NSNumber讲解之一——NSNumber封装数值型数据

学习目标
1. 掌握  NSNumber
2. 掌握  + numberWithXxx:、 - xxxValue、 
3. 了解 - initWithXxx
4. 了解  NSValues

学习过程
1. NSNumber用于封装OC基本数值型数据类型：
char, unsigned char, short, unsigned short, int, unsigned int,
long, unsigned long, long long, unsigned long long, float, double,
BOOL, NSInteger, NSUInteger   （提示BOOL型也是数值型，它只有1与0两个值）
2.+ numberWithXxx:      NSNumber的类方法
    - xxxValue                  NSNumber的实例方法
    - initWithXxx
       NSNumber的实例方法
以上xxx表示数值类型
原代码：

@interface NSNumber (NSNumberCreation)
- (NSNumber *)initWithChar:(char)value;
- (NSNumber *)initWithUnsignedChar:(unsigned char)value;
- (NSNumber *)initWithShort:(short)value;
- (NSNumber *)initWithUnsignedShort:(unsigned short)value;
- (NSNumber *)initWithInt:(int)value;
- (NSNumber *)initWithUnsignedInt:(unsigned int)value;
- (NSNumber *)initWithLong:(long)value;
- (NSNumber *)initWithUnsignedLong:(unsigned long)value;
- (NSNumber *)initWithLongLong:(long long)value;
- (NSNumber *)initWithUnsignedLongLong:(unsigned long long)value;
- (NSNumber *)initWithFloat:(float)value;
- (NSNumber *)initWithDouble:(double)value;
- (NSNumber *)initWithBool:(BOOL)value;
- (NSNumber *)initWithInteger:(NSInteger)value NS_AVAILABLE(10_5, 2_0);
- (NSNumber *)initWithUnsignedInteger:(NSUInteger)value NS_AVAILABLE(10_5, 2_0);

+ (NSNumber *)numberWithChar:(char)value;
+ (NSNumber *)numberWithUnsignedChar:(unsigned char)value;
+ (NSNumber *)numberWithShort:(short)value;
+ (NSNumber *)numberWithUnsignedShort:(unsigned short)value;
+ (NSNumber *)numberWithInt:(int)value;
+ (NSNumber *)numberWithUnsignedInt:(unsigned int)value;
+ (NSNumber *)numberWithLong:(long)value;
+ (NSNumber *)numberWithUnsignedLong:(unsigned long)value;
+ (NSNumber *)numberWithLongLong:(long long)value;
+ (NSNumber *)numberWithUnsignedLongLong:(unsigned long long)value;
+ (NSNumber *)numberWithFloat:(float)value;
+ (NSNumber *)numberWithDouble:(double)value;
+ (NSNumber *)numberWithBool:(BOOL)value;
+ (NSNumber *)numberWithInteger:(NSInteger)value NS_AVAILABLE(10_5, 2_0);
+ (NSNumber *)numberWithUnsignedInteger:(NSUInteger)value NS_AVAILABLE(10_5, 2_0);

@end

示例：
//main.m

#import <Foundation/Foundation.h>
/*演示+ numberWithXxx:、 - xxxValue*/
void f1() {
    NSNumber* p1 = [NSNumber numberWithInt:23];
    int i = [p1 intValue];
    NSLog(@"%d", i); //23

    
    NSNumber* p2 = [NSNumber numberWithBool:NO];
    BOOL b = [p2 boolValue];
    NSLog(@"%d", b); //0

    
    NSNumber* p3 = [NSNumber numberWithChar:'a'];
    char c = [p3 charValue];
    NSLog(@"%c", c);//a

    
    NSInteger x1 = 100;
    NSNumber* p4 = [NSNumber numberWithInteger:x1];
    NSInteger x2 = [p4 integerValue];
    NSLog(@"%ld", x2);//100
 }
/*演示initWithXxx (了解)*/

void f2() {
    NSNumber *number1 = [[NSNumber alloc] initWithInt:1000];
    int i = [number1 intValue];
    NSLog(@"%d", i);//1000

}
3. NSValues除了可以封装NSNumber封装的类型外，还可以封装
指针，结构体等任何自定义类型。具体知识点会在后期课程中学习
集合时再讲解

4. 凝问：NSNumber是否只能封装数值型的基本数据类型？

答： 是的。

5. 凝问：什么要使用NSValues与NSNumber？
答：1.为集合时使用
       2.为调用方法使用
       3.为系统封装的一些方法传参使用