TypeError: setHorizontalHeader(self, header: QHeaderView): argument 1 has unexpected type 'QWidget'

抱歉，上面的代码有误。setHorizontalHeader()方法的参数应该是一个QHeaderView对象，而不是QWidget对象。下面是修改后的代码：

from PyQt5.QtWidgets import QApplication, QMainWindow, QWidget, QTableWidget, QHeaderView, QComboBox, QVBoxLayout, QTableWidgetItem
from PyQt5.QtCore import Qt

class MainWindow(QMainWindow):
    def __init__(self):
        super().__init__()
        self.table = QTableWidget()
        self.table.setColumnCount(2)
        self.table.setRowCount(3)
        self.table.setHorizontalHeaderLabels(['Name', 'Age'])

        for i in range(3):
            name_item = QTableWidgetItem(f'name_{i}')
            age_item = QTableWidgetItem(f'{i*10}')
            self.table.setItem(i, 0, name_item)
            self.table.setItem(i, 1, age_item)

        self.setCentralWidget(self.table)

        # 添加下拉多选框
        combo_box = QComboBox(self)
        combo_box.addItems(['Select All', 'Unselect All'])
        combo_box.currentIndexChanged.connect(self.on_combo_box_change)
        
        # 将下拉多选框添加到表头
        header_v_box = QVBoxLayout()
        header_v_box.addWidget(self.table.horizontalHeader())
        header_v_box.addWidget(combo_box)
        header_v_box.setContentsMargins(0, 0, 0, 0)

        header_widget = QWidget()
        header_widget.setLayout(header_v_box)

        self.table.setHorizontalHeader(header_widget.header())

    def on_combo_box_change(self, index):
        if index == 0:  # 选择全部
            for i in range(self.table.rowCount()):
                item = self.table.item(i, 0)
                item.setCheckState(Qt.Checked)
        elif index == 1:  # 取消选择
            for i in range(self.table.rowCount()):
                item = self.table.item(i, 0)
                item.setCheckState(Qt.Unchecked)

if __name__ == '__main__':
    app = QApplication([])
    window = MainWindow()
    window.show()
    app.exec_()

这段代码中，我们将QWidget对象转换为QHeaderView对象，使用header()方法实现。这样就可以正确设置表格的水平表头了。