IOS开发实用技巧(一)

1.调试技巧重写description方法打印类的成员属性

#import <objc/runtime.h>
-(NSString *)description{
    unsigned int count = 0;
    NSMutableString *str = [NSMutableString string];
    Ivar *ivars = class_copyIvarList([self class], &count);
    for(int i =0;i < count;i ++)
    {
        Ivar ivar = ivars[i];
        NSString *ivarName = [NSString stringWithCString:ivar_getName(ivar) encoding:NSUTF8StringEncoding];
        id value = [self valueForKey:ivarName];
        //如果是最后一个变量去掉","
        if (i == count -1) {
            [str appendFormat:@"%@=%@",ivarName,value];
        }else{
         [str appendFormat:@"%@=%@,",ivarName,value];
        }
    }
    free(ivars);
    return [NSString stringWithFormat:@"%@{%@}",[super description],str];
}

2.自动归档解档

//存
- (void)encodeWithCoder:(NSCoder *)aCoder{
    unsigned int count = 0;
    Ivar *ivars = class_copyIvarList([TXModel class], &count);
    for (int i = 0; i < count; i++) {
        Ivar ivar = ivars[i];
        const char *name = ivar_getName(ivar);
        NSString *key = [NSString stringWithUTF8String:name];
        id value = [self valueForKey:key];
        [aCoder encodeObject:value forKey:key];
    }
    free(ivars);
}
//取
- (instancetype)initWithCoder:(NSCoder *)aDecoder{
    if (self = [super init]) {
        unsigned int count = 0;
        Ivar *ivars = class_copyIvarList([TXModel class], &count);
        for (int i = 0; i < count; i++) {
            Ivar ivar = ivars[i];
            const char *name = ivar_getName(ivar);
            NSString *key = [NSString stringWithUTF8String:name];
            id value = [aDecoder decodeObjectForKey:key];
            [self setValue:value forKey:key];
        }
        free(ivars);
    }
    return self;
}
```
>注意:通过上面的几个demo的演示,就不在此重复一些runtime的其他类似黑魔法了(获取方法/属性等等..)

3.拦截交换系统方法(NSObject加分类方法)
    用处:分类中最好是不能重写父类方法的,这时候要实现全局修改某个系统方法加上自己的逻辑判断,只能用交换系统的方法更好.
    还可以拦截系统奔溃.
```
@interface  UIView (MethodSwizzling)
/**
 *  交换对象方法
 */
+ (void)zh_swizzleInstanceSelector:(SEL)origSelector swizzleSelector:(SEL)swizzleSelector;
/**
 *  交换类方法
 */
+ (void)zh_swizzleClassSelector:(SEL)origSelector swizzleSelector:(SEL)swizzleSelector;
@end

@implementation  UIView (MethodSwizzling)

+ (void)zh_swizzleInstanceSelector:(SEL)origSelector swizzleSelector:(SEL)swizzleSelector {
    // 获取原有方法
    Method origMethod = class_getInstanceMethod(self,origSelector);
    // 获取交换方法
    Method swizzleMethod = class_getInstanceMethod(self,swizzleSelector);
    BOOL isAdd = class_addMethod(self, origSelector, method_getImplementation(swizzleMethod), method_getTypeEncoding(swizzleMethod));
    if (!isAdd) {
        method_exchangeImplementations(origMethod, swizzleMethod);
    }else {
        class_replaceMethod(self, swizzleSelector, method_getImplementation(origMethod), method_getTypeEncoding(origMethod));
    }
}
+ (void)zh_swizzleClassSelector:(SEL)origSelector swizzleSelector:(SEL)swizzleSelector
{
    // 获取原有方法
    Method origMethod = class_getClassMethod(self,origSelector);
    // 获取交换方法
    Method swizzleMethod = class_getClassMethod(self,swizzleSelector);
    // 添加原有方法实现为当前方法实现
    BOOL isAdd = class_addMethod(self, origSelector, method_getImplementation(swizzleMethod), method_getTypeEncoding(swizzleMethod));
    if (!isAdd) {
        method_exchangeImplementations(origMethod, swizzleMethod);
    }
}
```
>注意:实现load类方法 --- 类被加载运行的时候就会调用
当类加载进内存的时候调用，而且不管有没有子类，都只会调用一次，在main函数之前调用

