iOS版 - 的cellForRowAtIndexPath代码说明

Question

这里是整个代码：

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

{ 
    static NSString *CellIdentifier = @"DetailCell"; 
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; 

    if (cell == nil) 
    cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleValue2 
            reuseIdentifier:CellIdentifier]; 

    NSUInteger sectionIndex = [indexPath section]; 
    NSUInteger rowIndex = [indexPath row]; 

    NSDictionary *section = [self.sections objectAtIndex:sectionIndex]; 
    NSArray *rows = [section objectForKey:@"rows"]; 
    NSDictionary *row = [rows objectAtIndex:rowIndex]; 
    cell.textLabel.text = [row objectForKey:@"label"]; 
    cell.detailTextLabel.text = [[self.myManagedObject valueForKey:[row objectForKey:@"key"]] description]; 
    return cell; 
} 

我的问题是关于：

cell.textLabel.text = [row objectForKey:@"label"]; 
cell.detailTextLabel.text = [[self.myManagedObject valueForKey:[row objectForKey:@"key"]] description]; //This is NSDate 

1. 为什么采用两种不同的格式的代码：objectForKey & valueForKey？
2. 为什么没有必要使用objectForKey调用self.myManagedObject？
3. 描述的目的是什么？

Answer 1

为什么在用两种不同的格式的代码：objectForKey & valueForKey？

为什么不需要调用self.myManagedObject与 objectForKey？

self.myManagedObject是NSManagedObject。 NSManagedObject没有objectForKey:方法。

row是NSDictionary类型。 objectForKey:是一种字典方法。

描述的目的是什么？

[self.myManagedObject valueForKey:[row objectForKey:@"key"]]应当返回一个对象，该对象将包含一个NSString类型属性作为description。

他们只是一条线。您可以将其拆分为多行如下

YourCustomClass *customclassObj = [self.myManagedObject valueForKey:[row objectForKey:@"key"]]; 

cell.detailTextLabel.text = customclassObj.description; 

Answer 2

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath; 
{ 
    static NSString *CellIdentifier = @"Cell"; 

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; 
    if (cell == nil) 
    { 
     //create new cell 
     cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease]; 
    } 



    [tableView setRowHeight: 50.00]; 

    UILabel *name=[[UILabel alloc]initWithFrame:CGRectMake(10, 5, 70, 30)]; 
    name.text=@"Ajay"; 
    [cell.contentView addSubview:name]; 
    [name release]; 

    // cell.selectionStyle = UITableViewCellSelectionStyleNone; 
    //cell.contentView.backgroundColor=[UIColor whiteColor]; 
    UIButton *btn1=[[UIButton alloc]initWithFrame:CGRectMake(80, 5, 70, 30)]; 
    //UIButton *btn1=[UIButton buttonWithType:UIButtonTypeRoundedRect]; 
    //btn1.frame=CGRectMake(80, 5, 40, 30); 
    [btn1 setTitle:@"Name" forState:UIControlStateNormal]; 
    [btn1 setTitleColor:[UIColor blackColor] forState:UIControlStateNormal]; 
    //[btn1 addTarget:self action:@selector(Nam:) forControlEvents:UIControlEventTouchUpInside]; 
    btn1.backgroundColor=[UIColor greenColor]; 
    [[btn1 layer]setCornerRadius:8.0f]; 
    [[btn1 layer]setBorderWidth:1.0f]; 
    [cell.contentView addSubview:btn1]; 
    [btn1 release]; 

    UILabel *add=[[UILabel alloc]initWithFrame:CGRectMake(10, 56, 70, 50)]; 
    add.text=@"Biliya"; 
    [cell.contentView addSubview:add]; 
    [add release]; 

    // cell.selectionStyle = UITableViewCellSelectionStyleNone; 
    //cell.contentView.backgroundColor=[UIColor whiteColor]; 
    UIButton *btn2=[[UIButton alloc]initWithFrame:CGRectMake(80, 56, 70, 30)]; 
    //UIButton *btn1=[UIButton buttonWithType:UIButtonTypeRoundedRect]; 
    //btn1.frame=CGRectMake(80, 5, 40, 30); 
    [btn2 setTitle:@"Address" forState:UIControlStateNormal]; 
    [btn2 setTitleColor:[UIColor blackColor] forState:UIControlStateNormal]; 
    //[btn1 addTarget:self action:@selector(Nam:) forControlEvents:UIControlEventTouchUpInside]; 
    btn2.backgroundColor=[UIColor greenColor]; 
    [[btn2 layer]setCornerRadius:8.0f]; 
    [[btn2 layer]setBorderWidth:1.0f]; 
    [cell.contentView addSubview:btn2]; 
    [btn2 release]; 




    return cell; 

}