iOS开发基础知识--碎片40

iOS开发基础知识--碎片40

[b]iOS开发基础知识--碎片40[/b]

[b]1:Masonry快速查看报错小技巧[/b]

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(10.f);
make.height.equalTo(10);
make.bottom.equalTo(self.contentView);
}];

注意:MASAttachKeys会显示出比较明了的错误信息；

[b]2:iOS跳转到系统设置[/b]

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"]];
}

[b] 3:UITableView section随着cell滚动 [/b]

实现UITableView 的下面这个方法，
#pragma mark - Scroll
- (void)scrollViewDidScroll:(UIScrollView *)scrollView{
CGFloat sectionHeaderHeight = 40;
//固定section 随着cell滚动而滚动
if (scrollView.contentOffset.y<=sectionHeaderHeight&&scrollView.contentOffset.y>=0) {

scrollView.contentInset = UIEdgeInsetsMake(-scrollView.contentOffset.y, 0, 0, 0);

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

scrollView.contentInset = UIEdgeInsetsMake(-sectionHeaderHeight, 0, 0, 0);

}

}

[b]4:TableView如何刷新指定的cell 或section [/b]

//一个section刷新

NSIndexSet *indexSet=[[NSIndexSet alloc]initWithIndex:2];

[tableview reloadSections:indexSet withRowAnimation:UITableViewRowAnimationAutomatic];

//一个cell刷新

NSIndexPath *indexPath=[NSIndexPath indexPathForRow:3 inSection:0];

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

[b] 5:TableView另一种实现隔行空白的效果[/b]

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 % 2 == 1)
{
UITableViewCell * cell2 = [tableView dequeueReusableCellWithIdentifier:CELL_ID2];

if (cell2 == nil)
{
cell2 = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault
reuseIdentifier:CELL_ID2];
[cell2.contentView setAlpha:0];
[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:0];
}

// 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/2)];
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] * 2 - 1;
}

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
if (indexPath.row % 2 == 1)
return 40;
return 162;
}

[b] 6:滚动TableView，滚动到指定的位置[/b]

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

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

[b] 7:iOS-检测UI主线程小工具[/b]

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