Qt實現截圖選擇框（僅實現選擇框創建，非完整的截圖功能）併發射信號給調用的槽函數

頭文件：

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include "mywidget.h"

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

private:
    Ui::MainWindow *ui;
private slots:
    void OnSelectedBtn(QRect a);
};

#endif // MAINWINDOW_H

mywidget.h（繼承於QWidget）

#ifndef MYWIDGET_H
#define MYWIDGET_H

#include <QWidget>
#include <QPixmap>
#include <QPainter>
#include <QPaintEvent>
#include <QMouseEvent>
#include <QPoint>

class MyWidget : public QWidget
{
    Q_OBJECT
public:
    explicit MyWidget(QWidget *parent = 0);

signals:
    void selected(QRect a);//信號
public slots:

private:
    void paintEvent(QPaintEvent *event);        //繪圖函數
    void mouseMoveEvent(QMouseEvent *event);    //鼠標移動
    void mousePressEvent(QMouseEvent *event);   //鼠標點擊
    void mouseReleaseEvent(QMouseEvent *event); //鼠標擡起
private:
    QPixmap my_picture;
    bool m_pressedFlag;//獲取鼠標是否按下
    QPoint currPos;//鼠標當前位置
    QPoint startPos,endPos;//起始、結束、座標
};

#endif // MYWIDGET_H

源文件：

main.cpp

#include "mainwindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

//    MyWidget p;
//    p.resize(400,300);
//    p.move(200,200);
//    p.show();

    return a.exec();
}

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QDebug>

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    connect(ui->selectedwidget,SIGNAL(selected(QRect)),
            this,SLOT(OnSelectedBtn(QRect)));
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::OnSelectedBtn(QRect a)
{
    qDebug() << "關聯......";
}

mywidget.cpp

#include "mywidget.h"
#include <QtGui>

MyWidget::MyWidget(QWidget *parent) :
    QWidget(parent)
{
    m_pressedFlag = false;
    startPos = endPos = QPoint(0,0);
    my_picture.load("D:/QT_Library/QJie_Tu/1.jpg");//圖片存放位置
}

void MyWidget::paintEvent(QPaintEvent *event)//繪圖函數
{
    QPainter painter(this);

    int width = this->width();
    int height = this->height();

    painter.drawPixmap(0,0,width,height,my_picture);//添加本地圖片作爲背景
    if(m_pressedFlag)//如果鼠標按下
    {
        //構建十字交叉線
        painter.setPen(QColor(0xFF,0,0));//設置線條顏色
        painter.drawLine(QPoint(0,currPos.y()),QPoint(width,currPos.y()));//X軸
        painter.drawLine(QPoint(currPos.x(),0),QPoint(currPos.x(),height));//Y軸
    }
    QRect select(startPos,endPos);//構建截圖選擇框
    //普通畫法
//    painter.setBrush(QColor(0x88,0x88,0x88));
//    painter.drawRect(select);
    //透明度畫法
    QRect full(0,0,width,height);
    painter.setBrush(QColor(0,0,0,100));
    painter.setClipRegion(QRegion(full)-QRegion(select));
    painter.drawRect(full);
}

void MyWidget::mouseMoveEvent(QMouseEvent *event)//鼠標移動
{
    if(m_pressedFlag)
    {
        currPos = event->pos();
        endPos = event->pos();
        update();
    }
}

void MyWidget::mousePressEvent(QMouseEvent *event)//鼠標按下
{
    m_pressedFlag = true;
    startPos = endPos = event->pos();//截圖框開始座標
}

void MyWidget::mouseReleaseEvent(QMouseEvent *event)//鼠標擡起
{
    m_pressedFlag = false;
    update();
    QRect a(startPos,endPos);
    emit selected(a);//發射信號
}

設計界面：（選擇Widget控件，提升爲自定義控件）

效果圖：