QVariant::isNull() method (Qt 5.2)
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The documentation says:
"Returns true if this is a null variant, false otherwise. A variant is considered null if it contains a default constructed value or a built-in type instance that has an isNull method, in which case the result would be the same as calling isNull on the wrapped object."This seems not correct to me. When creating a QVariant by "QVariant boolVariant = bool();" "boolVariant.isNull()" returns false. However according to the above description is should return true since it contains a default constructed value.
Is the documentation misleading? How should it read? How does isNull() actually work?
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Hi,
You are mistaken with C and C++ IYAM.
What you do, is create a QVariant with a default constructor and reassign the value to hold the value created via a default constructed bool. So the QVariant hold a VALUE, not a DEFAULT VALUE, thus returns false!
You should test:
@
QVariant boolVariant (bool());
// or
QVariant boolVariant;
// NOT: THIS IS C code, NOT C++
QVariant boolVariant = bool();
@
This IS a default constructed QVariant! -
"QVariant boolVariant = bool();" definitely calls the "QVariant::QVariant(bool)" constructor directly in C++. I used the debugger to verify this.
Also line 3 of your example contructs an invalid variant (which is not the same as a null variant).
It seems the only way to create a null-variant is something like "QVariant(QVariant::Int)" or by wrapping an object that has its own isNull() method. Still I have no idea why the documentation mentions default constructed values.
