Objective-c – ios 8 (UITableViewCell) : Constraints ambiguously suggest a height of zero for a tableview cell’s content view

autolayoutios8objective cuitableview

I have a tableview using auto layout constraints , every thing is working in iOS 7 but when i tested in iOS 8 get me the below warning

Warning once only: Detected a case where constraints ambiguously suggest a height of zero for a tableview cell's content view. We're considering the collapse unintentional and using standard height instead.

After i made a profound investigations about this issue i found should add the below lines in viewdidload for iOS8 only

 self.tableView.rowHeight = UITableViewAutomaticDimension;

 self.tableView.estimatedRowHeight = 87;

After that still i get this warning and the height of cell isn't correct which is not take the height from Storyboard

For further info about UITableViewCell find below our constraints for content view cell

-(void) updateConstraints {
    [super updateConstraints];


    if(!didSetupConstraints ) {
       didSetupConstraints = YES;


    [self.contentView removeConstraints:self.contentView.constraints];
    // Interval Title
    //Leading
    constraint = [NSLayoutConstraint constraintWithItem:self.intervalTitle attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.contentView attribute:NSLayoutAttributeCenterX multiplier: 1.0 constant:0.0];
        [self.contentView addConstraint:constraint];

     //Top
    constraint = [NSLayoutConstraint constraintWithItem:self.intervalTitle attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.marketLocationTitle attribute:NSLayoutAttributeTop multiplier:1.0 constant:0.0];
        [self.contentView addConstraint:constraint];
}

Best Answer

Auto Layout is right on that one. It's impossible to calculate cell's height from .CenterX and .Top for the label. One way to resolve the problem would be removing the existing .CenterX constraint and adding a new .Bottom constraint. That way, Auto Layout could easily calculate cell's height.

Related Solutions

Using memcpy to read two integers from a memory block

This is nonstandard:

void *block = ...; 
block + sizeof(int); // where does this point to?

If you want to do pointer arithmetic, cast to a type of known size first (the pointer addition is implicitly multiplied by the size of the underlying type, and sizeof(unsigned char) is always 1):

void *block = ...;
(unsigned char *) block + sizeof(int);

Or use the even easier version,

void *block = ...;
(int *) block + 1;

So the final code is:

int test;
void *block = ...;
memcpy(&test, block, sizeof(test));
// do something...?
memcpy(&test, (int *) block + 1, sizeof(test));

Or a simpler version,

int test[2];
void *block = ...;
memcpy(&test, block, sizeof(test));

Don't do the following:

test = *(int *) block;

It will crash on some systems (typically SIGBUS) if block is unaligned.

R – as3 – Preloading XML Image Gallery

Personally I'm a huge fan of the awesome BulkLoader library:

It's incredibly flexible
It provides useful helpers to access loaded assets (e.g. getBitmap("asset_id") returns a typed object)
It gives meaningful feedback on progress (values can optionally be returned to reflect progress by overall "weight" as opposed to the raw value from individual files that may vary significantly in size)
It handles concurrent loading (which is obviously faster than loading in sequence).

Alternatively, if you want to roll your own solution, as you loop through, add an event listener to the

Event.COMPLETE

notification. In the handler for this event increment a counter; once this counter equals the number of elements you've loaded all your assets.

Pseudo-code:

var loadCounter:int = 0;

var img_arr:Array = [
    "img1_thumb.jpg", "img1.jpg", 
    "img2_thumb.jpg", "img2.jpg", 
    ... 
];
var image_num:int = img_arr.length;

var ldr:Loader;
var req:URLRequest;
var path:String;
var i:int   = 0;
for(; i < image_num; i++) 
{
     path = "http://myserver.com/images/" + img_arr[i];
     req  = new URLRequest(path);
     ldr  = new Loader();
     ldr.contentLoaderInfo.addEventListener(Event.COMPLETE, _onLoadComplete);
     ldr.load(req);
}

private function _onLoadComplete(event:Event):void
{
    if(++loadCounter == image_num)
    {
        // do whatever you need to your loaded assets
    }
}

Best Answer

Related Solutions

Using memcpy to read two integers from a memory block

R – as3 – Preloading XML Image Gallery

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