}
QSize PictureDelegate::sizeHint(const QStyleOptionViewItem& /*option*/, const QModelIndex& index) const
{
    const QPixmap& pixmap = index.model()->data(index, Qt::DecorationRole).value<QPixmap>();
    return QSize(PIXMAP_WIDTH,PIXMAP_HEIGHT);
}

我們也可以通過實(shí)現(xiàn)QStyledItemDelegate::createEditor()接口，來對(duì)每一個(gè)元素代理中的數(shù)據(jù)進(jìn)行編輯，這里就不詳細(xì)介紹了，之前的文章中寫過。

添加視圖層(View)

完善了數(shù)據(jù)模型和元素代理之后，對(duì)應(yīng)的視圖層操作就比較簡單了。視圖層我們添加了和用戶交互的接口，用戶可以通過對(duì)應(yīng)的UI操作，對(duì)數(shù)據(jù)模型中的數(shù)據(jù)進(jìn)行增刪改查。同時(shí)視圖中我們?yōu)樵靥砑恿瞬藛?，我們可以通過右鍵菜單來刪除某個(gè)特定的元素。

//mylistview.h
#ifndef MYLISTVIEW_H
#define MYLISTVIEW_H
#include <QWidget>
#include <QItemSelectionModel>
#include <QMouseEvent>
#include <QMenu>
namespace Ui {
class MyListView;
}
class PictureProxyModel;
class MyListView : public QWidget
{
    Q_OBJECT
public:
    explicit MyListView(QWidget *parent = 0);
    ~MyListView();
    //設(shè)置數(shù)據(jù)模型
    void setPictureModel(PictureProxyModel *pictureModel);
    //設(shè)置選中的數(shù)據(jù)模型
    void setPictureSelectionModel(QItemSelectionModel *selectionModel);
private slots:
    void addPictures();
    void delPictures();
    void clearPictures();
    void delAllPicture();
    void delCurrentPicture();
    void showCustomMenu(const QPoint& pos);
private:
    Ui::MyListView *ui;
    //圖片數(shù)據(jù)模型
    PictureProxyModel* mPictureModel;
    //選中元素的數(shù)據(jù)模型
    QItemSelectionModel* mPictureSelectionModel;
    QModelIndex mCurrentIndex;
    QMenu* m_func_menu = nullptr;
    QAction* m_del_current_pic = nullptr;
};
#endif // MYLISTVIEW_H

