When did UITableViewCell done layout subview? - ios

Question

As shown in the following image, I want to add a tip(subview of the biggest UIView) that left align with the UIStackView in UITableViewCell. The width of UIStackView in UITableViewCell is dynamic, so I need to place the tip view after the UITableViewCell layout its subviews.
I've tried to add the tip view in willDisplayCell function, but the position I get there is not the final position.
Also, I tried to set the tip view's position in the UITableViewCell's layoutSubviews function. Since this function is called multiple times, the tip will go to the expected place eventually, but it will flicker at the beginning.
So in which function should I add the tip view?
--------Edited--------
Add a code snippet to make it clearer. I just want to know where should I put the following code, so that rect.origin.x is the final position of the stackview.
UIView *view = self.view;
CGRect rect = [cell.stackView convertRect:cell.stackView.bounds toView:view];
[self.tipView.leadingAnchor constraintEqualToAnchor:view.leadingAnchor constant:rect.origin.x].active = YES;
[self.tipView.trailingAnchor constraintLessThanOrEqualToAnchor:view.trailingAnchor constant:-marginConstant].active = YES;
[self.tipView.bottomAnchor constraintEqualToAnchor:self.tableView.bottomAnchor constant:-TSkBubbleClickAreaHeight-marginConstant].active = YES;
[view layoutIfNeeded];

Answer 1

Edit
To try and directly answer your question, you know when the layout of the content of the cell is completely finished when whatever you're doing to the cell is done. So, to know exactly when your cell's Stack View has been laid-out, you could subclass the stack view and implement layoutSubviews in that subclass.
Since it's still not clear exactly what you're doing, I'll offer a couple approaches...
If you are calling reloadData on the table view, you could try this:
[tableView reloadData];
dispatch_async(dispatch_get_main_queue(), ^{
[self showTipView:pth];
});
If you are calling insertRowsAtIndexPaths, you could try this:
[CATransaction begin];
[CATransaction setCompletionBlock:^{
[self showTipView:pth];
}];
[self->tableView insertRowsAtIndexPaths:#[pth] withRowAnimation:UITableViewRowAnimationRight];
[CATransaction commit];
Here's an example (I've tried to keep it simple, and provide clear comments):
ExampleTableViewCell.h
//
// ExampleTableViewCell.h
// Created by Don Mag on 9/15/20.
//
#import <UIKit/UIKit.h>
NS_ASSUME_NONNULL_BEGIN
#interface ExampleTableViewCell : UITableViewCell
- (void) configureCell:(NSString *)s;
- (UIStackView *)getStackRef;
#end
NS_ASSUME_NONNULL_END
ExampleTableViewCell.m
//
// ExampleTableViewCell.m
// Created by Don Mag on 9/15/20.
//
#import "ExampleTableViewCell.h"
#interface ExampleTableViewCell ()
{
UIStackView *stackView;
UILabel *label;
}
#end
#implementation ExampleTableViewCell
- (instancetype)initWithStyle:(UITableViewCellStyle)style reuseIdentifier:(NSString *)reuseIdentifier {
self = [super initWithStyle:style reuseIdentifier:reuseIdentifier];
if (self) {
[self commonInit];
}
return self;
}
- (void) commonInit {
label = [UILabel new];
label.backgroundColor = [UIColor yellowColor];
stackView = [UIStackView new];
stackView.translatesAutoresizingMaskIntoConstraints = NO;
[stackView addArrangedSubview:label];
[self.contentView addSubview:stackView];
UILayoutGuide *g = self.contentView.layoutMarginsGuide;
[NSLayoutConstraint activateConstraints:#[
// constrain stack view Top: 0 / Trailing: 0 / Bottom: 0
[stackView.topAnchor constraintEqualToAnchor:g.topAnchor constant:0.0],
[stackView.trailingAnchor constraintEqualToAnchor:g.trailingAnchor constant:0.0],
[stackView.bottomAnchor constraintEqualToAnchor:g.bottomAnchor constant:0.0],
]];
}
- (void) configureCell:(NSString *)s {
label.text = s;
}
- (UIStackView *)getStackRef {
return stackView;
}
#end
ExampleViewController.h
//
// ExampleViewController.h
// Created by Don Mag on 9/15/20.
