Qt添加事件过滤器，设置拖放listWidget、TreeWidget、TableWidget控件。

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);



    //设置控件可以拖放
    ui->listWidgetSourse->setAcceptDrops(true);
    ui->listWidgetSourse->setDragEnabled(true);
    ui->listWidgetSourse->setDefaultDropAction(Qt::CopyAction);
    ui->listWidgetSourse->setDragDropMode(QAbstractItemView::DragDrop);

    ui->listWidget->setAcceptDrops(true);
    ui->listWidget->setDragEnabled(true);
    ui->listWidget->setDefaultDropAction(Qt::CopyAction);
    ui->listWidget->setDragDropMode(QAbstractItemView::DragDrop);

    ui->treeWidget->setAcceptDrops(true);
    ui->treeWidget->setDragEnabled(true);
    ui->treeWidget->setDefaultDropAction(Qt::CopyAction);
    ui->treeWidget->setDragDropMode(QAbstractItemView::DragDrop);

    ui->tableWidget->setAcceptDrops(true);
    ui->tableWidget->setDragEnabled(true);
    ui->tableWidget->setDefaultDropAction(Qt::MoveAction);
    ui->tableWidget->setDragDropMode(QAbstractItemView::DragDrop);

    //为小部件添加事件过滤器
    ui->listWidgetSourse->installEventFilter(this);
    ui->listWidget->installEventFilter(this);
    ui->treeWidget->installEventFilter(this);
    ui->tableWidget->installEventFilter(this);
}

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

void MainWindow::refreshToUI(QGroupBox *currGroupBox)
{
    ui->checkBoxAcceptDrops->setChecked(m_itemView->acceptDrops());
    ui->checkBoxDropEnabled->setChecked(m_itemView->dragEnabled());

    ui->comboBox->setCurrentIndex((int)m_itemView->dragDropMode());
    int index = getGroupActionIndex(m_itemView->defaultDropAction());
    ui->comboBoxDefaultAction->setCurrentIndex(index);

    QFont fout = ui->groupBoxSourse->font();
    fout.setBold(false);
    ui->groupBox->setFont(fout);
    ui->groupBoxList->setFont(fout);
    ui->groupBoxSourse->setFont(fout);
    ui->groupBoxTree->setFont(fout);

    fout.setBold(true);
    currGroupBox->setFont(fout);
}

int MainWindow::getGroupActionIndex(Qt::DropAction actionType)
{
    switch (actionType) {
        case Qt::CopyAction :
            return 0;
        case Qt::MoveAction :
            return 1;
        case Qt::LinkAction :
            return 2;
        case Qt::ActionMask :
            return 3;
        default:
            return 0;
    }
}

Qt::DropAction MainWindow::getGroupActionTyp(int index)
{
    switch (index) {
        case 0:
            return Qt::CopyAction;
        case 1:
            return Qt::MoveAction;
        case 2:
            return Qt::LinkAction;
        case 3:
            return Qt::ActionMask;
        default:
            return Qt::CopyAction;
    }
}


//设置返回值，如果将返回值设置为eventFilter(watched,event);，程序直接奔溃，目前还没有找到原因
bool MainWindow::eventFilter(QObject *watched, QEvent *event)
{
    if(event->type() != QEvent::KeyPress){
        return  false;
        // return  eventFilter(watched,event);
    }
    QKeyEvent * keyEvent = static_cast<QKeyEvent*>(event);
    if(keyEvent->key() != Qt::Key_Delete){
         return  false;
      // return   eventFilter(watched,event);
    }

    if(watched == ui->listWidgetSourse){//判断是否是listWidgetSourse委托
        delete ui->listWidgetSourse->takeItem(ui->listWidgetSourse->currentRow());//删除当前行
    }else if(watched == ui->listWidget){
        delete ui->listWidget->takeItem(ui->listWidget->currentRow());//删除当前行
    }else if(watched == ui->treeWidget){
        QTreeWidgetItem * treeItem = ui->treeWidget->currentItem();//获取当前索引项。tree中需要判断这个tree到底有没有父项
        if(treeItem->parent() != nullptr){//判断父索引是否为空
            treeItem->parent()->removeChild(treeItem);
        }else{
            int index = ui->treeWidget->indexOfTopLevelItem(treeItem);
            ui->treeWidget->takeTopLevelItem(index);
        }
        delete treeItem;
    }else if(watched == ui->tableWidget){
        delete ui->tableWidget->takeItem(ui->tableWidget->currentRow(),ui->tableWidget->currentColumn());
    }

    return  eventFilter(watched,event);
     //return true;
}


void MainWindow::on_radioButton_clicked()
{
    m_itemView = ui->listWidgetSourse;
    refreshToUI(ui->groupBoxSourse);
}

void MainWindow::on_radioButtonList_clicked()
{
    m_itemView = ui->listWidget;
    refreshToUI(ui->groupBoxList);
}

void MainWindow::on_radioButtonTree_clicked()
{
    m_itemView = ui->treeWidget;
    refreshToUI(ui->groupBoxTree);
}

void MainWindow::on_radioButtonTable_clicked()
{
    m_itemView = ui->tableWidget;
    refreshToUI(ui->groupBox);
}