UITextFiled don't show clearButton sometimes - ios

Question

I add a simple UITableView to my project,and every cell include a UITextField with clearButtonMode = UITextFieldViewModeAlways.
but strange issue occurs .when I reloadData,some textfield don't show clear button.
so I grab the part and build a sample and never find this issue.
I just wonder is some property has a effect to the textField.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *cellIdentifier = #"userIdentifier";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:cellIdentifier];
if (!cell) {
cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault
reuseIdentifier:cellIdentifier];
}
for (UIView *sv in cell.contentView.subviews) {
[sv removeFromSuperview];
}
UITextField *tf = [[UITextField alloc] initWithFrame:cell.bounds];
tf.text = [self.tb_data[indexPath.row];
tf.rightViewMode = UITextFieldViewModeAlways;
tf.clearButtonMode = UITextFieldViewModeAlways;
tf.tag = indexPath.row+100;
tf.delegate = self;
[[cell contentView] addSubview:tf];
return cell;
}
- (BOOL)textFieldShouldBeginEditing:(UITextField *)textField
{
if (textField.tag >= 100) {
return NO;
}
return YES;
}
- (BOOL)textFieldShouldClear:(UITextField *)textField
{
if (textField.tag >= 100) {
[self.tb_data removeObjectAtIndex:textField.tag-100];
[self.tb beginUpdates];
[self.tb deleteRowsAtIndexPaths:#[[NSIndexPath indexPathForRow:textField.tag-100 inSection:0]] withRowAnimation:UITableViewRowAnimationLeft];
[UIView animateWithDuration:0.3
animations:^{
CGRect frame = self.tb.frame;
frame.size.height = 40*self.tb_data.count;
self.tb.frame = frame;
}];
[self.tb endUpdates];
[self.tb reloadData];
}
return YES;
}