Allow click and dragging a view to drag the window itself?

Question

I'm using a textured window that has a tab bar along the top of it, just below the title bar.

I've used -setContentBorderThickness:forEdge: on the window to make the gradient look right, and to make sure sheets slide out from the right position.

What's not working however, is dragging the window around. It works if I click and drag the area that's actually the title bar, but since the title bar gradient spills into a (potentially/often empty) tab bar, it's really easy to click too low and it feels really frustrating when you try to drag and realise the window is not moving.

I notice NSToolbar, while occupying roughly the same amount of space below the title bar, allows the window to be dragged around when the cursor is over it. How does one implement this?

Thanks.

Answer 1

I tried the mouseDownCanMoveWindow solution (https://stackoverflow.com/a/4564146/901641) but it didn't work for me. I got rid of that method and instead added this to my window subclass:

- (BOOL)isMovableByWindowBackground {
    return YES;
}

which worked like a charm.

Answer 2

I found this here:

-(void)mouseDown:(NSEvent *)theEvent {    
    NSRect  windowFrame = [[self window] frame];

    initialLocation = [NSEvent mouseLocation];

    initialLocation.x -= windowFrame.origin.x;
    initialLocation.y -= windowFrame.origin.y;
}

- (void)mouseDragged:(NSEvent *)theEvent {
    NSPoint currentLocation;
    NSPoint newOrigin;

    NSRect  screenFrame = [[NSScreen mainScreen] frame];
    NSRect  windowFrame = [self frame];

    currentLocation = [NSEvent mouseLocation];
    newOrigin.x = currentLocation.x - initialLocation.x;
    newOrigin.y = currentLocation.y - initialLocation.y;

    // Don't let window get dragged up under the menu bar
    if( (newOrigin.y+windowFrame.size.height) > (screenFrame.origin.y+screenFrame.size.height) ){
        newOrigin.y=screenFrame.origin.y + (screenFrame.size.height-windowFrame.size.height);
    }

    //go ahead and move the window to the new location
    [[self window] setFrameOrigin:newOrigin];
}

It works fine, though I'm not 100% sure I'm doing it correctly. There's one bug I've found so far, and that's if the drag begins inside a subview (a tab itself) and then enters the superview (the tab bar). The window jumps around. Some -hitTest: magic, or possibly even just invalidating initialLocation on mouseUp should probably fix that.

Answer 3

As of macOS 10.11, the simplest way to do this is to utilize the new -[NSWindow performWindowDragWithEvent:] method:

@interface MyView () {
    BOOL movingWindow;
}
@end

@implementation MyView

...

- (BOOL)mouseDownCanMoveWindow
{
    return NO;
}

- (void)mouseDown:(NSEvent *)event
{
    movingWindow = NO;

    CGPoint point = [self convertPoint:event.locationInWindow
                              fromView:nil];

    // The area in your view where you want the window to move:
    CGRect movableRect = CGRectMake(0, 0, 100, 100);

    if (self.window.movableByWindowBackground &&
        CGRectContainsPoint(movableRect, point)) {

        [self.window performWindowDragWithEvent:event];
        movingWindow = YES;
        return;
    }

    // Handle the -mouseDown: as usual
}

- (void)mouseDragged:(NSEvent *)event
{
    if (movingWindow) return;

    // Handle the -mouseDragged: as usual
}

@end

Here, -performWindowDragWithEvent: will handle the correct behavior of not overlapping the menu bar, and will also snap to edges on macOS 10.12 and later. Be sure to include a BOOL movingWindow instance variable with your view's private interface so you can avoid -mouseDragged: events once you determined you don't want to process them.

Here, we are also checking that -[NSWindow movableByWindowBackground] is set to YES so that this view can be used in non-movable-by-window-background windows, but that is optional.

Answer 4

It works for me after TWO steps:

1. Subclass NSView, override the mouseDownCanMoveWindow to return YES.
2. Subclass NSWindow, override the isMovableByWindowBackground to return YES.

Answer 5

Have you tried overriding the NSView method mouseDownCanMoveWindow to return YES?

Answer 6

It's quite easy:

override mouseDownCanMoveWindow property

override var mouseDownCanMoveWindow:Bool {
    return false
}

Answer 7

If you got a NSTableView in your window, with selection enabled, overriding the mouseDownCanMoveWindow property won't work.

You need instead to create a NSTableView subclass and override the following mouse events (and use the performWindowDragWithEvent: mentioned in Dimitri answer):

@interface WindowDraggableTableView : NSTableView
@end

@implementation WindowDraggableTableView 
{
    BOOL _draggingWindow;
    NSEvent *_mouseDownEvent;
}

- (void)mouseDown:(NSEvent *)event
{
    if (self.window.movableByWindowBackground == NO) {
        [super mouseDown:event]; // Normal behavior.
        return;
    }

    _draggingWindow = NO;
    _mouseDownEvent = event;
}

- (void)mouseDragged:(NSEvent *)event
{
    if (self.window.movableByWindowBackground == NO) {
        [super mouseDragged:event]; // Normal behavior.
        return;
    }

    assert(_mouseDownEvent);
    _draggingWindow = YES;
    [self.window performWindowDragWithEvent:_mouseDownEvent];
}

- (void)mouseUp:(NSEvent *)event
{
    if (self.window.movableByWindowBackground == NO) {
        [super mouseUp:event]; // Normal behavior.
        return;
    }

    if (_draggingWindow == YES) {
        _draggingWindow = NO;
        return; // Event already handled by `performWindowDragWithEvent`.
    }

    // Triggers regular table selection.
    NSPoint locationInWindow = event.locationInWindow;
    NSPoint locationInTable = [self convertPoint:locationInWindow fromView:nil];
    NSInteger row = [self rowAtPoint:locationInTable];
    if (row >= 0 && [self.delegate tableView:self shouldSelectRow:row])
    {
        NSIndexSet *rowIndex = [NSIndexSet indexSetWithIndex:row];
        [self selectRowIndexes:rowIndex byExtendingSelection:NO];
    }
}

@end

Also don't forget to set the corresponding window movableByWindowBackground property as well:

self.window.movableByWindowBackground = YES;

Answer 8

When you set property isMovableByWindowBackground in viewDidLoad, it may not work because the window property of the view is not yet set. In that case, try this:

override func viewDidAppear() {
    self.view.window?.isMovableByWindowBackground = true
}

Answer 9

Thank you! Dimitris' answer solved my issue but I needed it in swift 5. Here is what I came up with.

final class BlahField: NSTextView {
    
    var movingWindow = false
    
    override func mouseDown(with event: NSEvent) {
        movingWindow = false
        let point = self.convert(event.locationInWindow, from: nil)
        if (self.window!.isMovableByWindowBackground && self.frame.contains(point)) {
            self.window?.performDrag(with: event)
            movingWindow = true
            return
        }
    
    }
    
    override func mouseDragged(with event: NSEvent) {
        if (movingWindow) {
            return
        }
    }
}