1. 本地路径获取
a 总路径
NSString *homeDir = NSHomeDirectory();
b Documents 目录：这个目录用于存储用户数据或其它应该定期备份的信息。
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *docDir = [paths objectAtIndex:0];
c Library 目录：这个目录下有两个子目录：Caches 和 Preferences
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSLibraryDirectory, NSUserDomainMask, YES);
NSString *docDir = [paths objectAtIndex:0];
c.1 Preferences 目录：包含应用程序的偏好设置文件。不应该直接创建偏好设置文件，而是应该使用NSUserDefaults类来取得和设置应用程序的偏好。
[[NSUserDefaults standardUserDefaults] setObject:value forKey:defaultName];
[[NSUserDefaults standardUserDefaults] synchronize];
[[NSUserDefaults standardUserDefaults] stringArrayForKey:defaultName];
c.2 Caches 目录：用于存放应用程序专用的支持文件，保存应用程序再次启动过程中需要的信息。
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);
NSString *docDir = [paths objectAtIndex:0];
d tmp 目录：这个目录用于存放临时文件，保存应用程序再次启动过程中不需要的信息。
NSString *tmpDir = NSTemporaryDirectory();
2. 回到主线程的三种方法
a NSThread
[self performSelectorOnMainThread:@selector(updateUI) withObject:nil waitUntilDone:NO];
- (void)updateUI {
// UI
}
b NSOperationQueue
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
// UI
}];
c GCD
dispatch_async(dispatch_get_main_queue(), ^{
// UI
});
3. GCD操作相关的宏定义
//在Main线程上运行
#define DISPATCH_ON_MAIN_THREAD(mainQueueBlock) dispatch_async(dispatch_get_main_queue(), mainQueueBlock);
//在Global Queue上运行
#define DISPATCH_ON_GLOBAL_QUEUE_HIGH(globalQueueBlock) dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), globalQueueBlock);
#define DISPATCH_ON_GLOBAL_QUEUE_DEFAULT(globalQueueBlock) dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), globalQueueBlock);
#define DISPATCH_ON_GLOBAL_QUEUE_LOW(globalQueueBlock) dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0), globalQueueBlock);
#define DISPATCH_ON_GLOBAL_QUEUE_BACKGROUND(globalQueueBlock) dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), globalQueueBlock);
4. 计算文本宽度
UILabel *label = [[UILabel alloc] init];
label.numberOfLines = 0;
label.text = string;
label.font = [UIFont boldSystemFontOfSize:23];
[self.view addSubview:label];
CGSize size = [string boundingRectWithSize:CGSizeMake(200, CGFLOAT_MAX)
options:NSStringDrawingUsesFontLeading | NSStringDrawingUsesLineFragmentOrigin
attributes:@{NSFontAttributeName:label.font}
context:nil].size;
label.frame = CGRectMake(0, 0, size.width, size.height);
可以写一个NSString的分类:
- (CGSize)sizeForFont:(UIFont *)font width:(CGFloat)width
{
return [self boundingRectWithSize:CGSizeMake(width, CGFLOAT_MAX)
options:NSStringDrawingUsesFontLeading | NSStringDrawingUsesLineFragmentOrigin
attributes:@{NSFontAttributeName:font}
context:nil].size;
}
5. 修改系统UITableViewCell的imageView的大小
因为cell的imageView是readonly属性，不能修改。所以可以修改imageView.image的大小来改变imageView的大小。
// 设置cell图片大小
UIImage *cellImage = [UIImage imageNamed:@"cellImage"];
CGSize imageSize = CGSizeMake(40, 40);
UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0.0);
CGRect imageRect = CGRectMake(0.0, 0.0, imageSize.width, imageSize.height);
[cellImage drawInRect:imageRect];
cell.imageView.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
6.一行代码移除视图的所有子视图
[view.subviews makeObjectsPerformSelector:@selector(removeFromSuperview)];
