iOS 开发一些小技巧

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TableView不显示没内容的Cell怎么办?
很简单

self.tableView.tableFooterView = [[UIView alloc] init];
试过的都说好.

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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)self;

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ScrollView莫名其妙不能在viewController划到顶怎么办?
self.automaticallyAdjustsScrollViewInsets = NO;

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键盘事件写的好烦躁,都想摔键盘了,怎么办?
1.买个结实的键盘.
2.使用IQKeyboardManager(github上可搜索),用完之后腰也不疼了,腿也不酸了.

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为什么我的app老是不流畅,到底哪里出了问题?
这个神器叫做:KMCGeigerCounter,快去github搬运吧.

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怎么在不新建一个Cell的情况下调整separaLine的位置?
_myTableView.separatorInset = UIEdgeInsetsMake(0, screenWidth, 0, 0);

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怎么点击self.view就让键盘收起,需要添加一个tapGestures么?
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
   [self.view endEditing:YES];
}

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怎么给每个ViewController设定默认的背景图片?
使用基类啊,少年。
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想在代码里改在xib里添加的layoutAttributes,但是怎么用代码找啊?
像拉button一样的拉你的约束.nslayoutattribute也是可以拉线的.

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怎么像safari一样滑动的时候隐藏navigationbar?
navigationController.hidesBarsOnSwipe = Yes
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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];
                                                     
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CoreData用起来好烦,语法又臭又长,怎么办?
MagicRecord

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

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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;
}
}


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拉伸图片的时候怎么才能让图片不变形？
1.UIImage *image = [[UIImage imageNamed:@"xxx"] stretchableImageWithLeftCapWidth:10 topCapHeight:10];
2.使用九切片技术

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怎么播放GIF的时候这么卡，有没有好点的库？
FlipBoard出品的太适合你了： 
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怎么一句话添加上拉刷新？
使用MJRefresh 最新的已经支持gif 图和添加刷新图片了

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怎么把tableview里cell的小对勾的颜色改成别的颜色？
_mTableView.tintColor = [UIColor redColor];
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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];
}

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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;

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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];
}

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