c++ - qInstallMessageHandler 不接受公共(public)方法作为参数

Question

我正在使用 Qt 5.7 开发一个项目LtLogger 类有问题:

#ifndef LTLOGGER_H
#define LTLOGGER_H

#include <QObject>
#include <QScopedPointer>
#include <QFile>
#include <QMutexLocker>
#include <QDateTime>
#include <QThread>
#include <QMutex>
#include <QApplication>

#include <utils/config.h>
#include "ltlogsocket.h"

/**
 * @brief Log backup folder name
 */
static const QString LT_LOG_BACKUP_FOLDER_NAME="logBackup";
#ifdef PLATFORM_NEXO360
/**
 * @brief Log file name
 */
static const QString LT_LOG_FILE_NAME="dc.log";
#endif

/**
 * @class Logger class
 */
class LtLogger : public QObject
{
    Q_OBJECT

public:
    /**
     * @brief Constructor
     * @param parent
     */
    explicit LtLogger(QObject* const parent,
                      Config* const ltConfig);

    /**
     * @brief Message handler method
     * @param type
     * @param ctx
     * @param msg
     */
    void ltMessageHandler(QtMsgType type,
                          const QMessageLogContext& ctx,
                          const QString& msg);

signals:

public slots:
};

#endif // LTLOGGER_H

及其实现:

#include "ltlogger.h"

LtLogger::LtLogger(QObject *parent,
                   Config* const ltConfig)
    : QObject(parent),
      m_ltLogSocket(new LtLogSocket(parent,
                                    ltConfig))
{
    qInstallMessageHandler(ltMessageHandler);
}   // constructor

void LtLogger::ltMessageHandler(QtMsgType type,
                                const QMessageLogContext& ctx,
                                const QString& msg)
{
    QString func = ctx.function;
    func = func.left(func.lastIndexOf("("));
    func = func.mid(func.indexOf(" "));
    func = func.mid(func.indexOf("::")+2);

    QString currTime = QDateTime::currentDateTime().toString("yyyy-MM-dd HH:mm:ss.zzz");

    QString txt;
    switch (type) {
    case QtInfoMsg:
        txt = QString("%1 [%2] %3/%4: %5").arg(currTime).arg(QThread::currentThread()->objectName()).arg("I").arg(func).arg(msg);
        break;
    case QtDebugMsg:
        txt = QString("%1 [%2] %3/%4: %5").arg(currTime).arg(QThread::currentThread()->objectName()).arg("D").arg(func).arg(msg);
        break;
    case QtWarningMsg:
        txt = QString("%1 %2/%3: %4").arg(currTime).arg("W").arg(func).arg(msg);
    break;
    case QtCriticalMsg:
        txt = QString("%1 %2/%3 (%4.%5): %6").arg(currTime).arg("C").arg(func).arg(ctx.file).arg(ctx.line).arg(msg);
    break;
    case QtFatalMsg:
        txt = QString("%1 %2/%3 (%4.%5): %6").arg(currTime).arg("F").arg(func).arg(ctx.file).arg(ctx.line).arg(msg);
        abort();
    }

    QTextStream ts(m_ltLogFile.data());

    ts << txt << endl;
    ts.flush();    // Clear the buffered data

    ltCleanupLogs();
}   // ltMessageHandler

当我尝试构建项目时，出现以下错误:

ltlogger.cpp: In constructor ‘LtLogger::LtLogger(QObject*, Config*)’:
ltlogger.cpp:9:44: error: invalid use of non-static member function ‘void LtLogger::ltMessageHandler(QtMsgType, const QMessageLogContext&, const QString&)’
     qInstallMessageHandler(ltMessageHandler);

我错过了什么，如何将成员方法注册为消息处理程序，我在构造函数中尝试过，正如您从代码中看到的那样。

Answer 1

编译器给出了正确的提示。 QtMessageHandler 是一个独立的函数:

typedef void (*QtMessageHandler)(QtMsgType, const QMessageLogContext &, const QString &);

您可以像这样使用您的处理程序:

LtLogger globalLogger;

void messageHandler(QtMsgType type, const QMessageLogContext& ctx, const QString& msg){
       globalLogger.ltMessageHandler(type, ctx, msg);
}

[...]
qInstallMessageHandler(messageHandler);