QFlags tutorial
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Overview
First of all we should write about the macro:
Q_FLAGS
This macro registers one or several flags types to the meta-object system
Example:
class TestClass
{
public:
enum Option {
OptionA = 1, // 000001
OptionB = 2, // 000010
OptionC = 4, // 000100
OptionD = 8, // 001000
OptionE = 16, // 010000
OptionF = 32 // 100000
// … some more options with value which is a power of two
};
Q_DECLARE_FLAGS(Options, Option)
};
Q_DECLARE_OPERATORS_FOR_FLAGS(TestClass::Options)
The Q_DECLARE_FLAGS() macro expands to typedef QFlags<Enum> Flags; In our case it expandes to typedef QFlags<Option> Options; where Option - is an enum name, and Options - is name for set of flags.
The Q_DECLARE_OPERATORS_FOR_FLAGS() macro declares global operator|() functions for Flags, which is of type QFlags<T>.
The Q_DECLARE_FLAGS() macro does not expose the flags to the meta-object system, so they cannot be used by Qt Script. To make the flags available for these purpose, the Q_FLAGS() macro must be used.
Usage sample
void test (TestClass::Options flag)
{
if (flag.testFlag(TestClass::OptionA))
qDebug() << "A";
if (flag.testFlag(TestClass::OptionB))
qDebug() << "B";
}
int main()
{
test (TestClass::OptionA | TestClass::OptionB);
test (0x1); // error
}
The testFlag(flag) method checks if flag is set in QFlags.
Some examples
TestClass::Options f1(TestClass::OptionA | TestClass::OptionB); // 000011
TestClass::Options f2(~f1); // 111100
TestClass::Options f3(Foo::OptionA | Foo::OptionC); // 000101
TestClass::Options f4(f1^f3); // 000110