Qt运行报错QWidget: Must construct a QApplication before a QWidget

报错文件为widget.cpp,原代码如下：

#include <memory>
    QLineEdit   *frequency = new QLineEdit();
    QComboBox   *cbBox_method = new QComboBox();
    QLineEdit   *X_MAXvalue = new QLineEdit();
    QLineEdit   *Y_MAXvalue = new QLineEdit();
    QLineEdit   *X_MINvalue = new QLineEdit();
    QLineEdit   *Y_MINvalue = new QLineEdit();
    QLineEdit   *X_average = new QLineEdit();
    QLineEdit   *Y_average = new QLineEdit();
    char fileName[256];
    FILE *fp=NULL;
    int k;
    unsigned short fileBuf[1024];
    int32 bFileHeaderSize=0;
    int32 byteSize=0;
    int32 historyFileLen=0;
    double voltData[1024];
    int32 pointsFetched=0;
    int32 chunksFetched=0;
    std::deque<double>datadeque;
    double voltage;
    int buff_busy=0;
Widget::Widget(QWidget *parent): QWidget(parent), ui(new Ui::Widget)
{
    ui->setupUi(this);
}

问题在于，QObject变量是基于UI的变量，不能在Widget出现之前定义，应该定义在Widget之后