iOS开发常见问题解决方案（二）

10、查看系统所有字体

// 打印字体
for (id familyName in [UIFont familyNames]) {
    NSLog(@"%@", familyName);
    for (id fontName in [UIFont fontNamesForFamilyName:familyName]) NSLog(@"  %@", fontName);
}
// 也可以进入这个网址查看 http://iosfonts.com/

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11、获取随机数

NSInteger i = arc4random();

12、获取随机数小数(0-1之间)

#define ARC4RANDOM_MAX      0x100000000
double val = ((double)arc4random() / ARC4RANDOM_MAX);

13、AVPlayer视频播放完成的通知监听

[[NSNotificationCenter defaultCenter] 
      addObserver:self
      selector:@selector(videoPlayEnd)
      name:AVPlayerItemDidPlayToEndTimeNotification 
      object:nil];

14、判断两个rect是否有交叉

 if (CGRectIntersectsRect(rect1, rect2)) {
}

15、判断一个字符串是否为数字

NSCharacterSet *notDigits = [[NSCharacterSet decimalDigitCharacterSet] invertedSet];
    if ([str rangeOfCharacterFromSet:notDigits].location == NSNotFound)
    {
      // 是数字
    } else
    {
      // 不是数字
    }

16、将一个view保存为pdf格式

- (void)createPDFfromUIView:(UIView*)aView saveToDocumentsWithFileName:(NSString*)aFilename
{
    NSMutableData *pdfData = [NSMutableData data];
    UIGraphicsBeginPDFContextToData(pdfData, aView.bounds, nil);
    UIGraphicsBeginPDFPage();
    CGContextRef pdfContext = UIGraphicsGetCurrentContext();
    [aView.layer renderInContext:pdfContext];
    UIGraphicsEndPDFContext();

    NSArray* documentDirectories = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask,YES);
    NSString* documentDirectory = [documentDirectories objectAtIndex:0];
    NSString* documentDirectoryFilename = [documentDirectory stringByAppendingPathComponent:aFilename];
    [pdfData writeToFile:documentDirectoryFilename atomically:YES];
    NSLog(@"documentDirectoryFileName: %@",documentDirectoryFilename);
}

17、让一个view在父视图中心

child.center = [parent convertPoint:parent.center fromView:parent.superview];

18、获取当前导航控制器下前一个控制器

- (UIViewController *)backViewController
{
    NSInteger myIndex = [self.navigationController.viewControllers indexOfObject:self];

    if ( myIndex != 0 && myIndex != NSNotFound ) {
        return [self.navigationController.viewControllers objectAtIndex:myIndex-1];
    } else {
        return nil;
    }
}

19、保存UIImage到本地

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *filePath = [[paths objectAtIndex:0] stringByAppendingPathComponent:@"Image.png"];

[UIImagePNGRepresentation(image) writeToFile:filePath atomically:YES];

20、键盘上方增加工具栏

UIToolbar *keyboardDoneButtonView = [[UIToolbar alloc] init];
[keyboardDoneButtonView sizeToFit];
UIBarButtonItem *doneButton = [[UIBarButtonItem alloc] initWithTitle:@"Done"
                                                               style:UIBarButtonItemStyleBordered target:self
                                                              action:@selector(doneClicked:)];
[keyboardDoneButtonView setItems:[NSArray arrayWithObjects:doneButton, nil]];
txtField.inputAccessoryView = keyboardDoneButtonView;

21、copy一个view

因为UIView没有实现copy协议，因此找不到copyWithZone方法，使用copy的时候导致崩溃

但是我们可以通过归档再解档实现copy，这相当于对视图进行了一次深拷贝，代码如下

id copyOfView = 
[NSKeyedUnarchiver unarchiveObjectWithData:[NSKeyedArchiver archivedDataWithRootObject:originalView]];

22、在image上绘制文字并生成新的image

    UIGraphicsBeginImageContext(image.size);
    [image drawInRect:CGRectMake(0,0,image.size.width,image.size.height)];
    CGRect rect = CGRectMake(point.x, point.y, image.size.width, image.size.height);
    [[UIColor whiteColor] set];
    [text drawInRect:CGRectIntegral(rect) withFont:font]; 
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

23、判断一个view是否为另一个view的子视图

// 如果myView是self.view本身，也会返回yes
BOOL isSubView = [myView isDescendantOfView:self.view];

24、判断一个字符串是否包含另一个字符串

// 方法一、这种方法只适用于iOS8之后，如果是配iOS8之前用方法二
if ([str containsString:otherStr]) NSLog(@"包含");

// 方法二
NSRange range = [str rangeOfString:otherStr];
if (range.location != NSNotFound) NSLog(@"包含");

25、UICollectionView自动滚动到某行

// 重写viewDidLayoutSubviews方法
-(void)viewDidLayoutSubviews {
   [super viewDidLayoutSubviews];
   [self.collectionView scrollToItemAtIndexPath:indexPath atScrollPosition:
UICollectionViewScrollPositionCenteredVertically animated:NO];
}

26、修改系统UIAlertController

// 但是据说这种方法会被App Store拒绝(慎用！)
UIAlertController *alertVC = [UIAlertController alertControllerWithTitle:
@"" message:@"" preferredStyle:UIAlertControllerStyleActionSheet];
    NSMutableAttributedString *hogan =
 [[NSMutableAttributedString alloc] initWithString:@"我是一个大文本"];
    [hogan addAttribute:NSFontAttributeName
                  value:[UIFont systemFontOfSize:30]
                  range:NSMakeRange(4, 1)];
    [hogan addAttribute:NSForegroundColorAttributeName
                  value:[UIColor redColor]
                  range:NSMakeRange(4, 1)];
    [alertVC setValue:hogan forKey:@"attributedTitle"];

    UIAlertAction *button = [UIAlertAction actionWithTitle:
@"Label text" style:UIAlertActionStyleDefault handler:^(UIAlertAction *action){ }];
    UIImage *accessoryImage = [UIImage imageNamed:@"1"];
    [button setValue:accessoryImage forKey:@"image"];
    [alertVC addAction:button];
    [self presentViewController:alertVC animated:YES completion:nil];

27、判断某一行的cell是否已经显示

CGRect cellRect = [tableView rectForRowAtIndexPath:indexPath];
BOOL completelyVisible = CGRectContainsRect(tableView.bounds, cellRect);

28、让导航控制器pop回指定的控制器

NSMutableArray *allViewControllers = [NSMutableArray arrayWithArray:[self.navigationController viewControllers]];
for (UIViewController *aViewController in allViewControllers) {
    if ([aViewController isKindOfClass:[RequiredViewController class]]) {
        [self.navigationController popToViewController:aViewController animated:NO];
    }
}

29、动画修改label上的文字

// 方法一
CATransition *animation = [CATransition animation];
    animation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
    animation.type = kCATransitionFade;
    animation.duration = 0.75;
    [self.label.layer addAnimation:animation forKey:@"kCATransitionFade"];
    self.label.text = @"New";

// 方法二
[UIView transitionWithView:self.label
                      duration:0.25f
                       options:UIViewAnimationOptionTransitionCrossDissolve
                    animations:^{
                        self.label.text = @"Well done!";
                    } completion:nil];

// 方法三
[UIView animateWithDuration:1.0
                     animations:^{
                         self.label.alpha = 0.0f;
                         self.label.text = @"newText";
                         self.label.alpha = 1.0f;
                     }];

30、判断字典中是否包含某个key值

if ([dic objectForKey:@"yourKey"]) {
    NSLog(@"有这个值");
} else {
    NSLog(@"没有这个值");
}