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;
}
