IOS开发基础知识--碎片40

1:Masonry快速查看报错小技巧

self.statusLabel = [UILabel new];
[self.contentView addSubview:self.statusLabel];
MASAttachKeys(self.statusLabel);

[self.statusLabel mas_makeConstraints:^(MASConstraintMaker *make) {
make.top.equalTo(self.contentView).offset(15.0f);
make.left.equalTo(self.contentView).offset(.f);
make.height.equalTo();
make.bottom.equalTo(self.contentView);
}];

注意:MASAttachKeys会显示出比较明了的错误信息；

2:iOS跳转到系统设置

注意：想要实现应用内跳转到系统设置界面功能,需要先在Targets-Info-URL Types-URL Schemes中添加prefs

跳转到WIFI设置
if ([[UIApplication sharedApplication]
        canOpenURL:[NSURL URLWithString:@"prefs:root=WIFI"]])
{
        [[UIApplication sharedApplication]
        openURL:[NSURL URLWithString:@"prefs:root=WIFI"]];
}

跳转到蓝牙
if ([[UIApplication sharedApplication]
        canOpenURL:[NSURL URLWithString:@"prefs:root=Bluetooth"]])
{
        [[UIApplication sharedApplication]
        openURL:[NSURL URLWithString:@"prefs:root=Bluetooth"]];
}

跳转到通用
if ([[UIApplication sharedApplication]
        canOpenURL:[NSURL URLWithString:@"prefs:root=General"]])
{
        [[UIApplication sharedApplication]
        openURL:[NSURL URLWithString:@"prefs:root=General"]];
}

跳转到关于本机
if ([[UIApplication sharedApplication]
        canOpenURL:[NSURLURLWithString:
        @"prefs:root=General&path=About"]])
{
        [[UIApplication sharedApplication]
        openURL:[NSURL URLWithString:@"prefs:
            root=General&path=About"]];
}

跳转到定位服务
if ([[UIApplication sharedApplication]
        canOpenURL:[NSURL URLWithString:@"prefs:
        root=LOCATION_SERVICES"]])
{
        [[UIApplication sharedApplication]
        openURL:[NSURL URLWithString:@"prefs:
        root=LOCATION_SERVICES"]];
}

跳转到通知
if ([[UIApplication sharedApplication]
        canOpenURL:[NSURL URLWithString:@"prefs:
        root=NOTIFICATIONS_ID"]])
{
      [[UIApplication sharedApplication]
      openURL:[NSURL URLWithString:@"prefs:
      root=NOTIFICATIONS_ID"]];
}

 3:UITableView section随着cell滚动 

实现UITableView 的下面这个方法，
#pragma mark - Scroll
- (void)scrollViewDidScroll:(UIScrollView *)scrollView{
    CGFloat sectionHeaderHeight = ;
       //固定section 随着cell滚动而滚动
    if (scrollView.contentOffset.y<=sectionHeaderHeight&&scrollView.contentOffset.y>=) {

        scrollView.contentInset = UIEdgeInsetsMake(-scrollView.contentOffset.y, , , );

    } else if (scrollView.contentOffset.y>=sectionHeaderHeight) {

        scrollView.contentInset = UIEdgeInsetsMake(-sectionHeaderHeight, , , );

    }

}

4:TableView如何刷新指定的cell 或section  

//一个section刷新    

NSIndexSet *indexSet=[[NSIndexSet alloc]initWithIndex:];    

[tableview reloadSections:indexSet withRowAnimation:UITableViewRowAnimationAutomatic];    

//一个cell刷新    

NSIndexPath *indexPath=[NSIndexPath indexPathForRow: inSection:];    

[tableView reloadRowsAtIndexPaths:[NSArray arrayWithObjects:indexPath,nil] withRowAnimation:UITableViewRowAnimationNone];  

 5:TableView另一种实现隔行空白的效果

增加总体条数，然后再求余判断

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{

    static NSString *CELL_ID2 = @"SOME_STUPID_ID2";
    // even rows will be invisible
    if (indexPath.row %  == )
    {
        UITableViewCell * cell2 = [tableView dequeueReusableCellWithIdentifier:CELL_ID2];

        if (cell2 == nil)
        {
            cell2 = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault
                                          reuseIdentifier:CELL_ID2];
            [cell2.contentView setAlpha:];
            [cell2 setUserInteractionEnabled:NO]; // prevent selection and other stuff
        }
        return cell2;
    }