//
#import <UIKit/UIKit.h>
NS_ASSUME_NONNULL_BEGIN
#interface ExampleViewController : UIViewController
#end
NS_ASSUME_NONNULL_END
ExampleViewController.m
//
// ExampleViewController.m
// Created by Don Mag on 9/15/20.
//
#import "ExampleViewController.h"
#import "ExampleTableViewCell.h"
#interface ExampleViewController () <UITableViewDataSource, UITableViewDelegate, UIScrollViewDelegate>
{
NSMutableArray *myData;
NSMutableArray *sampleStrings;
UIView *tipView;
UIButton *reloadButton;
UIButton *insertButton;
UITableView *tableView;
NSInteger idx;
NSInteger insertRow;
}
#end
#implementation ExampleViewController
- (void)viewDidLoad {
[super viewDidLoad];
// row number to insert and show the tipView
insertRow = 7;
// init some sample data
myData = [NSMutableArray new];
for (int i = 0; i < 30; i++) {
NSString *s = [NSString stringWithFormat:#"Row %i", i];
[myData addObject:s];
}
// a few example strings
sampleStrings = [NSMutableArray new];
[sampleStrings addObject:#"Short text example."];
[sampleStrings addObject:#"A little more text example."];
[sampleStrings addObject:#"Considerably longer text for this example."];
// index for sampleStrings array
idx = -1;
// create a "tip view"
// red background view with
// green background label
// label is inset 4-pts on each side
tipView = [UIView new];
tipView.backgroundColor = [UIColor redColor];
UILabel *tipLabel = [UILabel new];
tipLabel.backgroundColor = [UIColor greenColor];
tipLabel.text = #"This is the tip!";
tipView.translatesAutoresizingMaskIntoConstraints = NO;
tipLabel.translatesAutoresizingMaskIntoConstraints = NO;
[tipView addSubview:tipLabel];
[NSLayoutConstraint activateConstraints:#[
[tipLabel.topAnchor constraintEqualToAnchor:tipView.topAnchor constant:4.0],
[tipLabel.leadingAnchor constraintEqualToAnchor:tipView.leadingAnchor constant:4.0],
[tipLabel.bottomAnchor constraintEqualToAnchor:tipView.bottomAnchor constant:-4.0],
[tipLabel.trailingAnchor constraintEqualToAnchor:tipView.trailingAnchor constant:-4.0],
]];
// init buttons
reloadButton = [UIButton new];
[reloadButton setTitle:#"Reload" forState:UIControlStateNormal];
[reloadButton setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal];
[reloadButton setTitleColor:[UIColor grayColor] forState:UIControlStateHighlighted];
[reloadButton setBackgroundColor:[UIColor blueColor]];
insertButton = [UIButton new];
[insertButton setTitle:#"Insert" forState:UIControlStateNormal];
[insertButton setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal];
[insertButton setTitleColor:[UIColor grayColor] forState:UIControlStateHighlighted];
[insertButton setBackgroundColor:[UIColor blueColor]];
// init table view
tableView = [UITableView new];
for (UIView *v in #[reloadButton, insertButton, tableView]) {
v.translatesAutoresizingMaskIntoConstraints = NO;
[self.view addSubview:v];
}
UILayoutGuide *g = self.view.safeAreaLayoutGuide;
[NSLayoutConstraint activateConstraints:#[
// buttons at top
[reloadButton.topAnchor constraintEqualToAnchor:g.topAnchor constant:20.0],
[reloadButton.leadingAnchor constraintEqualToAnchor:g.leadingAnchor constant:24.0],
[insertButton.topAnchor constraintEqualToAnchor:g.topAnchor constant:20.0],
