iOS－－小知识点（持续更新）

太过爱你忘了你带给我的痛 2022-09-30 12:50 403阅读 0赞

#### 一. 颜色渐变 ####

CAGradientLayer *gradientLayer = [CAGradientLayer layer];
        gradientLayer.colors = @[(__bridge id)[UIColor whiteColor].CGColor, (__bridge id)[UIColor grayColor].CGColor, (__bridge id)[UIColor whiteColor].CGColor];
        gradientLayer.locations = @[@0.0, @0.5, @1.0];
        gradientLayer.startPoint = CGPointMake(0, 0);
        gradientLayer.endPoint = CGPointMake(1.0, 0);
        gradientLayer.frame = CGRectMake(0, 100, 300, 2);
        [self.view.layer addSublayer:gradientLayer];

#### 二. （已删除） ####

#### 三. 使用drowRect绘制简单图形 ####

//获取上下文
        CGContextRef context=UIGraphicsGetCurrentContext();
        //设置绘制地区的颜色
        CGContextSetRGBFillColor(context, 1, 0, 0, 1);
        //设置绘制的位置和大小
        CGContextFillRect(context, CGRectMake(0, 100, 100, 100));
        NSString * text=@"文字";
        UIFont * font=[UIFont systemFontOfSize:14];
        //设置文字的位置
        [text drawAtPoint:CGPointMake(0, 200) withAttributes:font.fontDescriptor.fontAttributes];
        UIImage * img=[UIImage imageNamed:@""];
        [img drawInRect:CGRectMake(0, 300, 100, 100)];

#### 四. 可变数组与不可变数组之间的转换 ####

NSMutableArray * mutablearray=[[NSMutableArray alloc]initWithCapacity:0];
        NSArray * copyarray=[mutablearray copy];
        copyarray=@[@"1",@"2",@"3"];
        NSArray * array=[[NSArray alloc]init];
        NSMutableArray * copymutablearray=[array mutableCopy];
    
        [copymutablearray setObject:@"加入到第一位" atIndexedSubscript:0];
        [copymutablearray addObject:@"排序加入"];
        [copymutablearray addObjectsFromArray:copyarray];

#### 五. 快速求和，最大值，最小值，平均值 ####

NSArray *array = [NSArray arrayWithObjects:@"2.0", @"2.3", @"3.0", @"4.0", @"10", nil];
        CGFloat sum = [[array valueForKeyPath:@"@sum.floatValue"] floatValue];
        CGFloat avg = [[array valueForKeyPath:@"@avg.floatValue"] floatValue];
        CGFloat max =[[array valueForKeyPath:@"@max.floatValue"] floatValue];
        CGFloat min =[[array valueForKeyPath:@"@min.floatValue"] floatValue];

#### 六. 对控件的旋转，平移，缩放，复位 ####

//平移
          CGAffineTransform transForm = _pingyibu.transform;
         _pingyibu.transform=CGAffineTransformTranslate(transForm, 100, 0);
        //旋转
        _pingyibu.transform = CGAffineTransformRotate(transForm, M_PI_4);
        //缩放按钮
        _pingyibu.transform = CGAffineTransformScale(transForm, 1.2, 1.2);
        //初始化复位
         _pingyibu.transform = CGAffineTransformIdentity;

#### 七. 设置label的行间距 ####

NSMutableAttributedString *attributedString =
        [[NSMutableAttributedString alloc] initWithString:_xuanzhuanla.text];
        NSMutableParagraphStyle *paragraphStyle =  [[NSMutableParagraphStyle alloc] init];
        [paragraphStyle setLineSpacing:3];
        //调整行间距
        [attributedString addAttribute:NSParagraphStyleAttributeName
                                 value:paragraphStyle
                                 range:NSMakeRange(0, [_xuanzhuanla.text length])];
        _xuanzhuanla.attributedText = attributedString;