    [ccTableView setBackgroundColor:[UIColor clearColor]];
    cardsCell *cell = [tableView dequeueReusableCellWithIdentifier:@"cardsCell"];

    if(cell == nil){
      NSArray *topLevelObjects = [[NSBundle mainBundle] loadNibNamed:@"cardsCell" owner:self options:nil];
      cell = [topLevelObjects objectAtIndex:];
    }

     // Use indexPath.row/2 instead of indexPath.row for the visible section to get the correct datasource index (number of rows is increased to add the invisible rows)
        NSString *nmCard = [[self.cards valueForKeyPath:@"cards.name"] objectAtIndex:(indexPath.row/)];
        cell.descCardLabel.text = nmCard;

      return cell;
    }

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section{

    // two times minus one (invisible at even rows => visibleCount == invisibleCount+1)
    return [[self.cards valueForKeyPath:@"cards"] count] *  - ;
}

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
    if (indexPath.row %  == )
        return ;
    return ;
}

 6:滚动TableView，滚动到指定的位置

- (void)scrollToRowAtIndexPath:(NSIndexPath *)indexPath atScrollPosition:(UITableViewScrollPosition)scrollPosition animated:(BOOL)animated

typedef enum {
    UITableViewScrollPositionNone,
    UITableViewScrollPositionTop,
    UITableViewScrollPositionMiddle,
    UITableViewScrollPositionBottom
 } UITableViewScrollPosition;

 7:iOS-检测UI主线程小工具

在iOS开发中需要保证所有UI操作一定是在主线程进行，通过 hook UIView的-setNeedsLayout，-setNeedsDisplay，-setNeedsDisplayInRect三个方法，确保它们都是在主线程执行。

#import "UIView+NBUIKitMainThreadGuard.h"
#import <objc/runtime.h>

static inline void swizzling_exchangeMethod(Class clazz ,SEL originalSelector, SEL swizzledSelector){
    Method originalMethod = class_getInstanceMethod(clazz, originalSelector);
    Method swizzledMethod = class_getInstanceMethod(clazz, swizzledSelector);

    BOOL success = class_addMethod(clazz, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));
    if (success) {
        class_replaceMethod(clazz, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod));
    } else {
        method_exchangeImplementations(originalMethod, swizzledMethod);
    }
}

@implementation UIView (NBUIKitMainThreadGuard)

+(void)load
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{

        SEL needsLayoutOriginalSelector = @selector(setNeedsLayout);
        SEL needsLayoutSwizzleSelector  = @selector(guard_setNeedsLayout);
        swizzling_exchangeMethod(self, needsLayoutOriginalSelector,needsLayoutSwizzleSelector);

        SEL needsDisplaOriginalSelector = @selector(setNeedsDisplay);
        SEL needsDisplaSwizzleSelector  = @selector(guard_setNeedsDisplay);
        swizzling_exchangeMethod(self, needsDisplaOriginalSelector,needsDisplaSwizzleSelector);

        SEL needsDisplayInRectOriginalSelector = @selector(setNeedsDisplayInRect:);
        SEL needsDisplayInRectSwizzleSelector  = @selector(guard_setNeedsDisplayInRect:);
        swizzling_exchangeMethod(self, needsDisplayInRectOriginalSelector,needsDisplayInRectSwizzleSelector);

    });
}

- (void)guard_setNeedsLayout
{
    [self UIMainThreadCheck];
    [self guard_setNeedsLayout];
}

- (void)guard_setNeedsDisplay
{
    [self UIMainThreadCheck];
    [self guard_setNeedsDisplay];
}

- (void)guard_setNeedsDisplayInRect:(CGRect)rect
{
    [self UIMainThreadCheck];
    [self guard_setNeedsDisplayInRect:rect];
}

- (void)UIMainThreadCheck
{
    NSString *desc = [NSString stringWithFormat:@"%@", self.class];
    NSAssert([NSThread isMainThread], desc);
}

@end