iOS开发的21个技巧

开发的21个奇葩技巧

• TableView不显示没内容的Cell怎么办？
  我不想让下面的那些空显示。很简单，添加“self.tableView.tableFooterView = [[UIView alloc] init];”试过都说好，
• 自定义了leftBarbuttonItem左滑返回手势失效了怎么办？

self.navigationItem.leftBarButtonItem = [[UIBarButtonItem alloc]initWithImage:img
              style:UIBarButtonItemStylePlain
              target:self
            action:@selector(onBack:)];
self.navigationController.interactivePopGestureRecognizer.delegate = (id<UI)

• ScrollView莫名其妙不能在viewController划到顶怎么办？

self.automaticallyAdjustsScrollViewInsets = NO;

• 键盘事件写得好烦躁，都想摔键盘了怎么办？

使用IQKeyboardManager（GitHub上可搜索）

• 为什么我的App老是不流畅，到底哪里出了问题？

KMCGeigerCounter ，快去GitHub上搬运吧

• 怎么在不新建一个Cell的情况下调整separaLine的位置？

_myTableView.separatorInset = UIEdgeInsetsMake(0, 100, 0, 0);

• 怎么点击self.view就让键盘收起，需要添加一个tapGestures么？

[self.view endEditing:YES];

• 怎么给每个ViewController设定默认的背景图片？

使用基类啊

• 想在代码里改在xib里添加的layoutAttributes，但该怎么用代码找？

像拉Button一样地拉你的约束，nslayoutattribute也是可以拉线的。

• 怎么像Safari一样滑动的时候隐藏navigationbar？

navigationController.hidesBarsOnSwipe = Yes

• 导航条返回键带的title太讨厌了，怎么让它消失？

[[UIBarButtonItem appearance] setBackButtonTitlePositionAdjustment:UIOffsetMake(0, -60)                                                    forBarMetrics:UIBarMetricsDefault];

• CoreData用起来好烦，语法又臭又长怎么办？

MagicRecord

• CollectionView怎么实现tableview那种悬停的header？

CSStickyHeaderFlowLayout

• 能不能只用一个pan手势来代替UISwipegesture的各个方向？

(void)pan:(UIPanGestureRecognizer *)sender
 {
 typedef NS_ENUM(NSUInteger, UIPanGestureRecognizerDirection) {
    UIPanGestureRecognizerDirectionUndefined,
    UIPanGestureRecognizerDirectionUp,
    UIPanGestureRecognizerDirectionDown,
    UIPanGestureRecognizerDirectionLeft,
    UIPanGestureRecognizerDirectionRight
};
 static UIPanGestureRecognizerDirection direction = UIPanGestureRecognizerDirectionUndefined;
switch (sender.state) {
     case UIGestureRecognizerStateBegan: {
        if (direction == UIPanGestureRecognizerDirectionUndefined) {
             CGPoint velocity = [sender velocityInView:recognizer.view];
             BOOL isVerticalGesture = fabs(velocity.y) > fabs(velocity.x);
             if (isVerticalGesture) {
                if (velocity.y > 0) {
                    direction = UIPanGestureRecognizerDirectionDown;
                } else {
                    direction = UIPanGestureRecognizerDirectionUp;
                }
            }
             else {
                 if (velocity.x > 0) {
                    direction = UIPanGestureRecognizerDirectionRight;
                 } else {
                     direction = UIPanGestureRecognizerDirectionLeft;
                 }
             }
         }
         break;
     }
     case UIGestureRecognizerStateChanged: {
         switch (direction) {
             case UIPanGestureRecognizerDirectionUp: {
                 [self handleUpwardsGesture:sender];
                 break;
             }
             case UIPanGestureRecognizerDirectionDown: {
                 [self handleDownwardsGesture:sender];
                 break;
             }
             case UIPanGestureRecognizerDirectionLeft: {
                 [self handleLeftGesture:sender];
                 break;
             }
             case UIPanGestureRecognizerDirectionRight: {
                 [self handleRightGesture:sender];
                 break;
             }
            default: {
                 break;
             }
         }
         break;
     }
     case UIGestureRecognizerStateEnded: {
         direction = UIPanGestureRecognizerDirectionUndefined;
         break;
     }
     default:
         break;
 }
 }

• 拉伸图片的时候怎么才能让图片不变形？

UIImage *image = [[UIImage imageNamed:@"xxx"] stretchableImageWithLeftCapWidth:10 topCapHeight:10];

注：有开发者提醒这个已经弃用，现在的方法叫

resizableImageWithCapInsets。

• 怎么播放GIF的时候这么卡，有没有好点的库？

FlipBoard出品的FLAnimatedImage太适合你了。

• 怎么一句话添加上拉刷新？
  使用SVPullToRefresh库：

 [tableView addPullToRefreshWithActionHandler:^{
// prepend data to dataSource, insert cells at top of table view
// call [tableView.pullToRefreshView stopAnimating] when done
 } position:SVPullToRefreshPositionBottom];

• 怎么把tableview里Cell的小对勾颜色改成别的颜色？

_mTableView.tintColor = [UIColor redColor];

• 本来我的statusbar是lightcontent的，结果用UIImagePickerController会导致我的statusbar的样式变成黑色，怎么办？

 (void)navigationController:(UINavigationController *)navigationController willShowViewController:(UIViewController *)viewController animated:(BOOL)animated
{    [[UIApplication sharedApplication] setStatusBarStyle:UIStatusBarStyleLightContent];
}

• 怎么把我的navigationbar弄成透明的而不是带模糊的效果？

[self.navigationBar setBackgroundImage:[UIImage new]
                          forBarMetrics:UIBarMetricsDefault];
 self.navigationBar.shadowImage = [UIImage new];
 self.navigationBar.translucent = YES;
```
- 怎么改变uitextfield placeholder的颜色和位置？
继承uitextfield，重写这个方法：  
```
 (void) drawPlaceholderInRect:(CGRect)rect {
     [[UIColor blueColor] setFill];
     [self.placeholder drawInRect:rect withFont:self.font lineBreakMode:UILineBreakModeTailTruncation alignment:self.textAlignment];
 }
  ```