#### 八. 让应用直接闪退 ####

AppDelegate *app = [UIApplication sharedApplication].delegate;
        UIWindow *window = app.window;
        [UIView animateWithDuration:1.0f animations:^{
            window.alpha = 0;
        } completion:^(BOOL finished) {
            exit(0);
        }];

#### 九. 手机震动 ####

AudioServicesPlaySystemSound(kSystemSoundID_Vibrate);

#### 十. 生成手机唯一ID：UUID ####

-(NSString*) uuid {
        CFUUIDRef puuid = CFUUIDCreate( nil );
        CFStringRef uuidString = CFUUIDCreateString( nil, puuid );
        NSString * result = (NSString *)CFBridgingRelease(CFStringCreateCopy( NULL, uuidString));
        CFRelease(puuid);
        CFRelease(uuidString);
        return result;
    }

#### 十一. label自适应高度 ####

CGRect rect=[la.text boundingRectWithSize:CGSizeMake(WIDTH-70, MAXFLOAT) options:NSStringDrawingUsesLineFragmentOrigin|NSStringDrawingUsesFontLeading attributes:@{NSFontAttributeName:la.font} context:nil];

#### 十二. 使用AFN判断网络状态 ####

NSURL *url=[NSURL URLWithString:@"http://www.apple.com"];
        AFHTTPRequestOperationManager *operationManager=[[AFHTTPRequestOperationManager alloc]initWithBaseURL:url];
        //根据不同的网络状态改变去做相应处理
        [operationManager.reachabilityManager setReachabilityStatusChangeBlock:^(AFNetworkReachabilityStatus status) {
                   switch (status) {
                case AFNetworkReachabilityStatusReachableViaWWAN:
                    [self fasongsuoyou];
                    break;
                case AFNetworkReachabilityStatusReachableViaWiFi:
                           [self fasongsuoyou];
                    break;
                case AFNetworkReachabilityStatusNotReachable:
                    [self alert:NSLocalizedString(@"wuwangluo",@"")];
                    break;
                default:
                    break;
            }
        }];
        //开始监控
        [operationManager.reachabilityManager startMonitoring];

#### 十三. image转换成data类型 ####

NSData *data=UIImagePNGRepresentation(image);
    NSData *data=UIImageJPEGRepresentation(image, 1.0);

#### 十四. 获取当前时间和时间戳 ####

//当前时间
    NSDate *  senddate=[NSDate date];
            NSDateFormatter  *dateformatter=[[NSDateFormatter alloc] init];
            [dateformatter setDateFormat:@"YYYY-MM-dd HH:mm:ss"];
    NSString * locationString=[dateformatter stringFromDate:senddate];
    //当前时间戳
    NSDate* dat = [NSDate dateWithTimeIntervalSinceNow:0];
            NSTimeInterval a=[dat timeIntervalSince1970];
            NSString *timeString = [NSString stringWithFormat:@"%f", a];
            long s = [timeString intValue];

#### 十五. 对比时间差 ####

-(int)max:(NSDate *)datatime
    {
        //创建日期格式化对象
        NSDateFormatter *dateFormatter=[[NSDateFormatter alloc] init];
        [dateFormatter setDateFormat:@"YYYY-MM-dd hh:mm:ss"];
        NSDate *  senddate=[NSDate date];
        NSString *  locationString=[dateFormatter stringFromDate:senddate];
        NSDate *date=[dateFormatter dateFromString:locationString];
        //取两个日期对象的时间间隔：
        //这里的NSTimeInterval 并不是对象，是基本型，其实是double类型，是由c定义的:typedef double NSTimeInterval;
        NSTimeInterval time=[date timeIntervalSinceDate:datatime];
        int days=((int)time)/(3600*24);
        return days;
    }

#### 十六. 使提示框消失（定时） ####

[alu dismissWithClickedButtonIndex:0 animated:NO];

#### 十七. 设置self.title的颜色 ####

UIColor * color=[UIColor whiteColor];
    NSDictionary * dict=[NSDictionary dictionaryWithObject:color forKey:UITextAttributeTextColor];
    self.navigationController.navigationBar.titleTextAttributes = dict;

