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The approaches here are only valid on 10.4 and previous. See NSSplitView.

This code will collapse a split view if the user double clicks on the split bar. Some issues:

– SaileshAgrawal

This doesn’t “collapse” a subview in the sense of -[NSSplitView isSubviewCollapsed:], it sets the width of the subview to 0. There’s a distinction.*

/*************************************************************************************
 * Function - splitView:canCollapseSubview:
 *
 * Delegate function for SplitView, called when the user clicks on the split
 * bar.  I'm not sure what this function is supposed to do but I use it
 * to capture clicks on the splitBar.
 *
 * If the click was a double click then I collapse/uncollapse the leftView.
 * This requires some hacks.  When the view is uncollapsed and the user double
 * clicks it we get two messages.  When the view is collapsed and the user 
 * double clicks it we get one message.  Thus we keep a counter as follows:
 * x[-1 ==> 0] - the view is open so collapse it
 * x[ 0 ==> 1] - this is a redundant message so ignore it
 * x[ 1 ==> 2] - the view is close so uncollapse it and reset x to -1
 * Another hack is that I always return NO.  If I change this to a YES it
 * stops working.
*************************************************************************************/
- (BOOL)splitView:(NSSplitView *)sender canCollapseSubview:(NSView*)subview  {
    static int x = -1;     
    NSView *leftView = sender subviews] objectAtIndex:0];
    
    if (subview == leftView) {
        [[NSEvent *event = coverMatrix window] currentEvent];
        if ([event type] == [[NSLeftMouseDown && [event clickCount] == 2) {
            // keep count of the number of double click messages we get
            x++;
            
            // this is a redundant message so ignore it
            if (x == 1) return NO;
            
            if (coverMatrixCollapsed) {
                [self uncollapseCoverMatrix:sender];
                x = -1;
            } else {
                [self collapseCoverMatrix:sender];
            }
        }
    }
    return NO;
}

/*************************************************************************************
 * Function - collapseCoverMatrix:
 *
 * Resize the left view so it's width is 0.  We save the old width before
 * collapsing it so if the user double clicks on the splitBar we can
 * restore the view to it's old width.
*************************************************************************************/
- (void) collapseCoverMatrix:(NSSplitView*)splitView {
    float oldPos;
    NSView *leftView=splitView subviews] objectAtIndex:0];
    [[NSView *rightView=splitView subviews] objectAtIndex:1]; 
    [[NSRect leftFrame=[leftView frame];
    NSRect rightFrame = [rightView frame]; 
    
    lastCoverMatrixWidth = leftFrame.size.width;
    lastWhiteViewWidth = rightFrame.size.width;
            
    rightFrame.size.width += leftFrame.size.width;
    [rightView setFrame:rightFrame];
    leftFrame.size.width = 0;
    [leftView setFrame:leftFrame];
    [splitView adjustSubviews];
    coverMatrixCollapsed = TRUE;
}

/*************************************************************************************
 * Function - uncollapseCoverMatrix:
 *
 * Restore the left view to it's previous size.
*************************************************************************************/
- (void) uncollapseCoverMatrix:(NSSplitView*)splitView {
    NSView *leftView=splitView subviews] objectAtIndex:0];
    [[NSView *rightView=splitView subviews] objectAtIndex:1]; 
    [[NSRect leftFrame=[leftView frame];
    NSRect rightFrame = [rightView frame]; 

    leftFrame.size.width = lastCoverMatrixWidth;
    [leftView setFrame:leftFrame];

    rightFrame.size.width = lastWhiteViewWidth;
    [rightView setFrame:rightFrame];
    
    [splitView adjustSubviews];
    coverMatrixCollapsed = FALSE;
}