UITableView 加载时候，代理方法执行顺序

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView

{

NSLog(@"numberOfSectionsInTableView");

return 1;

}

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

{

NSLog(@"numberOfRowsInSection");

return 3;

}

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

{

static NSString *cellIdentifier=@"cell";

UITableViewCell *cell=[tableView dequeueReusableCellWithIdentifier:cellIdentifier];

if (cell==nil) {

cell=[[UITableViewCell alloc]initWithStyle:UITableViewCellStyleDefault reuseIdentifier:cellIdentifier];

NSLog(@"cellForRowAtIndexPath");

}

NSLog(@"cellForRowAtIndexPath01");

return cell;

}

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath

{

NSLog(@"heightForRowAtIndexPath");

return 40;

}

初次加载视图，执行顺序

2017-06-14 22:42:43.095 oc1[6631:246491] numberOfSectionsInTableView

2017-06-14 22:42:43.095 oc1[6631:246491] numberOfRowsInSection

2017-06-14 22:42:43.096 oc1[6631:246491] heightForRowAtIndexPath

2017-06-14 22:42:43.426 oc1[6631:246491] numberOfSectionsInTableView

2017-06-14 22:42:43.426 oc1[6631:246491] numberOfRowsInSection

2017-06-14 22:42:43.427 oc1[6631:246491] heightForRowAtIndexPath

2017-06-14 22:42:43.434 oc1[6631:246491] numberOfSectionsInTableView

2017-06-14 22:42:43.435 oc1[6631:246491] numberOfRowsInSection

2017-06-14 22:42:43.435 oc1[6631:246491] heightForRowAtIndexPath

2017-06-14 22:42:43.437 oc1[6631:246491] cellForRowAtIndexPath

2017-06-14 22:42:43.437 oc1[6631:246491] cellForRowAtIndexPath01

2017-06-14 22:42:43.438 oc1[6631:246491] heightForRowAtIndexPath

2017-06-14 22:42:43.445 oc1[6631:246491] cellForRowAtIndexPath

2017-06-14 22:42:43.445 oc1[6631:246491] cellForRowAtIndexPath01

2017-06-14 22:42:43.446 oc1[6631:246491] heightForRowAtIndexPath

2017-06-14 22:42:43.447 oc1[6631:246491] cellForRowAtIndexPath

2017-06-14 22:42:43.447 oc1[6631:246491] cellForRowAtIndexPath01

2017-06-14 22:42:43.447 oc1[6631:246491] heightForRowAtIndexPath

滑动cell 时候，执行顺序

2017-06-14 22:45:16.497 oc1[6631:246491] cellForRowAtIndexPath01

2017-06-14 22:45:16.498 oc1[6631:246491] heightForRowAtIndexPath

2017-06-14 22:45:16.580 oc1[6631:246491] cellForRowAtIndexPath01

2017-06-14 22:45:16.581 oc1[6631:246491] heightForRowAtIndexPath

2017-06-14 22:45:16.664 oc1[6631:246491] cellForRowAtIndexPath01

2017-06-14 22:45:16.665 oc1[6631:246491] heightForRowAtIndexPath

观察可见，初次加载时候先调用heightForRowAtIndexPath方法给默认cell 一个高度，当创建cell 时候，调用了cellForRowAtIndexPath之后又调用了heightForRowAtIndexPath 重新设置了一下高度。当我们在屏幕中滑动cell时候，重用已经存在的cell，不再创建新cell，并且是先调用了cellForRowAtIndexPath01 然后再调用heightForRowAtIndexPath 方法，给cell重新设置高度。