#### 十八. 请求定位权限以及定位属性 ####

//定位管理器
        _locationManager=[[CLLocationManager alloc]init];
        //如果没有授权则请求用户授权
        if ([CLLocationManager authorizationStatus]==kCLAuthorizationStatusNotDetermined){
            [_locationManager requestWhenInUseAuthorization];
        }else if([CLLocationManager authorizationStatus]==kCLAuthorizationStatusAuthorizedWhenInUse){
            //设置代理
            _locationManager.delegate=self;
            //设置定位精度
            _locationManager.desiredAccuracy=kCLLocationAccuracyBest;
            //定位频率,每隔多少米定位一次
            CLLocationDistance distance=10.0;//十米定位一次
            _locationManager.distanceFilter=distance;
            //启动跟踪定位
            [_locationManager startUpdatingLocation];
        }

#### 十九. 通过经纬度计算距离 ####

BOOL JuLi=NO;
        CLLocation *orig=[[CLLocation alloc] initWithLatitude:oldlat  longitude:oldlong];
        CLLocation* dist=[[CLLocation alloc] initWithLatitude:nowlat longitude:nowlong];
        CLLocationDistance kilometers=[orig distanceFromLocation:dist];
        NSLog(@"距离:%f",kilometers);
        if (kilometers>=10) {
            JuLi=YES;
        }
        else{
            JuLi=NO;
        }
        return JuLi;

#### 二十. 弹出效果 ####

/** * 弹出对话框的动画 * * @param changeOutView 要执行的view * @param dur 动画时长 */
    -(void)exChangeOut:(UIView *)changeOutView dur:(CFTimeInterval)dur{
        CAKeyframeAnimation * animation;
        animation = [CAKeyframeAnimation animationWithKeyPath:@"transform"];
        animation.duration = dur;
        //animation.delegate = self;
        animation.removedOnCompletion = NO;
        animation.fillMode = kCAFillModeForwards;
        NSMutableArray *values = [NSMutableArray array];
        [values addObject:[NSValue valueWithCATransform3D:CATransform3DMakeScale(0.1, 0.1, 1.0)]];
        [values addObject:[NSValue valueWithCATransform3D:CATransform3DMakeScale(1.2, 1.2, 1.0)]];
        [values addObject:[NSValue valueWithCATransform3D:CATransform3DMakeScale(0.9, 0.9, 0.9)]];
        [values addObject:[NSValue valueWithCATransform3D:CATransform3DMakeScale(1.0, 1.0, 1.0)]];
        animation.values = values;
        animation.timingFunction = [CAMediaTimingFunction functionWithName: @"easeInEaseOut"];
        [changeOutView.layer addAnimation:animation forKey:nil];
    }

#### 二十一. 设置TextField左右视图 ####

-(id)initWithFrame:(CGRect)frame drawingLeft:(UIImageView *)icon drawingRight:(UIButton *)bu{
        self = [super initWithFrame:frame];
        if (self) {
            self.leftView = icon;
            self.leftViewMode = UITextFieldViewModeAlways;
            self.rightView= bu;
            self.rightViewMode=UITextFieldViewModeAlways;
        }
        return self;
    }
    -(CGRect)leftViewRectForBounds:(CGRect)bounds{
        CGRect iconRect = [super leftViewRectForBounds:bounds];
        iconRect.origin.x += 5;// 右偏10
        return iconRect;
    }
    -(CGRect)rightViewRectForBounds:(CGRect)bounds
    {
        CGRect burect=[super rightViewRectForBounds:bounds];
        burect.origin.x +=-10;
        return burect;
    }

#### 二十二. 常用宏定义 ####

#define PUSH(x) AppDelegate *appdelegate=(AppDelegate *)[UIApplication sharedApplication].delegate;[(UINavigationController*)appdelegate.window.rootViewController pushViewController:x animated:YES];
    
