IOS開發基礎知識--碎片40

1:Masonry快速查看報錯小技巧

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

註意:MASAttachKeys會顯示出比較明瞭的錯誤信息；

2:iOS跳轉到系統設置

註意：想要實現應用內跳轉到系統設置界面功能,需要先在Targets-Info-URL Types-URL Schemes中添加prefs

跳轉到WIFI設置
if ([[UIApplication sharedApplication] 
        canOpenURL:[NSURL URLWithString:@"prefs:root=WIFI"]])
{
        [[UIApplication sharedApplication] 
        openURL:[NSURL URLWithString:@"prefs:root=WIFI"]];
}

跳轉到藍牙
if ([[UIApplication sharedApplication] 
        canOpenURL:[NSURL URLWithString:@"prefs:root=Bluetooth"]])
{
        [[UIApplication sharedApplication] 
        openURL:[NSURL URLWithString:@"prefs:root=Bluetooth"]];
}

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

跳轉到關於本機
if ([[UIApplication sharedApplication] 
        canOpenURL:[NSURLURLWithString:
        @"prefs:root=General&path=About"]])
{
        [[UIApplication sharedApplication] 
        openURL:[NSURL URLWithString:@"prefs:
            root=General&path=About"]];
}


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


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

 3:UITableView section隨著cell滾動 

實現UITableView 的下麵這個方法，
#pragma mark - Scroll
- (void)scrollViewDidScroll:(UIScrollView *)scrollView{
    CGFloat sectionHeaderHeight = 40;
       //固定section 隨著cell滾動而滾動
    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);
        
    }

}

 4:TableView如何刷新指定的cell 或section  

//一個section刷新    

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

[tableview reloadSections:indexSet withRowAnimation:UITableViewRowAnimationAutomatic];    



//一個cell刷新    

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

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

 5:TableView另一種實現隔行空白的效果

增加總體條數，然後再求餘判斷

- (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;
}

 6:滾動TableView，滾動到指定的位置

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

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