App States with BOOL flags

问题

I've got 5 states in my app, and I use BOOL flags to mark them. But it isn't straightforward, because I have to write 5 lines to change all flags when I want to change state.

Can you write some ideas or simple code to solve this problem?

code:

//need to choose second state
flag1 = false;
flag2 = true;
flag3 = false;
flag4 = false;
flag5 = false;

Also, it's to bad because I can choose 2 states one time.

P.S. I found modern and more Apple-way. Answer below.

回答1:

Use typedef enum to define all possible states using bitmasks.

Note this will give you a maximum of up to 64 different states (on most platforms). If you need more possible states, this solution will not work.

Handling this scheme will require you to fully understand and safely handle boolean algebra.

//define all possible states
typedef enum
{
    stateOne = 1 << 0,     // = 1
    stateTwo = 1 << 1,     // = 2
    stateThree = 1 << 2,   // = 4
    stateFour = 1 << 3,    // = 8  
    stateFive = 1 << 4     // = 16
} FiveStateMask;

//declare a state
FiveStateMask state;

//select single state
state = stateOne;         // = 1

//select a mixture of two states
state = stateTwo | stateFive;     // 16 | 2 = 18

//add a state 
state |= stateOne;                // 18 | 1 = 19

//remove stateTwo from our state (if set)
if ((state & stateTwo) == stateTwo)
{
    state ^= stateTwo;           // 19 ^ 2 = 17
}

//check for a single state (while others might also be selected)
if ((state & stateOne) == stateOne)
{
    //stateOne is selected, do something
}

//check for a combination of states (while others might also be selected)
if ((state & (stateOne | stateTwo)) == stateOne | stateTwo)
{
    //stateOne and stateTwo are selected, do something
}

//the previous check is a lot nicer to read when using a mask (again)
FiveStateMask checkMask = stateOne | stateTwo;
if ((state & checkMask) == checkMask)
{
    //stateOne and stateTwo are selected, do something
}

回答2:

You can always use a byte (unsigned char) size variable using its' bits as flags (each bit acts as one BOOL flag).

Good instructions to set/clear/toggle/check a bit is here.

Offcourse you'd want to set kind of human readable names for this flags, i.e.:

#define flag1 1
#define flag2 2
#define flag3 4
#define flag4 8
#define flag5 16

回答3:

Nowadays we have got another option for flags. It is NS_ENUM.

typedef NS_ENUM(NSInteger, UITableViewCellStyle) {
    UITableViewCellStyleDefault,
    UITableViewCellStyleValue1,
    UITableViewCellStyleValue2,
    UITableViewCellStyleSubtitle
};

First arg for type and second for name.

来源：https://stackoverflow.com/questions/8956364/app-states-with-bool-flags

标签

objective-c

boolean

state

flags