iOS一些知识点

1. 给一个view截图

    UIGraphicsBeginImageContextWithOptions(view.bounds.size, YES, 0.0);
    [view.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

2. 颜色转图片

 + (UIImage *)dl_imageWithColor:(UIColor *)color {
    CGRect rect = CGRectMake(0.0f, 0.0f, 1.0f, 1.0f);
    UIGraphicsBeginImageContext(rect.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    
    CGContextSetFillColorWithColor(context, [color CGColor]);
    CGContextFillRect(context, rect);
    
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return image;
}

3. 监听用户修改了本地时间

NSSystemTimeZoneDidChangeNotification监听修改时间界面的两个按钮状态变化
UIApplicationSignificantTimeChangeNotification 监听用户改变时间 （只要点击自动设置按钮就会调用） 
NSSystemClockDidChangeNotification 监听用户修改时间（时间不同才会调用）

4. collectionView的内容小于其宽高的时候是不能滚动的，设置可以滚动：

collectionView.alwaysBounceHorizontal = YES;
collectionView.alwaysBounceVertical = YES;

5. 修改NSLog

#ifdef DEBUG
#define NSLog(fmt, ...) NSLog((@"%s [Line %d] " fmt), __PRETTY_FUNCTION__, __LINE__, ##__VA_ARGS__)
#else
#define NSLog(...)
#endif

6. 长按复制

 - (void)viewDidLoad
{
    [self.view addGestureRecognizer:[[UILongPressGestureRecognizer alloc] initWithTarget:self action:@selector(pasteBoard:)]];
}
 - (void)pasteBoard:(UILongPressGestureRecognizer *)longPress {
    if (longPress.state == UIGestureRecognizerStateBegan) {
        UIPasteboard *pasteboard = [UIPasteboard generalPasteboard];
        pasteboard.string = @"需要复制的文本";
    }
}

7. 获取userAgent

+(NSString*)userAgent
{
    static NSString *userAgent = @"";
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        userAgent = [[UIWebView new] stringByEvaluatingJavaScriptFromString:@"navigator.userAgent"];
    });
    return userAgent;
}

8. afnetworking 过滤NSNULL

AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
    
    AFJSONResponseSerializer *serializer = [AFJSONResponseSerializer serializer];
    serializer.removesKeysWithNullValues = YES;
    manager.responseSerializer = serializer;

8. 修改UITextfile ，UISearchBar的placehold的fontColor

UITextField *searchField = [searchBar valueForKey:@"_searchField"]; 
[searchField setValue:[UIColor blueColor] forKeyPath:@"_placeholderLabel.textColor"];

9. 禁止同时点点击多个控件，避免同时响应多个事件

// UIView有个属性叫做exclusiveTouch，设置为YES后，其响应事件会和其他view互斥(有其他view事件响应的时候点击它不起作用) 
view.exclusiveTouch = YES; // 一个一个设置太麻烦了，可以全局设置 
[[UIView appearance] setExclusiveTouch:YES]; // 或者只设置button 
[[UIButton appearance] setExclusiveTouch:YES];