UITableView的全面解析(一) 待续中...

1 - (void)viewDidLoad {
2     [super viewDidLoad];
3     //设置控制器为数据源对象
4     self.tableView.dataSource = self;
5     //设置统一的行高
6     self.tableView.rowHeight = 70;
7 }

1 - (void)viewDidLoad {
2     [super viewDidLoad];
3     //设置控制器为数据源对象
4     self.tableView.dataSource = self;
5   
6     //预设行高
7     self.tableView.estimatedRowHeight = 300;
8 }

 1 NS_CLASS_AVAILABLE_IOS(2_0) @interface UITableView : UIScrollView <NSCoding>
 2 
 3 - (instancetype)initWithFrame:(CGRect)frame style:(UITableViewStyle)style NS_DESIGNATED_INITIALIZER; // must specify style at creation. -initWithFrame: calls this with UITableViewStylePlain
 4 - (nullable instancetype)initWithCoder:(NSCoder *)aDecoder NS_DESIGNATED_INITIALIZER;
 5 
 6 @property (nonatomic, readonly) UITableViewStyle style;
 7 @property (nonatomic, weak, nullable) id <UITableViewDataSource> dataSource;
 8 @property (nonatomic, weak, nullable) id <UITableViewDelegate> delegate;
 9 @property (nonatomic) CGFloat rowHeight;             // will return the default value if unset
10 @property (nonatomic) CGFloat sectionHeaderHeight;   // will return the default value if unset
11 @property (nonatomic) CGFloat sectionFooterHeight;   // will return the default value if unset
12 @property (nonatomic) CGFloat estimatedRowHeight NS_AVAILABLE_IOS(7_0); // default is 0, which means there is no estimate
13 @property (nonatomic) CGFloat estimatedSectionHeaderHeight NS_AVAILABLE_IOS(7_0); // default is 0, which means there is no estimate
14 @property (nonatomic) CGFloat estimatedSectionFooterHeight NS_AVAILABLE_IOS(7_0); // default is 0, which means there is no estimate
15 @property (nonatomic) UIEdgeInsets separatorInset NS_AVAILABLE_IOS(7_0) UI_APPEARANCE_SELECTOR; // allows customization of the frame of cell separators
16 
17 @property (nonatomic, strong, nullable) UIView *backgroundView NS_AVAILABLE_IOS(3_2); // the background view will be automatically resized to track the size of the table view.  this will be placed as a subview of the table view behind all cells and headers/footers.  default may be non-nil for some devices.

1 typedef NS_ENUM(NSInteger, UITableViewStyle) {
2     UITableViewStylePlain,                         // regular table view
3     UITableViewStyleGrouped     // preferences style table view
4 };

 1 NS_CLASS_AVAILABLE_IOS(2_0) @interface UITableViewCell : UIView <NSCoding, UIGestureRecognizerDelegate>
 2 
 3 // Designated initializer.  If the cell can be reused, you must pass in a reuse identifier.  You should use the same reuse identifier for all cells of the same form.  
 4 - (instancetype)initWithStyle:(UITableViewCellStyle)style reuseIdentifier:(nullable NSString *)reuseIdentifier NS_AVAILABLE_IOS(3_0) NS_DESIGNATED_INITIALIZER;
 5 - (nullable instancetype)initWithCoder:(NSCoder *)aDecoder NS_DESIGNATED_INITIALIZER;
 6 
 7 // Content.  These properties provide direct access to the internal label and image views used by the table view cell.  These should be used instead of the content properties below.
 8 @property (nonatomic, readonly, strong, nullable) UIImageView *imageView NS_AVAILABLE_IOS(3_0);   // default is nil.  image view will be created if necessary.
 9 
10 @property (nonatomic, readonly, strong, nullable) UILabel *textLabel NS_AVAILABLE_IOS(3_0);   // default is nil.  label will be created if necessary.
11 @property (nonatomic, readonly, strong, nullable) UILabel *detailTextLabel NS_AVAILABLE_IOS(3_0); // default is nil.  label will be created if necessary (and the current style supports a detail label).
12 
13 // If you want to customize cells by simply adding additional views, you should add them to the content view so they will be positioned appropriately as the cell transitions into and out of editing mode.
14 @property (nonatomic, readonly, strong) UIView *contentView;
15 
16 // Default is nil for cells in UITableViewStylePlain, and non-nil for UITableViewStyleGrouped. The ‘backgroundView‘ will be added as a subview behind all other views.
17 @property (nonatomic, strong, nullable) UIView *backgroundView;

 1 @implementation ViewController

 2 static NSString *ID = @"cell_id”;
 3 //这里要申明一下ID,也就是缓存池创建的cell的标记符 在ViewController里面申明这个ID是什么!
 4 
 5 //添加static 关键字, 这样创建的ID会转移保存到静态区,这样每次创建的ID和 常量”cell_id” 都不会被销毁,  下一次创建的时候 直接调用,不会重复创建了;
 6     //2.创建一个单元格  有三种方式:如下  推荐使用第三种;
 7     // 2.1> 先从缓存池中尝试去取一个单元格
 8     // 用来标识缓存池中的cell的id （可重用id）
 9     // static NSString *ID = @"cell_id";
10     // 根据可重用ID, 在缓存池中查找对应的cell
11 
12     //方式1 :原始方式  方式1是每移除一个,就创建一个cell,会不停的创建,性能低,总有内存爆满的时候,会崩溃
13     UITableViewCell *cell = [[UITableViewCell alloc]initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:nil];
14 
15     //方式2: 如刚好一个 页面有8个cell,一启动会创建8个,当滚动一点点的时候,第一个没有进缓存池,而第9个已经出来了,这个时候又多了一个cell,这种方式至少会创建9个,如果是ABAB型的,还会有第10个,也有点不妥,
16     UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:ID];
17     if (cell == nil) {
18         cell = [[UITableViewCell alloc]initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:ID];
19     }
20     //方式3:这种方式是最好的,如,也是ABAB类型的,到缓存池里面找和创建cell是一步搞定,底层是直接就写好了的, 但注意,这里需要在启动程序的时候注册一个cell,也就是在viewDidLoad里面,   推荐用这种!!
21     UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:ID forIndexPath:indexPath];
22       //此时,当一个cell从屏幕滚出去以后,不会销毁,而是放到了"缓存池"中;

23 #pragma mark ----viewDidLoad 设置数据源对象
24 - (void)viewDidLoad {
25     [super viewDidLoad];
26     //设置控制器为数据源对象
27     self.tableView.dataSource = self;
28     //设置统一的行高
29     self.tableView.rowHeight = 70;
30 
31     //注册一个cell
32     [self.tableView registerClass:[UITableViewCell class] forCellReuseIdentifier:ID];
33 }
34 ——>
35 这个是为方法3注册的一个cell,便于方式3调用; 要用这种方法,必须要先注册一个cell 在viewDidload 里面注册,注册就是告诉系统,我们用的ID到底是什么类型的cell,