記錄一下日常開發(fā)中用到的一些比較偏的知識(shí)
GCC語法：
self.navigationItem.rightBarButtonItem = ({
UIBarButtonItem *rightItem = [[UIBarButtonItem alloc] initWithTitle:@"只看樓主" style:UIBarButtonItemStylePlain target:self action:@selector(onlyFollowLord:)];
[rightItem setTitleTextAttributes:@{NSFontAttributeName:font(14.0)} forState:UIControlStateNormal];
rightItem.tintColor = [UIColor textDarkGrayColor];
rightItem;
});
這個(gè)問題嚴(yán)格上講和Objective－C沒什么太大的關(guān)系煤杀，這個(gè)是GNU C的對(duì)C的擴(kuò)展語法 Xcode采用的Clang編譯眷蜈，Clang作為GCC的替代品，和GCC一樣對(duì)于GNU C語法完全支持
你可能知道if(condition)后面只能根一條語句沈自，多條語句必須用{}闊起來酌儒，這個(gè)語法擴(kuò)展即將一條(多條要用到{})語句外面加一個(gè)括號(hào)(), 這樣的話你就可以在表達(dá)式中應(yīng)用循環(huán)、判斷甚至本地變量等枯途。表達(dá)式()最后一行應(yīng)該一個(gè)能夠計(jì)算結(jié)果的子表達(dá)式加上一個(gè)分號(hào)(;), 這個(gè)子表達(dá)式作為整個(gè)結(jié)構(gòu)的返回結(jié)果
這個(gè)擴(kuò)展在代碼中最常見的用處在于宏定義中
用runtime實(shí)現(xiàn)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(類目)里的方法不需要導(dǎo)入頭文件就能執(zhí)行忌怎，比如修改父類方法時(shí)，不導(dǎo)入頭文件也能實(shí)現(xiàn)酪夷，如果要在category(類目)中加入新的方法或者屬性才需要導(dǎo)入頭文件榴啸。
子線程中要修改外界的值需要用到線程鎖，以防多處子線程同時(shí)修改同一值而造成閃退
問題代碼：
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];
}
});
}
修改后的代碼：
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);
});
}
合成圖片
- (UIImage *)imageWithName:(NSString *)name size:(CGSize)size {
//原圖
UIImage *image = [UIImage imageNamed:name];
//背景圖
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倒計(jì)時(shí)
-(void)startTimerBackZero:(NSInteger)time {
__block NSInteger timeout = time; //倒計(jì)時(shí)時(shí)間
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); //每秒執(zhí)行
dispatch_source_set_event_handler(_timer, ^{
if(timeout<=0){ //倒計(jì)時(shí)結(jié)束晚岭，關(guān)閉
dispatch_source_cancel(_timer);
dispatch_async(dispatch_get_main_queue(), ^{
//設(shè)置界面的按鈕顯示 根據(jù)自己需求設(shè)置
self.enabled = YES;
[self setTitle:@"重發(fā)驗(yàn)證碼" forState:UIControlStateNormal];
});
}else{
self.enabled = NO;
NSString *strTime = [NSString stringWithFormat:@"%ld秒后重獲",(long)timeout];
dispatch_async(dispatch_get_main_queue(), ^{
//設(shè)置界面的按鈕顯示 根據(jù)自己需求設(shè)置
[self setTitle:strTime forState:UIControlStateNormal];
});
timeout--;
}
});
dispatch_resume(_timer);
}
生成二維碼
// 創(chuàng)建過濾器
CIFilter *filter = [CIFilter filterWithName:@"CIQRCodeGenerator"];
// 恢復(fù)默認(rèn)
[filter setDefaults];
NSData *data = [self.shopURL dataUsingEncoding:NSUTF8StringEncoding];
[filter setValue:data forKeyPath:@"inputMessage"];
// 獲取輸出的二維碼
CIImage *outputImage = [filter outputImage];
// 將CIImage轉(zhuǎn)換成UIImage鸥印，并放大顯示
outputImage = [outputImage imageByApplyingTransform:CGAffineTransformMakeScale(150, 150)];
[UIImage imageWithCIImage:outputImage];
Autolayout的兩個(gè)屬性的使用說明
640254-97c4b2c919ac69d8.png.jpeg
“Content Compression Resistance Priority”，也叫內(nèi)容壓縮阻力優(yōu)先級(jí)（小名：別擠我）坦报，該優(yōu)先級(jí)越高库说，則越晚輪到被壓縮。
“Content Hugging Priority”片择，也叫內(nèi)容緊靠優(yōu)先級(jí)（小名：別扯我）潜的，該優(yōu)先級(jí)越高，這越晚輪到被拉伸构回。
漸變顏色
- (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;
}
