记录iOS开发中的一些小技巧（一）

记录一下日常开发中用到的一些比较偏的知识

GCC语法：

self.navigationItem.rightBarButtonItem = ({

     UIBarButtonItem *rightItem = [[UIBarButtonItem alloc] initWithTitle:@"只看楼主" style:UIBarButtonItemStylePlain target:self action:@selector(onlyFollowLord:)];

     [rightItem setTitleTextAttributes:@{NSFontAttributeName:font(14.0)} forState:UIControlStateNormal];

     rightItem.tintColor = [UIColor textDarkGrayColor];

     rightItem;

});
这个问题严格上讲和Objective－C没什么太大的关系，这个是GNU C的对C的扩展语法 Xcode采用的Clang编译，Clang作为GCC的替代品，和GCC一样对于GNU C语法完全支持

你可能知道if(condition)后面只能根一条语句，多条语句必须用{}阔起来，这个语法扩展即将一条(多条要用到{})语句外面加一个括号(), 这样的话你就可以在表达式中应用循环、判断甚至本地变量等。表达式()最后一行应该一个能够计算结果的子表达式加上一个分号(;), 这个子表达式作为整个结构的返回结果

这个扩展在代码中最常见的用处在于宏定义中

用runtime实现model序列化：

- (instancetype)initWithCoder:(NSCoder *)aDecoder {

     if (self = [super init]) {

          unsigned int count = 0;

          Ivar *ivar = class_copyIvarList([self class], &count);

          for (int i = 0; i<count; i++) {

               Ivar iva = ivar[i];

               const char *name = ivar_getName(iva);

               NSString *strName = [NSString stringWithUTF8String:name];

               id value = [aDecoder decodeObjectForKey:strName];

               [self setValue:value forKey:strName];
          }
          free(ivar);
     }
     return self;
}

- (void)encodeWithCoder:(NSCoder *)aCoder {

     unsigned int count;

     Ivar *ivar = class_copyIvarList([self class], &count);

     for (int i=0; i < count; i++) {

          Ivar iv = ivar[i];

          const char *name = ivar_getName(iv);

          NSString *strName = [NSString stringWithUTF8String:name];

          id value = [self valueForKey:strName];

          [aCoder encodeObject:value forKey:strName];

     }

     free(ivar);

}

工程中的category(类目)里的方法不需要导入头文件就能执行，比如修改父类方法时，不导入头文件也能实现，如果要在category(类目)中加入新的方法或者属性才需要导入头文件。

子线程中要修改外界的值需要用到线程锁，以防多处子线程同时修改同一值而造成闪退

问题代码：

NSMutableArray *array = [NSMutableArray arrayWithObjects:@"haha", nil];

//并行

dispatch_queue_t queue = dispatch_queue_create(DISPATCH_QUEUE_PRIORITY_DEFAULT, DISPATCH_QUEUE_CONCURRENT);

for (int i = 0 ;i < 2 ; i++ ) {

     dispatch_async(queue, ^{

               if (array.count > 0) {
     
               [array removeObjectAtIndex:0];

          }

     });

}

修改后的代码：

NSMutableArray *array = [NSMutableArray arrayWithObjects:@"haha", nil];

//并行

dispatch_queue_t queue = dispatch_queue_create(DISPATCH_QUEUE_PRIORITY_DEFAULT, DISPATCH_QUEUE_CONCURRENT);

dispatch_semaphore_t semaphore = dispatch_semaphore_create(1);

for (int i = 0 ;i < 2 ; i++ ) {

     dispatch_async(queue, ^{

     dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);

     if (array.count > 0) {

          [array removeObjectAtIndex:0];

     }

     dispatch_semaphore_signal(semaphore);

     });

}

合成图片

- (UIImage *)imageWithName:(NSString *)name size:(CGSize)size {
    //原图
    UIImage *image = [UIImage imageNamed:name];
    //背景图
    UIImage *backImage = [image imageWithTintColor:[UIColor colorWithHexString:@"#f39004"]];
    UIGraphicsBeginImageContextWithOptions(size, NO, image.scale);
    
    [backImage drawInRect:(CGRect){CGPointZero,size}];
    [image drawInRect:(CGRect){(size.width - image.size.width) / 2,(size.height - image.size.height) / 2,image.size.width,image.size.height}];
    //合成
    UIImage *newsImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    return newsImage;
}

用GCD倒计时

-(void)startTimerBackZero:(NSInteger)time {
    __block NSInteger timeout = time; //倒计时时间
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_source_t _timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0,queue);
    dispatch_source_set_timer(_timer,dispatch_walltime(NULL, 0),1ull*NSEC_PER_SEC, 0); //每秒执行
    dispatch_source_set_event_handler(_timer, ^{
        if(timeout<=0){ //倒计时结束，关闭
            dispatch_source_cancel(_timer);
            dispatch_async(dispatch_get_main_queue(), ^{
                //设置界面的按钮显示 根据自己需求设置
                self.enabled = YES;
                [self setTitle:@"重发验证码" forState:UIControlStateNormal]; 
            });
        }else{ 
            self.enabled = NO;
            NSString *strTime = [NSString stringWithFormat:@"%ld秒后重获",(long)timeout];
            dispatch_async(dispatch_get_main_queue(), ^{
                //设置界面的按钮显示 根据自己需求设置
                [self setTitle:strTime forState:UIControlStateNormal];
            });
            timeout--; 
        }
    });
    dispatch_resume(_timer);
}

生成二维码

// 创建过滤器
    CIFilter *filter = [CIFilter filterWithName:@"CIQRCodeGenerator"];
    // 恢复默认
    [filter setDefaults];
    NSData *data = [self.shopURL dataUsingEncoding:NSUTF8StringEncoding];
    [filter setValue:data forKeyPath:@"inputMessage"];
    // 获取输出的二维码
    CIImage *outputImage = [filter outputImage];
    // 将CIImage转换成UIImage，并放大显示
    outputImage = [outputImage imageByApplyingTransform:CGAffineTransformMakeScale(150, 150)];
    [UIImage imageWithCIImage:outputImage];

Autolayout的两个属性的使用说明

640254-97c4b2c919ac69d8.png.jpeg

“Content Compression Resistance Priority”，也叫内容压缩阻力优先级（小名：别挤我），该优先级越高，则越晚轮到被压缩。

“Content Hugging Priority”，也叫内容紧靠优先级（小名：别扯我），该优先级越高，这越晚轮到被拉伸。

渐变颜色

- (CAGradientLayer *)shadowAsInverse {
    CAGradientLayer *layer = [[CAGradientLayer alloc] init];
    CGRect rect = _imageView.bounds;
    layer.frame = rect;
    layer.colors = [NSArray arrayWithObjects:(id)[UIColor yellowColor].CGColor,(id)[UIColor redColor].CGColor, nil];
    layer.startPoint = CGPointMake(0, 0);
    layer.endPoint = CGPointMake(1, 0);
    layer.cornerRadius = 64;
    return layer;
}