    #define POP AppDelegate *appdelegate=(AppDelegate *)[UIApplication sharedApplication].delegate;[(UINavigationController*)appdelegate.window.rootViewController popViewControllerAnimated:YES];
    
    #define POPROOT OGPAppDelegate *appdelegate=(OGPAppDelegate *)[UIApplication sharedApplication].delegate;[(UINavigationController*)appdelegate.window.rootViewController popToRootViewControllerAnimated:YES];
    
    #define IOS7 ([[UIDevice currentDevice].systemVersion floatValue] >= 7.0f)
    #define IPHONE_4INCH ([UIScreen mainScreen].bounds.size.height > 480.0f)

#### 二十三. 获取版本号提示版本更新 ####

-(void)VersionButton
    {
        NSString * string=[NSString stringWithContentsOfURL:[NSURL URLWithString:@"http://itunes.apple.com/lookup?id=??????????"] encoding:NSUTF8StringEncoding error:nil];
        if (string!=nil && [string length]>0 && [string rangeOfString:@"version"].length==7) {
            [self checkenAppUpdate:string];
        }
    }
    -(void)checkenAppUpdate:(NSString *)appinfo
    {
        NSString * version=[[[NSBundle mainBundle] infoDictionary] objectForKey:@"CFBundleVersion"];
        NSString * appInfo1=[appinfo substringFromIndex:[appinfo rangeOfString:@"\"version\":"].location+10];
        appInfo1=[[appInfo1 substringToIndex:[appInfo1 rangeOfString:@","].location] stringByReplacingOccurrencesOfString:@"\"" withString:@""];
        if (![appInfo1 isEqualToString:version]) {
            UIAlertView * alert=[[UIAlertView alloc]initWithTitle:@"" message:[NSString stringWithFormat:@"新版本%@, 已经发布",appInfo1] delegate:self cancelButtonTitle:@"知道了" otherButtonTitles: nil];
            alert.delegate=self;
            [alert addButtonWithTitle:@"前往更新"];
            [alert show];
            alert.tag=20;
        }
    }
    -(void)alertView:(UIAlertView *)alertView didDismissWithButtonIndex:(NSInteger)buttonIndex
    {
        if (buttonIndex==1 & alertView.tag==20) {
            NSString * url=@"https://appsto.re/cn/-naScb.i";
            [[UIApplication sharedApplication] openURL:[NSURL URLWithString:url]];
        }
    }

#### 二十四. 获取设备或APP信息 ####

//返回应用程序名称
    +(NSString *) getAppName{
        NSDictionary *infoDictionary = [[NSBundle mainBundle] infoDictionary];
        return [infoDictionary objectForKey:@"CFBundleDisplayName"];
    }
    //返回应用版本号
    +(NSString *) getAppVersion{
        NSDictionary *infoDictionary = [[NSBundle mainBundle] infoDictionary];
        return [infoDictionary objectForKey:@"CFBundleShortVersionString"];
    }
    +(NSString *) getAppBundleVersion{
        NSDictionary *infoDictionary = [[NSBundle mainBundle] infoDictionary];
        return [infoDictionary objectForKey:@"CFBundleVersion"];
    }
    //设备型号
    +(NSString *) getSystemName{
        return [[UIDevice currentDevice] systemName];
    }
    //设备版本号
    +(NSString *) getSystemVersion{
        return [[UIDevice currentDevice] systemVersion];
    }

