A few questions regarding UILabel and UIImageView placement handling? - iphone

Question

I have two questions regarding the placement and handling UILabel's and UIImageView's:
a. I'd like to know if its possible to detect the location of the "edge" of the text in a UILabel, to put a UIImageView a certain distance to the left or right of the UILabel (with the same height), for example: (UILabel -certain distance in width- UIImageView). (Preferably a method that could be used to detect the edges of a UIImageView as well)
b. I'd also like to know how the creation of UILabel's and UIImageView's programmatically works, I understand that to create for example a UIImageView it's as simple as:
UIImageView *myImgView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 0, 0)];
but I'd like to know: If I have a method to create a UIImageView programmatically, and it sets the CGRect based on a factor that changes, would I need a new name for every UIImageView I create in code, or could I use the same name and add them every time the method runs by calling addSubView? If I do need to individually name them all, and I'm unsure how many I will need to create (because it depends on the user), what is the best method to go about this? If I can create them all with the same name, will they all respond to the same name? Example, if I set myImgView to hidden, will this effect all the UIImageView's named myImgView?

Answer 1

You seem to be new to object oriented programming (as evidenced by the last part), and I would highly recommend you read this: Object-Oriented Programming with Objective-C
But I will answer your question about the UIViews. UIImageView and UILabel are both subclasses of the UIView class. UIView has a special kind of variable called a property. That means that the variable can be set on an instance of that class by another class and can then be accessed from other classes as well. UIView has the frame property that contains the outline of the view in a CGRect. When you have a bit of code like
ImageView *myImgView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 0, 0)];
You are creating an instance of the UIImageView class, allocating memory for it, and initializing it with a frame (in this case you are using rect with zero height and width, which is a bit useless). In order to set the frame to something useful, you use the format CGRectMake(originX, originY, width, height). Keep in mind that on iOS, the origin is on the upper left hand corner of the view, and a higher y value will be farther down the screen. If you need to change the frame later, rather than creating a whole new instance, you can simply alter the property on the existing instance:
myImgView.frame = CGRectMake(10, 20, 50, 100);
//this will make the frame of myImgView to a rectangel 10 units off of the right side of the view, 20 units down from the top of the view, and have a width of 50 units and a height of 100 units
However, you have declared myImgView as a local variable, meaning that you can only access it in the function that you have declared it in, at the time that you have declared it. In order to access it anywhere and anytime, you will need to declare it as an Instance Variable, meaning that you declare it in the .h file.
#interface MyView : UIView {
UIImageView *myImgView;
}
#end
Then the variable will be accessible anywhere in that class. Altering its frame as I demonstrated above will alter the frame in the view.
Finally, you can get the frame of an view if you need to do calculations with it. For example, you can get the frame of myImgView like so:
CGRect viewFrame = myImgView.frame;
CGPoint origin = myImgView.frame.origin;
CGSize width = myImgView.frame.size;
float x = myImgView.frame.origin.x;
float height = myImgView.frame.size.height;
//I think you can get it from here
Now with UILabels, it can be a bit trickier. The frame for a UILabel does not necessarily match the frame that the text takes up. Usually the actual frame is a bit smaller. In order to get the frame for the text of a UILabel, use something like this:
//UILabel *myLabel has been declared either in the .h or earlier in the function
CGRect textFrame = CGRectMake(myLabel.x, myLabel.y, [myLabel.text sizeWithFont:myLabel.font].width, [myLabel.text sizeWithFont:myLabel.font].height);
Now, finally, to put it all together, this would be how to calculate a new frame for your UIImageView:
myImgView.frame = CGRectMake(myLabel.x + [myLabel.text sizeWithFont:myLabel.font].width, yOrigin, width , height);
//where myImgView is your UIImageView myLabel is your UILabel, yOrigin is the y value of the origin of the imageView, and width and height are the width and height of the image.
Well I hope that helps and I highly suggest you read the object oriented programming guide.