```
+ (void)load
{
   [self zh_swizzleInstanceSelector:@selector( setBackgroundColor:)swizzleSelector:@selector( setMyBackgroundColor:)];
}
- (void)setMyBackgroundColor:(UIColor *)color{
    NSLog(@"%s",__FUNCTION__);
    //此处没有递归而是调用系统的setBackgroundColor
    [self setMyBackgroundColor:[UIColor orangeColor]];
}
```

4._cmd的一种巧妙用方法(分类中关联属性对象)

之前需要定义一个这样的const void *key,_cmd 是隐藏的参数，代表当前方法的 selector,可以代替这个key.
之前写法:
```
const void *webCacheKEY = "webCache";
-(void)setCurrentURL:(NSString *)currentURL{
//关联对象
    //参数1：要被关联的对象
    //参数2：关联的KEY
    //参数3：关联的值
    //参数4：关联策略(内存引用)
    objc_setAssociatedObject(self, webCacheKEY, currentURL, OBJC_ASSOCIATION_COPY);
}
-(NSString *)currentURL{
    //参数1：要被关联的对象
    //参数2：关联的KEY
    return objc_getAssociatedObject(self, webCacheKEY);
}
```
之后写法:
```
-(void)setCurrentURL:(NSString *)currentURL{
    objc_setAssociatedObject(self, _cmd, currentURL, OBJC_ASSOCIATION_COPY);
}

-(NSString *)currentURL{
    return objc_getAssociatedObject(self, _cmd);
}
```
5.背景渐变色
```
- (void)viewDidLoad {
    [super viewDidLoad];
    [self.view.layer addSublayer:[self backgroundLayer]];
}
//背景渐变色
-(CAGradientLayer *)backgroundLayer{
    CAGradientLayer *gradientLayer = [CAGradientLayer layer];
    gradientLayer.frame = self.view.bounds;
    gradientLayer.colors = @[(__bridge id)[UIColor purpleColor].CGColor,(__bridge id)[UIColor redColor].CGColor];
    gradientLayer.startPoint = CGPointMake(0.5, 0);
    gradientLayer.endPoint = CGPointMake(0.5, 1);
    gradientLayer.locations = @[@0.65,@1];
    return gradientLayer;
}
```
6.调试代码执行时间
```
#define TICK   NSDate *startTime = [NSDate date];
#define TOCK   NSLog(@"Time: %f", -[startTime timeIntervalSinceNow]);
TICK
// 代码块
TOCK
```
7.程序启动过程中各个阶段所消耗的时间
   在工程的scheme中添加环境变量DYLD_PRINT_STATISTICS = 1,这样在调试时，可以在控制台打印出程序启动过程中各个阶段所消耗的时间。


8.KVC集合运算符
   KVC集合运算符允许在valueForKeyPath:方法中使用key path符号在一个集合中执行方法。可以直接求出总数/最大值/最小值/平均值
```
@interface TestModel : NSObject
@property (nonatomic, assign) double price;
@end

- (void)viewDidLoad {
    [super viewDidLoad];
     NSArray *priceArray = @[@"1",@"2",@"3",@"4",@"5"];
     NSMutableArray *dataArray = [NSMutableArray array];
     for (NSInteger i = 0; i < priceArray.count; ++i) {
        TestModel *testModel = [[TestModel alloc] init];
        testModel.price = [priceArray[i] doubleValue];
        [dataArray addObject:testModel];
    }
    id count1 = [dataArray valueForKeyPath:@"@count"];     // 5
    id count2 = [dataArray valueForKeyPath:@"@sum.price"]; // 15
    id count3 = [dataArray valueForKeyPath:@"@avg.price"]; // 3
    id count4 = [dataArray valueForKeyPath:@"@max.price"]; // 5
    id count5 = [dataArray valueForKeyPath:@"@min.price"]; // 1
    NSLog(@"%@,%@,%@,%@,%@",count1,count2,count3,count4,count5);

    NSArray *array = [NSArray arrayWithObjects:@"2.0", @"2.3", @"3.0", @"4.0", @"10", nil];
    id sum = [array valueForKeyPath:@"@sum.floatValue"];
    id avg = [array valueForKeyPath:@"@avg.floatValue"];
    id max = [array valueForKeyPath:@"@max.floatValue"];
    id min = [array valueForKeyPath:@"@min.floatValue"];
    NSLog(@"%@,%@,%@,%@",sum,avg,max,min);
}
```
9.抗锯齿的两种方法
第一种:
```
    self.view.layer.allowsEdgeAntialiasing = YES;
```
 第二种:
```
    self.view.layer.borderColor = [UIColorclearColor].CGColor;
    self.view.layer.borderWidth = 1.f;
```
10.调节UINavigationBar的leftBarButtonItem离左边的距离
```
    UIBarButtonItem *buttonItem = [[UIBarButtonItem alloc] initWithImage:[UIImage imageNamed:@"back-button-whiteArrow.png"] style:UIBarButtonItemStylePlain target:self action:@selector(logoutBarBtnPressed:)];
    UIBarButtonItem *fixedBarButtonItem = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFixedSpace target:nil action:nil];
    fixedBarButtonItem.width = -15;
    self.navigationItem.leftBarButtonItems = [NSArray arrayWithObjects:fixedBarButtonItem, buttonItem, nil];
```