I know there is a property or method that makes the scrollview/uiview call drawRect: method while is scrolling. By default is disabled because of performance reasons but I need to enable it.
I cannot remember the name of the method hence I cannot look for it, anyone who knows what I am looking for?
Thanks in advance
I'ld suggest to use the scrollViewDidScroll:-method and then redraw the view.
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
[someView setNeedsDisplay];
}
Related
Is there an easy way for listening for when a child or subview has been added to a UIView?
I've gone through the addobserver options and haven't found an obvious option anyway. There may be another option that would be affected though when content is added to a view or am I wrong in saying that? i.e. content width or height, positions, etc.?
Edit
This is accomplished easily using the advice of #Alkimake below (TextHolderClass).
I created a custom UIView subclass and set the UIView's class in Interface Builder to be equal to TextHolderClass
Thanks for your help, I know it should have been obvious :)
UIView methods may help you:
- (void)willMoveToSuperview:(UIView *)newSuperview
UIView has 2 methods to call after subview interactions. Simply create your custom UIView class and implement these methods which is pretty for you. And use your own CustomView
- (void)didAddSubview:(UIView *)subview;
- (void)willRemoveSubview:(UIView *)subview;
I've got my own dynamically changing view inside scrollview.
As my view is very big I usually redraw only it's visible part.
But when I scroll up or down drawRect method isn't being called.
I guess scroll view has a buffer to quickly react on user actions but I don't know exactly a mechanism how it works.
UPD
Thanks to Wienke, I've got a solution: to implement UIScrollViewDelegate.
I've implemented scrollViewDidScroll method:
-(void) scrollViewDidScroll:(UIScrollView *)sender {
CGRect visibleRect;
visibleRect.origin = [scrollView contentOffset];
visibleRect.size = [scrollView bounds].size;
[textField setNeedsDisplayInRect:visibleRect];
}
So every time user scrolls even a little this method redraws the whole visible part. That's bad=(
How can I redraw only... Let me call that "new region that appeared after scrolling". I guess it's much faster...
Thanks for your attention.
Have you tried assigning a scrollview delegate? The UIScrollViewDelegate protocol includes methods like scrollViewDidEndDragging, upon which you could redraw.
I am subclassing a UIView and overwrite the drawRect method. I'm noticing that the view's drawrect is only being called when the view first loads. After that it is never called again. How to I make sure it gets called after an orientation change? I've tried calling setNeedsDisplay on the view before and after the rotation and that doesn't do it.
[myView setContentMode:UIViewContentModeRedraw];
You can set this in IB as well (i.e., set mode to "redraw")
This was a bug related to something completely different. setNeedsDisplay does indeed cause drawRect to be called.
to answer this and the other 94,000 similiar questions about view rotation/drawrect funkiness,
-(id)initWithFrame:(CGRect)frame
{
if(self=[super initWithFrame:frame]) {
self.autoresizesSubviews=YES;
self.autoresizingMask=UIViewAutoresizingFlexibleWidth|UIViewAutoresizingFlexibleHeight;
}
return self;
}
In the iPhone 3.0 SDK, how can I be informed when a zoomToRect:animated: animation completes?
Sometimes the scrollview doesn't zoom at all (if it's already at the proper zoom level), and there doesn't seem to be a way to detect that.
On your delegate, you can listen for - (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(float)scale
see UIScrollView and UIScrollViewDelegate
The easiest way would probably to put in a check before starting the animation. If the zoom level is already correct, call [self performSelectorOnMainThread:#selector(myMethod) withObject:id waitUntilDone:NO].
You won't be able to use the same method as scrollViewDidEndZooming, because you can only pass one argument, but it will trigger an asynchronous call on the main thread
I have added several UIScrollViews as subviews of a single UIView and set the frames so that each one is clearly visable. I set scrollEnabled to YES and set the contentSize larger than the bounds/frame. I do this in a for loop, and with each pass of the loop I release the UIScrollView (though the object is still stored because it has been subviewed into the UIView). This works well for being able to scroll around the imageView stored in each particular UIScrollView but I cannot for the life of me figure out how to get the zoom to work. I included the in the interface. Here are the methods I have tried for choosing the correct view for zooming:
- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView{
return [[myView subviews] objectAtIndex:pageNum];
}
and
- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView{
return [myView viewWithTag:pageNum];
}
neither seems to work. The weird part is that scrolling works fine. I can't even get the viewForZooming method to get called at all if I put in an NSLog call. Any ideas? I think I've lost all my hair from getting frustrated with this.
Edit: Thanks a lot cduhn! All I needed was that little bump, I had forgotten to set the scrollView delegate to self... I've been working with various apps that take advantage of UIScrollView for months now and been using the delegate correctly and this most recent one I don't know where my brain went.
However, you do not need to override the scrollViewDidEndZooming:withView:atScale:, the delegate will call that no matter what after a zoom.
Also, after a little tweeking this worked:
- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView{
return [[[myView viewWithTag:pageNum] subviews] objectAtIndex:0];
}
This simply calls the scrollView inside View container and then gets the UIImage inside of that... works well.
It sounds like you may not have set the delegate property on your UIScrollViews to point at the object that implements viewForZoomingInScrollView:
Also note this snippet from the UIScrollView Class Reference:
For zooming and panning to work, the delegate must implement both viewForZoomingInScrollView: and scrollViewDidEndZooming:withView:atScale:; in addition, the maximum (maximumZoomScale) and minimum ( minimumZoomScale) zoom scale must be different.
Finally, a word of warning: Be careful when accessing the subviews of UIScrollView. Your subviews are not alone in there. UIScrollView adds its own UIImageViews as subviews of itself to implement its scrollbar UI. So code like this...
- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView {
return [[myView subviews] objectAtIndex:pageNum];
}
... may not do what you expect.