#### 二十五. 内存泄漏分析 ####

静态分析内存泄露 使用Xcode自带的Analyze功能（Product-> Analyze）（Shift + Command + B），对代码进行静态分析，对于内存泄露（Potential Memory Leak）, 未使用局部变量(dead store)，逻辑错误(Logic Flaws)以及API使用问题(API-usage)等明确的展示出来。 静态分析的内存泄露情况比较简单，开发者都能很快的解决。这里不做赘述。 动态分析内存泄露 使用Xcode自带的Profile功能（Product-> Profile）（Command + i）弹出工具框，选择Leaks打开，选择运行设备点左上角的Record录制按钮，项目就会在已选好的设备上运行，并开始录制内存检测情况。选Leaks查看泄露情况，在Leaks的详细菜单Details选项里选调用树Call Tree，可查看所有内存泄露发生在哪些地方。再在右侧的齿轮设置-Call Tree-勾选Hide System Libraries，则可直接看内存泄露发生的函数名、方法名。点击函数名、方法名，可直接跳到函数方法的细节，可以看到哪一句代码出现了内存泄露，以及泄露了多少内存。

接下来就要回到Xcode，找到出现内存泄露的函数方法，仔细分析如何出现的内存泄露; 一般使用ARC，按照上面一提到的内存理解和编码习惯是不会出现内存泄露的。但我们在开发过程中，经常要使用第三方的一些类库，特别是涉及到加密的类库，用c或c++来编码的加密解密方法，会出现内存泄露。此时，我们要明白这些内存分配，需要手动释放。要一步一步看，哪里分配了内存，在使用完之后一定要记得释放free它。

#### 二十六. block循环利用导致内存泄漏 ####

A *a = [[A alloc] init]; 
    a.finishBlock = ^(NSDictionary paraments){ [a doSomething]; }; 对于这种在block块里引用对象a的情况，要在创建对象a时加修饰符block来防止循环引用。 
    block A *a = [[A alloc] init]; 
    a.finishBlock = ^(NSDictionary paraments){ [a doSomething]; }; 或
     A __block a = [[A alloc] init]; a.finishBlock = ^(NSDictionary paraments){ [a doSomething]; };
     或者，需要在block中调用用self的方法、属性、变量时，可以这样写
    __weak typeof(self) weakSelf = self;
    在block中使用weakSelf。 
    __weak typeof(self) weakSelf = self;
     [b doSomethingWithFinishBlock:^{ weakSelf.text = @"内存检测"; [weakSelf doSomething]; }];

#### 二十七. label 的空格属性和局部字段颜色 ####

设置 label 的 autoresizingMask 为 NO ,可以使用空格间隔字符串!
    
        NSMutableAttributedString *hintString=[[NSMutableAttributedString alloc]initWithString:@"点击注册按钮服务协议"];  
        //获取要调整颜色的文字位置,调整颜色 
        NSRange range1=[[hintString string]rangeOfString:@"注册"];  
        [hintString addAttribute:NSForegroundColorAttributeName value:[UIColor greenColor] range:range1];  
        NSRange range2=[[hintString string]rangeOfString:@"服务协议"];  
        [hintString addAttribute:NSForegroundColorAttributeName value:[UIColor redColor] range:range2];  
        hintLabel.attributedText=hintString;

#### 二十八. 过滤特殊字符 ####

// 定义一个特殊字符的集合
        NSCharacterSet *set = [NSCharacterSet characterSetWithCharactersInString:
        @"@／：；（）¥「」＂、[]{}#%-*+=_\\|~＜＞$€^•'@#$%^&*()_+'\""];
        // 过滤字符串的特殊字符
        NSString *newString = [trimString stringByTrimmingCharactersInSet:set];

#### 二十九. 设置滑动的时候隐藏 navigationbar ####

第1种:
            navigationController.hidesBarsOnSwipe = Yes
    
        第2种:
            //1.当我们的手离开屏幕时候隐藏
        - (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset
        { 
            if(velocity.y > 0) 
            {
            [self.navigationController setNavigationBarHidden:YES animated:YES];
            } else {
            [self.navigationController setNavigationBarHidden:NO animated:YES]; 
            }
        }
        velocity.y这个量，在上滑和下滑时，变化极小（小数），但是因为方向不同，有正负之分，这就很好处理  了。

