Objective-C: Check if using enum option

问题:

I have a custom object that is using a typedef enum. If I set a few of the enum options for my object, how can I check to see if those are being used?

typedef enum {
    Option1,
    Option2,
    Option3
} Options;

When creating my object I might use:

myobject.options = Option1 | Option2;

How can I then later check which enum options were set? Such as:

if (myobject.options == Option1) {
  // Do something
}

if (myobject.options == Option2) {
  // Do something
}

回答1:

If you want to do bitwise logic for your options parameter, then you should define your enum so that each option only has a single bit set:

typedef enum {
    Option1 = 1,       // 00000001
    Option2 = 1 << 1,  // 00000010
    Option3 = 1 << 2   // 00000100
} Options;

Then you set your options using the bitwise OR operator:

myObject.options = Option1 | Option2;

and check which options have been set using the bitwise AND operator:

if(myObject.options & Option1) {
    // Do something
}

回答2:

You shouldn't use an enum for this, or at least not use the standard numbering.

#define Option1 1
#define Option2 2
#define Option3 4
#define Option4 8
#define Option5 16

The values need to be powers of two, so you can combine them. A value of 3 means options 1 + 2 are chosen. You wouldn't be able to make that distinction if 3 was a valid value for one of the other options.

回答3:

I'd suggest to define the enum using NS_OPTIONS. This is the Apple recommended way to create such enums.

typedef NS_OPTIONS(NSUInteger, Options) {
    Options1 = 1 << 0,
    Options2 = 1 << 1,
    Options3 = 1 << 2,
};

Then, as it has already been said, you can assign values by doing:

myObject.options = Option1 | Option2;

and check them:

if (myObject.options & Option1) {
    // Do something
}

回答4:

if ((myobject.options & Option1) == Option1)