QFlags and enum 用法

随手一翻，翻到一篇简易教程，用于安全使用QFlags


http://qt-project.org/wiki/QFlags_tutorial

Simple tutorial for safe-usage QFlags



Overview


First of all we should write about macro Q_FLAGSThis macro registers one or several flags types to the meta-object system[font=Verdana, 'DejaVu Sans', Geneva, sans-serif]

Example:

1. 
   class TestClass
2. 
   {
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   public:
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        enum Option {
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            OptionA = 0x0,  // 0x000000
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            OptionB = 0x1,  // 0x000001
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            OptionC = 0x2,  // 0x000010
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            OptionD = 0x4,  // 0x000100
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            OptionE = 0x8,  // 0x001000
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             OptionF = 0x16 // 0x010000
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             // ... some more options with value which is a power of two
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         };
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         Q_DECLARE_FLAGS(Options, Option)
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    };
15. 
    
16. 
    Q_DECLARE_OPERATORS_FOR_FLAGS(TestClass::Options)

The Q_DECLARE_FLAGS() macro expands to

1. 
   typedef QFlags<Enum> Flags;

[font=Verdana, 'DejaVu Sans', Geneva, sans-serif]In our case it expandes to typedef QFlags<Option> Options;[font=Verdana, 'DejaVu Sans', Geneva, sans-serif] where Option[font=Verdana, 'DejaVu Sans', Geneva, sans-serif] – is an enum name, and Options[font=Verdana, 'DejaVu Sans', Geneva, sans-serif] – 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.[font=Verdana, 'DejaVu Sans', Geneva, sans-serif]

Usage sample

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   void test (TestClass::Options flag)
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   {
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     if (flag.testFlag(TestClass::OptionA))
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       qDebug() << "A";
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     if (flag.testFlag(TestClass::OptionB))
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       qDebug() << "B";
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   }
8. 
   
9. 
   int main()
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    {
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      test (TestClass::OptionA | TestClass::OptionB);
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      test (0x1);  // error
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    }

testFlag(flag) method checks if flag is set in QFlags.[font=Verdana, 'DejaVu Sans', Geneva, sans-serif]

Some example

1. 
   TestClass::Options f1(TestClass::OptionA | TestClass::OptionB);   // 000011
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   TestClass::Options f2(~f1);                                       // 111100
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   TestClass::Options f3(Foo::OptionA | Foo::OptionC);               // 000101
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   TestClass::Options f4(f1^f3);                                     // 000110