//mylistview.cpp
#pragma execution_character_set("utf-8")
#include "mylistview.h"
#include "picturedelegate.h"
#include "picproxymodel.h"
#include "ui_mylistview.h"
#include "picturemodel.h"
#include <QFileDialog>
#include <QInputDialog>
#include <QStandardPaths>
MyListView::MyListView(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::MyListView)
{
    ui->setupUi(this);
    //設(shè)置元素之間的間隔
    ui->pic_list_view->setSpacing(5);
    //設(shè)置尺寸變化策略
    ui->pic_list_view->setResizeMode(QListView::Adjust);
    //設(shè)置元素增減的時(shí)候的變化模式
    ui->pic_list_view->setFlow(QListView::LeftToRight);
    //設(shè)置伸縮的時(shí)候是否自動(dòng)換行
    ui->pic_list_view->setWrapping(true);
    //設(shè)置每個(gè)元素的代理
    ui->pic_list_view->setItemDelegate(new PictureDelegate(this));
    //開啟自定義的菜單
    ui->pic_list_view->setContextMenuPolicy(Qt::CustomContextMenu);
    //初始化功能菜單
    m_func_menu = new QMenu(this);
    m_del_current_pic = new QAction("刪除當(dāng)前圖片",this);
    m_func_menu->addAction(m_del_current_pic);
    connect(m_del_current_pic,&QAction::triggered,this,&MyListView::delCurrentPicture);
    //對(duì)圖片數(shù)據(jù)進(jìn)行增刪改查
    connect(ui->add_pic_btn, &QPushButton::clicked, this, &MyListView::addPictures);
    connect(ui->clear_btn, &QPushButton::clicked,this, &MyListView::clearPictures);
    connect(ui->del_pic_btn, &QPushButton::clicked, this, &MyListView::delPictures);
    connect(ui->del_all_pic_btn,&QPushButton::clicked,this,&MyListView::delAllPicture);
    connect(ui->pic_list_view,&QListView::customContextMenuRequested,this,&MyListView::showCustomMenu);
}
MyListView::~MyListView()
{
    delete ui;
}
void MyListView::setPictureModel(PictureProxyModel* pictureModel)
{
    mPictureModel = pictureModel;
    ui->pic_list_view->setModel(pictureModel);
}
void MyListView::setPictureSelectionModel(QItemSelectionModel* selectionModel)
{
    mPictureSelectionModel = selectionModel;
    ui->pic_list_view->setSelectionModel(selectionModel);
}
void MyListView::addPictures()
{
    QStringList filenames = QFileDialog::getOpenFileNames(this,
                                                          "添加圖片",
                                                          QStandardPaths::writableLocation(QStandardPaths::DesktopLocation),
                                                          "Picture files (*.jpg *.png)");
    if (!filenames.isEmpty()) {
        QModelIndex lastModelIndex;
        for (auto filename : filenames) {
            Picture picture(filename);
            lastModelIndex = mPictureModel->pictureModel()->addPicture(picture);
            lastModelIndex = mPictureModel->index(lastModelIndex.row(),lastModelIndex.column());
        }
        if(lastModelIndex.isValid())
        {
            ui->pic_list_view->setCurrentIndex(lastModelIndex);
        }
    }
}
void MyListView::delPictures()
{
    if (mPictureSelectionModel->selectedIndexes().isEmpty()) {
        return;
    }
    int row = mPictureSelectionModel->currentIndex().row();
    mPictureModel->sourceModel()->removeRow(row);
    //選中前一個(gè)圖片
    QModelIndex previousModelIndex = mPictureModel->sourceModel()->index(row - 1, 0);
    if(previousModelIndex.isValid()) {
        previousModelIndex = mPictureModel->index(previousModelIndex.row(),previousModelIndex.column());
        mPictureSelectionModel->setCurrentIndex(previousModelIndex, QItemSelectionModel::SelectCurrent);
        return;
    }
    //選中后一個(gè)圖片
    QModelIndex nextModelIndex = mPictureModel->sourceModel()->index(row, 0);
    if(nextModelIndex.isValid()) {
        nextModelIndex = mPictureModel->index(nextModelIndex.row(),nextModelIndex.column());
        mPictureSelectionModel->setCurrentIndex(nextModelIndex, QItemSelectionModel::SelectCurrent);
        return;
    }
}
void MyListView::clearPictures()
{
    PictureModel* pic_model = (PictureModel*)mPictureModel->sourceModel();
    pic_model->clearPictures();
}
void MyListView::delAllPicture()
{
    PictureModel* pic_model = (PictureModel*)mPictureModel->sourceModel();
    pic_model->deleteAllPictures();
}
void MyListView::delCurrentPicture()
{
    if(mCurrentIndex.isValid())
    {
        PictureModel* pic_model = (PictureModel*)mPictureModel->sourceModel();
        pic_model->removeRow(mCurrentIndex.row());
    }
}
void MyListView::showCustomMenu(const QPoint &pos)
{
    QPoint point = pos;
    mCurrentIndex = ui->pic_list_view->indexAt(pos);
    if(mCurrentIndex.isValid() && mCurrentIndex.row() >= 0)
    {
        m_func_menu->exec(ui->pic_list_view->mapToGlobal(point));
    }
}

完善了列表視圖之后，我們就可以在主界面中，添加視圖控件了，這也是UI層的最后一步操作了，對(duì)應(yīng)的實(shí)現(xiàn)如下:

//mainwwindow.h
#ifndef MAINWWINDOW_H
#define MAINWWINDOW_H
#include <QWidget>
#include "mylistview.h"
namespace Ui {
class MainwWindow;
}
class MainwWindow : public QWidget
{
    Q_OBJECT
public:
    explicit MainwWindow(QWidget *parent = 0);
    ~MainwWindow();
private:
    MyListView* mListView=nullptr;
};
#endif // MAINWWINDOW_H

//mainwwindow.cpp
#include "mainwwindow.h"
#include "ui_mainwwindow.h"
#include "picturemodel.h"
#include "picproxymodel.h"
#include <QHBoxLayout>
MainwWindow::MainwWindow(QWidget *parent) :
    QWidget(parent)
{
    mListView = new MyListView(this);
    PictureModel* pic_model = new PictureModel(this);
    PictureProxyModel* pic_proxy_model = new PictureProxyModel(this);
    pic_proxy_model->setSourceModel(pic_model);
    QItemSelectionModel* pictureSelectionModel = new QItemSelectionModel(pic_proxy_model, this);
    mListView->setPictureModel(pic_proxy_model);
    mListView->setPictureSelectionModel(pictureSelectionModel);
    pic_model->loadPictures();
    QHBoxLayout* main_layout = new QHBoxLayout(this);
    main_layout->addWidget(mListView);
    this->setLayout(main_layout);
    this->setFixedSize(910,600);
}
MainwWindow::~MainwWindow()
{
}

使用效果

到此這篇關(guān)于QT委托代理機(jī)制之Model View Delegate使用方法詳解的文章就介紹到這了,更多相關(guān)QT Model View Delegate內(nèi)容請(qǐng)搜索腳本之家以前的文章或繼續(xù)瀏覽下面的相關(guān)文章希望大家以后多多支持腳本之家！

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