NSBrowser setRowHeight, not supported for browsers with matrix delegates - objective-c

Question

I have an NSBrowser and try to use setRowHeight, but I get the error:
"setRowHeight: is not supported for browsers with matrix delegates."
I really don't understand what this means, and if someone could help me out by either telling me how to fix it or even just what a matrix delegate is, it would be much appreciated.

Answer 1

A delegate is a helper object that you tell the NSBrowser instance about either by using -setDelegate: in code or hooking the delegate outlet up in IB (the NIB editor). It is commonly used to fill the browser's data, determine programmatically the layout options, etc.
If you have a delegate assigned in your NSBrowser instance, you are expected (required) to give the row height using the delegate method:
- (CGFloat)browser:(NSBrowser *)browser heightOfRow:(NSInteger)row inColumn:(NSInteger)columnIndex
Which will allow you to optionally set the row height on a per-row basis, but in your case, you can safely return a constant.

Answer 2

A NSBrowser creates one instance of NSMatrix per column. The browser itself only manages the columns and leaves row management entirely to the matrices. The matrices display cell objects (NSCell or subclasses of it). A cell is a simple displayable object that knows nothing but how to draw itself. Unlike a view (NSView and subclasses), it never manages an own drawing context, it also doesn't belong to a window (and thus won't ever directly access the window's drawing context) and it knows nothing about the "view hierarchy" (superviews, subviews, view order, constraints, etc.), it just manages some properties, some state and knows how to draw itself to a drawing context provided.
If your delegate works with items (the docs speak about "the item delegate methods"), the developers of NSBrowser thought it's unlikely that you ever want to deal with matrices directly, thus the browser will control all the display aspects for you. You are only supposed to hand out items (basically arbitrary objects) in your delegate and answer questions about them by implementing various delegate methods. E.g.: What is the root item? Is item x a leaf item or has children? How many children does it have? What's child number n of item x? What display object (string, image, etc.) shall I use to display that item?
If you don't work with items, you have to work directly with the cells (NSBrowserCell, a subclass of NSCell) that the matrix owns and is going to display. In that case you are said to be a "browser matrix delegate". That means the browser will only ask you how many rows a column has, setup a matrix with cells for you for that column and finally pass every cell once to your delegate, so you can do something meaningful with it, e.g. fill it with displayable content, otherwise the cell would just be empty, and teach it all the stuff the browser has to know (e.g. setting the leaf property).
As a matrix based delegate has to deal with cells directly, it can as well also deal with the matrices directly and in fact that his exactly what you have to do here. E.g. if you want that all rows of your browser have a height of 50 points, implement the following NSBrowser delegate method:
- (void)browser:(NSBrowser *)browser
didChangeLastColumn:(NSInteger)oldLastColumn
toColumn:(NSInteger)column
{
NSMatrix * matrix = [browser matrixInColumn:column];
CGSize cellSize = [matrix cellSize];
if (cellSize.height != 50) {
cellSize.height = 50;
matrix.cellSize = cellSize;
[matrix sizeToCells];
}
}
Every matrix created by the browser is passed to that method at least once before it gets displayed on screen. In case that matrix is not using a cell height of 50 already, we change that and finally tell the matrix to re-layout; that is important as otherwise it won't recalculate its total height. The if is only to avoid that we call sizeToCells more often than necessary as this call may be rather expensive. In this example all columns get equal row height but of course you can set a different row heights per column.