IOS – Writing high quality Objective-C methods efficiently (2) — Enumeration

As we continue our series of articles on Effective Objective-C, I’ll focus on enumerations. Enumerations are used a lot in OC, so do we really know what they are?

Because OC is based on C language, OC also has the enum function: enum.

Enumerations are used frequently in system frameworks, but they are easily overlooked by developers, and I often overlook them too.

Where are enumerations used?

Simple enumeration

For example, we use the following enumeration to represent network-state connections:

enum PPSConnectionState{
	PPSConnectionStateDisconnected,
	PPSConnectionStateConnecting,
	PPSConnectionStateConnected,
	};Copy the code

The code is easier to read because each enumeration is named so that we can easily understand what it represents. The compiler assigns each enumeration a unique number, starting at 0 and incrementing each enumeration by 1. The data type used to implement enumerations depends on the compiler, but the number of bits must be sufficient to fully represent the following enumeration numbers.

But if we define enumerations as above, then we define an enumeration variable as follows:

enum PPSConnectionState state = PPSConnectionStateConnected;Copy the code

We’re going to have to type enum every time and that’s a little bit cumbersome we’re going to type PPSConnectionState just like a normal object and if we’re going to do that we’re going to define enumerations using the typedef keyword

enum PPSConnectionState {
	PPSConnectionStateDisconnected,
	PPSConnectionStateConnecting,
	PPSConnectionStateConnected,
	};
typedef enum PPSConnectionState  PPSConnectionState;Copy the code

You can abbreviate it now:

PPSConnectionState state = PPSConnectionStateConnected;Copy the code

The C++11 standard revised several features of enumerations. One useful feature is that when we define an enumeration, we can define the underlying data type of the enumeration (used by the compiler to indicate the number of the enumeration) so that we can use forward-declared enumeration variables.

enum PPSConnectionState : NSInteger{ PPSConnectionStateDisconnected, PPSConnectionStateConnecting, PPSConnectionStateConnected, }; / / can also directly use enum PPSConnectionState {PPSConnectionStateDisconnected = 0, PPSConnectionStateConnecting, PPSConnectionStateConnected, };Copy the code

The underlying data type of the enumeration is the same in both ways. The first way the compiler assigns the enumeration to start at 0 by default. If we want our enumeration to start at 1, we can use the second way, which changes 0 to 1, and our enumeration will start at 1.

Combinatorial enumeration

enum UIViewAutoresizing{
	UIViewAutoresizingNone = 0,
	UIViewAutoresizingFlexibleLeftMargin  = 1 << 0,
	UIViewAutoresizingFlexibleWidth       = 1 << 1,
	UIViewAutoresizingFlexibleRightMargin = 1 << 2,
	...
	};Copy the code

enum UIViewAutoresizing resizing = UIViewAutoresizingFlexibleLeftMargin | UIViewAutoresizingFlexibleWidth;Copy the code

typedef NS_ENUM(NSUInteger, PPSConnectionState){
	PPSConnectionStateDisconnected,
	PPSConnectionStateConnecting,
	PPSConnectionStateConnected,
	};Copy the code

typedef NS_OPTION(NSUInteger, UIViewAutoresizing){
	UIViewAutoresizingNone = 0,
	UIViewAutoresizingFlexibleLeftMargin  = 1 << 0,
	UIViewAutoresizingFlexibleWidth       = 1 << 1,
	UIViewAutoresizingFlexibleRightMargin = 1 << 2,
	...
	};Copy the code

Pay attention to

In switch statements, we often use enumeration types, but we always like to use the default branch in switch statements. If we use enumeration, we don’t want to use the default branch, because if we add another state to the enumeration, Then we need to find every switch statement to process, otherwise we will go straight to the default branch and the compiler will run without any warning. But without the default branch, if we don’t change switch when we add enumeration types, the compiler will warn us at compile time that the enumeration is not completely judged.

conclusion