#### 三十. 屏幕截图 ####

// 1. 开启一个与图片相关的图形上下文
        UIGraphicsBeginImageContextWithOptions(self.view.bounds.size,NO,0.0);
        // 2. 获取当前图形上下文
        CGContextRef ctx = UIGraphicsGetCurrentContext();
        // 3. 获取需要截取的view的layer
        [self.view.layer renderInContext:ctx];
        // 4. 从当前上下文中获取图片
        UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
        // 5. 关闭图形上下文
        UIGraphicsEndImageContext();
        // 6. 把图片保存到相册
        UIImageWriteToSavedPhotosAlbum(image, nil, nil, nil);

#### 三十一. 去掉 tabbar 和 navgationbar 的黑线 ####

//去掉tabBar顶部线条
        CGRect rect = CGRectMake(0, 0, 1, 1);
        UIGraphicsBeginImageContext(rect.size);
        CGContextRef context = UIGraphicsGetCurrentContext();
        CGContextSetFillColorWithColor(context, [[UIColor clearColor] CGColor]);
        CGContextFillRect(context, rect);
        UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
        [self.tabBar setBackgroundImage:img];
        [self.tabBar setShadowImage:img];
        //[self.navigationController.navigationBar setBackgroundImage:img];
        //self.navigationController.navigationBar.shadowImage = ima;
    
        self.tabBar.backgroundColor = SLIVERYCOLOR;

#### 三十二. 判断字符串中是否含有中文 ####

-(BOOL)isChinese:(NSString *)str{
            NSString *match=@"(^[\u4e00-\u9fa5]+$)";
            NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF matches %@", match];
            return [predicate evaluateWithObject:str];
        }

#### 三十三. 解决父视图和子视图的手势冲突问题 ####

/** 解决手势冲突 */
        - (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldReceiveTouch:(UITouch *)touch{
            if ([touch.view isDescendantOfView:cicView]) {
                return NO;
            }
            return YES;
        }

#### 三十四. 获取当前连接的Wi-Fi的名称 ####

NSString *wifiName = @"Not Found";
            CFArrayRef myArray = CNCopySupportedInterfaces();
            if (myArray != nil) {
                CFDictionaryRef myDict = CNCopyCurrentNetworkInfo(CFArrayGetValueAtIndex(myArray, 0));
                if (myDict != nil) {
                    NSDictionary *dict = (NSDictionary*)CFBridgingRelease(myDict);
                    wifiName = [dict valueForKey:@"SSID"];
                }
            }

#### 三十五. 跨控制器跳转返回 ####

for (UIViewController *controller in self.navigationController.viewControllers) { 
            if ([controller isKindOfClass:[@“你要返回的控制器类名” class]]) {
                 [self.navigationController popToViewController:controller animated:YES];
             }
         }

#### 三十六. layer.cornerRadius 圆角流畅性的优化 ####

loginBtn.layer.rasterizationScale = [UIScreen mainScreen].scale;

#### 三十七. 导航栏和下方视图间隔距离消失 ####

self.automaticallyAdjustsScrollViewInsets=YES;

#### 三十八. 毛玻璃效果(ios8.0以后的版本) ####

UIVisualEffectView *visualEffectView = [[UIVisualEffectView alloc] initWithEffect:[UIBlurEffect effectWithStyle:UIBlurEffectStyleLight]];
        visualEffectView.frame = CGRectMake(0, 0, 320*[FlexibleFrame ratio], 180*[FlexibleFrame ratio]);
        visualEffectView.alpha = 1.0;

#### 三十九. 移动工程不需要配置路径 ####

创建.pch文件时 , BuildSetting 中的 Prefix Header 中的路径开头可以写 $(SRCROOT)/工程地址, 这样写的好处可以使你的挪动代码不用手动更换路径!

