Step 2-bit shift enumeration

Displacement enumeration

• Displacement enumeration is a very old C-language technique
• Bitwise AND if all is 1 the result is 1
• Bitwise OR if all is 0 the result is 0

Drill

1 Defining enumeration types

Action Type Enumeration

typedef enum {

Actiontypetop = 1 << 0,

Actiontypebottom = 1 << 1,

Actiontypeleft = 1 << 2,

Actiontyperight = 1 << 3

} ActionType;

• Method Target

Respond differently depending on the type of operation parameter

The type of operation can be any combination

• Method implementation

-(void) Action: (ActionType) Type {

if (type = = 0) {

NSLog (@ "no operation");

Return

}

if (type & actiontypetop) {

NSLog (@ "Top%tu", type & Actiontypetop);

}

if (type & Actiontypebottom) {

NSLog (@ "Bottom%tu", type & Actiontypebottom);

}

if (type & Actiontypeleft) {

NSLog (@ "left%tu", type & Actiontypeleft);

}

if (type & actiontyperight) {

NSLog (@ "Right%tu", type & Actiontyperight);

}

}

• Method invocation

ActionType type = Actiontypetop | Actiontyperight;

[Self action:type];

Code Summary

• Use a bitwise or can set multiple types for one parameter at the same time
• Use bitwise and can determine the specific type when executing
• With the displacement setting, you can get a lot of combinations!
• For a displacement enumeration type, if 0 is passed in, it means that no additional operations are done, and the execution efficiency is usually the highest
• If in development, see the enumeration of displacements, and do not do any additional operations, parameters can be directly input 0!

IOS Unique Syntax

• After IOS 5.0, provides a new way to define enumerations
• Specifies the type of data in the enumeration, while defining the enumeration
• typedef ns_options (Nsuinteger, nsjsonreadingoptions)

Displacement enumeration, you can use a bitwise OR SET value

• typedef ns_enum (Nsinteger, Uitableviewstyle)

Numeric enumeration, setting values directly using enumerations

typedef ns_options (Nsuinteger, ActionType) {

Actiontypetop = 1 << 0,

Actiontypebottom = 1 << 1,

Actiontypeleft = 1 << 2,

Actiontyperight = 1 << 3

};

Step 2-bit shift enumeration