[insertButton.trailingAnchor constraintEqualToAnchor:g.trailingAnchor constant:-24.0],
[insertButton.leadingAnchor constraintEqualToAnchor:reloadButton.trailingAnchor constant:20.0],
[insertButton.widthAnchor constraintEqualToAnchor:reloadButton.widthAnchor],
// constrain tableView Top: 20-pts from buttons / Leading: 0 / Trailing: 0 / Bottom: 0
[tableView.topAnchor constraintEqualToAnchor:reloadButton.bottomAnchor constant:20.0],
[tableView.leadingAnchor constraintEqualToAnchor:g.leadingAnchor constant:0.0],
[tableView.trailingAnchor constraintEqualToAnchor:g.trailingAnchor constant:0.0],
[tableView.bottomAnchor constraintEqualToAnchor:g.bottomAnchor constant:0.0],
]];
[tableView registerClass:[ExampleTableViewCell class] forCellReuseIdentifier:#"exCell"];
tableView.delegate = self;
tableView.dataSource = self;
[reloadButton addTarget:self action:#selector(btnTap:) forControlEvents:UIControlEventTouchUpInside];
[insertButton addTarget:self action:#selector(btnTap:) forControlEvents:UIControlEventTouchUpInside];
}
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
[tipView removeFromSuperview];
}
- (void)btnTap:(UIButton *)btn {
// remove tipView if it's showing
[tipView removeFromSuperview];
NSString *s = sampleStrings[++idx % 3];
if (btn == reloadButton) {
[self reloadMethod:s];
} else {
[self insertMethod:s];
}
}
- (void)insertMethod:(NSString *)s {
// IndexPath for cell you want
__block NSIndexPath *pth = [NSIndexPath indexPathForRow:insertRow inSection:0];
[myData insertObject:s atIndex:pth.row];
[CATransaction begin];
[CATransaction setCompletionBlock:^{
[self showTipView:pth];
}];
[self->tableView insertRowsAtIndexPaths:#[pth] withRowAnimation:UITableViewRowAnimationRight];
[CATransaction commit];
}
- (void)reloadMethod:(NSString *)s {
// IndexPath for cell you want
__block NSIndexPath *pth = [NSIndexPath indexPathForRow:insertRow inSection:0];
[myData insertObject:s atIndex:pth.row];
[tableView reloadData];
dispatch_async(dispatch_get_main_queue(), ^{
[self showTipView:pth];
});
}
- (void)showTipView:(NSIndexPath *)pth {
// get a reference to the cell
ExampleTableViewCell *cell = [tableView cellForRowAtIndexPath:pth];
// if row is not visible
if (!cell) {
return;
}
// get a reference to the cell's stack view
UIStackView *stack = [cell getStackRef];
// add tipView to self.view
[self.view addSubview:tipView];
// constrain tipView
// Leading to stack view's Leading
// Bottom to cell's Top - 4
[NSLayoutConstraint activateConstraints:#[
[tipView.leadingAnchor constraintEqualToAnchor:stack.leadingAnchor constant:0.0],
[tipView.bottomAnchor constraintEqualToAnchor:cell.topAnchor constant:-4.0],
]];
// if we want to "fade-in" the tipView
[tipView setAlpha:0.0];
[UIView animateWithDuration:0.3
animations:^{
[self->tipView setAlpha:1.0];
}];
}
- (nonnull UITableViewCell *)tableView:(nonnull UITableView *)tableView cellForRowAtIndexPath:(nonnull NSIndexPath *)indexPath {
ExampleTableViewCell *c = (ExampleTableViewCell *)[tableView dequeueReusableCellWithIdentifier:#"exCell" forIndexPath:indexPath];
[c configureCell:myData[indexPath.row]];
return c;
}
- (NSInteger)tableView:(nonnull UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
return [myData count];
}
#end