#### 四十. 判断两个数组是否相同 ####

NSArray *array1 = [NSArray arrayWithObjects:@"a", @"b", @"c",  nil];
        NSArray *array2 = [NSArray arrayWithObjects:@"d", @"a", @"c",  nil];
        bool bol = false;
        //创建俩新的数组
        NSMutableArray *oldArr = [NSMutableArray arrayWithArray:array1];
        NSMutableArray *newArr = [NSMutableArray arrayWithArray:array2];
        //对数组1排序。
        [oldArr sortUsingComparator:^NSComparisonResult(id obj1, id obj2){
            return obj1 > obj2;
        }];
        //对数组2排序。
        [newArr sortUsingComparator:^NSComparisonResult(id obj1, id obj2){
            return obj1 > obj2;
        }];
        if (newArr.count == oldArr.count) {
            bol = true;
            for (int16_t i = 0; i < oldArr.count; i++) {
    
                id c1 = [oldArr objectAtIndex:i];
                id newc = [newArr objectAtIndex:i];
    
                if (![newc isEqualToString:c1]) {
                    bol = false;
                    break;
                }
            }
        }
        if (bol) {
            NSLog(@" ------------- 两个数组的内容相同！");
        }
        else {
            NSLog(@"-=-------------两个数组的内容不相同！");
        }

#### 四十一. block ####

对于block，都应该使用copy来声明，原因是block来捕获上下文的信息 [官方文档][Link 1]

#### 四十二. 使应用在后台运行 ####

- (void)applicationDidEnterBackground:(UIApplication *)application  
    {  
        __block UIBackgroundTaskIdentifier bgTask = UIBackgroundTaskInvalid;  
        bgTask = [application beginBackgroundTaskWithExpirationHandler:^{  
            dispatch_async(dispatch_get_main_queue(), ^{  
                if (bgTask != UIBackgroundTaskInvalid) {  
                    bgTask = UIBackgroundTaskInvalid;  
                }  
            });  
        }];  
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{  
            dispatch_async(dispatch_get_main_queue(), ^{  
                if (bgTask != UIBackgroundTaskInvalid) {  
                    bgTask = UIBackgroundTaskInvalid;  
                }  
            });  
        });  
    }

但其实不是应用一直在运行。

#### 四十三. 计算一段NSString在视图中渲染出来的尺寸 ####

+ (CGSize)sizeOfString:(NSString *)textString font:(UIFont *)font bound:(CGSize)bound {  
        NSMutableParagraphStyle * paragraphStyle = [[NSMutableParagraphStyle alloc] init];  
        paragraphStyle.lineBreakMode = NSLineBreakByWordWrapping;  
        paragraphStyle.alignment = NSTextAlignmentLeft;  
        if (font == nil) {  
            font = [UIFont systemFontOfSize:[UIFont systemFontSize]];  
        }  
        NSDictionary * attributes = @{NSFontAttributeName : font,  
                                      NSParagraphStyleAttributeName : paragraphStyle};  
    
        NSAttributedString* attributedString = [[NSAttributedString alloc] initWithString:textString attributes:attributes];  
        return [TTTAttributedLabel sizeThatFitsAttributedString:attributedString  
                                                withConstraints:CGSizeMake(bound.width, 999)  
                                         limitedToNumberOfLines:0];  
    }

#### 四十四. 获取相应的字体类型名 ####

for(NSString *fontfamilyname in [UIFont familyNames])  
    {  
        NSLog(@"Family:'%@'",fontfamilyname);  
        for(NSString *fontName in [UIFont fontNamesForFamilyName:fontfamilyname])  
        {  
            NSLog(@"\tfont:'%@'",fontName);  
        }  
        NSLog(@"~~~~~~~~");  
    }

#### 四十五. Masonry和SVProgreaaHUD需要注意 ####

使用Masonry约束TTTAttributedLabel的时候，初始化TTTAttributedLabel需要设置frame为CGRectZero，否则约束会不生效。
    SVProgressHUD如果要自定义一些属性，比如loading状态转圈的颜色，必须先设置style为SVProgressHUDStyleCustom，这样自定义的状态才会生效。

##待续！！

[Link 1]: https://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/WorkingwithBlocks/WorkingwithBlocks.html#//apple_ref/doc/uid/TP40011210-CH8-SW12