QT信槽编程，QObject::connect: Cannot connect (null)报错的两种成因

来源：互联网发布：nba体测数据查询编辑：程序博客网时间：2024/05/22 13:26

{connect(ui.btnHelp, SIGNAL(clicked()), this, SLOT(OnBtnHelp()));connect(ui.btnHelp, SIGNAL(toggled(bool)), this, SLOT(OnBtnHelpChanged(bool)));ui.setupUi(this);}

上面这段代码报错如下:

QObject::connect: Cannot connect (null)::clicked() to Test5_4::OnBtnHelp()QObject::connect: Cannot connect (null)::toggled(bool) to Test5_4::OnBtnHelpChanged(bool)

这是ui没有被提前初始化的原因，把最后一段代码前置就可以了，原因是：（quote自http://blog.csdn.net/oowgsoo/article/details/1529411#comments）

即编译器未能识别到信号发送者，sender为零时，报错NULL。

 // 不允许空输入    if (sender == 0 || receiver == 0 || signal == 0 || method == 0) {#ifndef QT_NO_DEBUG        qWarning("Object::connect: Cannot connect %s::%s to %s::%s",                 sender ? sender->metaObject()->className() : "(null)",                 signal ? signal+1 : "(null)",                 receiver ? receiver->metaObject()->className() : "(null)",                 method ? method+1 : "(null)");#endif        return false;    }

发送和接收者定义重叠，也会保类似错误，详见：

http://stackoverflow.com/questions/8493506/qobjectconnect-cannot-connect-null

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