how to remove subviews from scrollview?

Question

how do i remove all subviews from my scrollview...

i have a uiview and a button above it in the scrollview something like this....

here is my code to add subview in scroll view

-(void)AddOneButton:(NSInteger)myButtonTag {
lastButtonNumber = lastButtonNumber + 1;

if ((lastButtonNumber == 1) || ((lastButtonNumber%2) == 1)) {
btnLeft = 8;}
else if ((lastButtonNumber == 2) || ((lastButtonNumber%2) == 0)) {
btnLeft = 162;
}
CGRect frame1 = CGRectMake(btnLeft, btnTop, 150, 150);
CGRect frame2 = CGRectMake(btnLeft, btnTop, 150, 150);
UIButton *Button = [UIButton buttonWithType:UIButtonTypeCustom];
Button.frame = frame1;
Button.tag = myButtonTag;
[Button addTarget:self action:@selector(buttonClick:) forControlEvents:UIControlEventTouchUpInside];
[Button setBackgroundColor:[UIColor clearColor]];
[Button setBackgroundImage:[UIImage imageNamed:@"WaitScreen.png"] forState:UIControlStateHighlighted];

    GraphThumbViewControllerobj = [[GraphThumbViewController alloc] initWithPageNumber:[[GraphIdArray objectAtIndex:myButtonTag]intValue]];
    GraphThumbViewControllerobj.view.frame=frame2;
    GraphThumbViewControllerobj.lblCounter.text=[NSString stringWithFormat:@"%d of %d",myButtonTag+1,flashCardsId.count];
    GraphThumbViewControllerobj.lblQuestion.text=[flashCardText objectAtIndex:myButtonTag];
    [myScrollView addSubview:GraphThumbViewControllerobj.view];


[myScrollView addSubview:Button];


if ((lastButtonNumber == 2) || ((lastButtonNumber%2) == 0)) {
btnTop = btnTop + 162;
}
if (btnTop+150 > myScrollView.frame.size.height) {
myScrollView.contentSize = CGSizeMake((myScrollView.frame.size.width), (btnTop+160));}
}

and here is the code to remove subviews

if(myScrollView!=nil)
{
        while ([myScrollView.subviews count] > 0) {
            //NSLog(@"subviews Count=%d",[[myScrollView subviews]count]);
            [[[myScrollView subviews] objectAtIndex:0] removeFromSuperview];
}

alt text http://www.freeimagehosting.net/uploads/e5339a1f51.png

Answer 1

The best and easiest is to use

for(UIView *subview in [scrollView subviews])
{
  [subview removeFromSuperview];
}

This indeed causes crash as the basic rule is array shouldn't modified while being enumerated, to prevent that we can use

[[scrollView subviews] 
           makeObjectsPerformSelector:@selector(removeFromSuperview)];

But sometimes crash is still appearing because makeObjectsPerformSelector: will enumerate and performs selector, Also in iOS 7 ui operations are optimized to perform more faster than in iOS 6, Hence the best way to iterate array reversely and remove

NSArray *vs=[scrollView subviews];
for(int i=vs.count-1;i>=0;i--)
{
    [((UIView*)[vs objectAtIndex:i]) removeFromSuperview];
}

Note : enumerating harms modification but not iterating...

Answer 2

To remove all the subviews from any view, you can iterate over the subviews and send each a removeFromSuperview call:

// With some valid UIView *view:
for(UIView *subview in [view subviews]) {
    [subview removeFromSuperview];
}

This is entirely unconditional, though, and will get rid of all subviews in the given view. If you want something more fine-grained, you could take any of several different approaches:

• Maintain your own arrays of views of different types so you can send them removeFromSuperview messages later in the same manner
• Retain all your views where you create them and hold on to pointers to those views, so you can send them removeFromSuperview individually as necessary
• Add an if statement to the above loop, checking for class equality. For example, to only remove all the UIButtons (or custom subclasses of UIButton) that exist in a view, you could use something like:

// Again, valid UIView *view:
for(UIView *subview in [view subviews]) {
    if([subview isKindOfClass:[UIButton class]]) {
        [subview removeFromSuperview];
    } else {
        // Do nothing - not a UIButton or subclass instance
    }
}