Quickies for NSView

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Quickies for NSView

Debugging

Outlining every view [permalink]
You can set the NSShowAllViews default value to have every view outlined. Nested views get outlined in different colors.
Set it "permanently" via
```
% defaults write com.apple.TextEdit NSShowAllViews YES
```
(or whatever your application identifier is), or use the one-shot version:
```
/Developer/Applications/Xcode.app/Contents/MacOS/Xcode -NSShowAllViews YES
```

General

Checking for modifier keys [permalink]
In your mouseDown:
```
    if ([event modifierFlags] & NSShiftKeyMask) {
        constrain = YES;
    } 
```
If you need to check them outside of your mouseDown, and if you're on 10.6 or beyond, you can use +[NSEvent modifierFlags];
If you're stuck in 10.5 or older, you need to do something like this: dip into carbon:
- GetCurrentEventKeyModifiers returns the modifiers of the last event processed by the event dispatcher. This is usually sufficient.
- GetCurrentKeyModifiers returns the hardware state of the modifiers.
Carbon and AppKit use different constants for the modifiers, however, so you may need to convert between them depending on your situation. (Thanks to Peter Hosey for the Carbon trick)
(Thanks to Mike Ash for pointing out the new 10.6 API)
Converting an event to view coordinates [permalink]
NSPoint point = [self convertPoint: [event locationInWindow] fromView: nil];

Detecting arrow keys [permalink]

- (void) keyDown: (NSEvent *) event
{
    NSString *characters;
    characters = [event characters];

    unichar character;
    character = [characters characterAtIndex: 0];

    if (character == NSRightArrowFunctionKey) {
        [self moveSelectedBlockBy: 1];

    } else if (character == NSLeftArrowFunctionKey) {
        [self moveSelectedBlockBy: -1];

    }  ... and look at whatever other keys you want
}

Finding a subview based on tag [permalink]
Sometimes you're in a situation where you need to get ahold of a view and it's not convenient to set up stuff in IB (like the object needing to get the view isn't in the nib file with the window). You can uses NSView's viewWithTag: to find it.
Grabbing a view into an image [permalink]
In your NSView subclass:
```
[self lockFocus];

NSBitmapImageRep *bits;
bits = [[NSBitmapImageRep alloc]
           initWithFocusedViewRect: [self bounds]];
[self unlockFocus];
```
Then you can add it to an NSImage or save it to a file, or whatever.
If you want to retain the vectoritude of the drawing, you can use [self dataWithPDFInsideRect: [self bounds]], and then make an NSPDFImageRep. Avoid the NSEPSImageRep since it makes a trip through NSPDFImageRep along with a slow PS to PDF conversion. (Thanks to Peter Hosey for the PDF hint)

Making a custom event tracking runloop [permalink]
Sometimes in your mouse tracking code you want to use the NSEventTrackingRunLoopMode, such as you wanting to use an NSNotificationQueue to coalesce updates for your own mouse tracking code. I've been sticking a call to this in my mouseDown: handler for the cases when I want the secondary run loop

- (void) runEventTrackingRunLoop
{
    NSEventType eventType = NSLeftMouseDown;

    unsigned int eventMask = NSLeftMouseDownMask | NSLeftMouseUpMask
        | NSLeftMouseDraggedMask | NSMouseMovedMask;

    while (eventType != NSLeftMouseUp) {
        NSEvent *event;
        event = [NSApp nextEventMatchingMask: eventMask
                       untilDate: [NSDate distantFuture]
                       inMode: NSEventTrackingRunLoopMode
                       dequeue: YES];

        eventType = [event type];

        if (eventType == NSLeftMouseDragged) {
            [self mouseDragged: event];
        }
    }

} // runEventTrackingRunLoop

(and thanks to Rainer Brockerhof for pointing out a no-op line of code from the original version of this)

Performing relative (grab-hand) scrolling [permalink]
Grab-hand scrolling is a handy feature in several apps. It's nice being able to scroll around a large document diagonally, fer instance. Here's one way to do it (assuming you have a standard NSScrollView -> NSClipView -> YourView setup)

@interface Blah : NSView
{
    NSPoint grabOrigin;
    NSPoint scrollOrigin;
}
@end // Blah

...

@implementation Blah

...

- (void) mouseDown: (NSEvent *) event
{
    // deal in window coordinates.  there is a scrolling problem
    // if using view coordinates because view coordinates
    // can get transformed
    grabOrigin = [event locationInWindow];

    NSClipView *contentView;
    contentView = (NSClipView*)[layerView superview];

    scrollOrigin = [contentView bounds].origin;

} // mouseDown


- (void) mouseDragged: (NSEvent *) event
{
    NSPoint mousePoint;
    mousePoint = [event locationInWindow];

    float deltaX, deltaY;
    deltaX = grabOrigin.x - mousePoint.x;
    deltaY = mousePoint.y - grabOrigin.y;

    NSPoint newOrigin;
    newOrigin = NSMakePoint (scrollOrigin.x + deltaX,
                             scrollOrigin.y + deltaY);

    [layerView scrollPoint: newOrigin];

} // mouseDragged
...

@end // Blah

You can be fancy and check for the option key by look at [event modifierFlags] and looking for NSAlternateKeyMask, and also use the NSCursor open/closedHandCursor.

Reacting to the Escape key [permalink]
There's no predefined constant for the Escape key. Luckily the escape key predates every personal computer, and so it has a pretty reliable character value that's generated: 27:
```
- (void) keyDown: (NSEvent *) event
{
    NSString *chars = [event characters];
    unichar character = [chars characterAtIndex: 0];

    if (character == 27) {
        NSLog (@"ESCAPE!");
    }
} // keyDown
```

Reacting to the delete key [permalink]
Look for NSDeleteCharacter in the event's character string:

- (void) keyDown: (NSEvent *) event
{
    NSString *chars = [event characters];
    unichar character = [chars characterAtIndex: 0];

    if (character == NSDeleteCharacter) {
        NSLog (@"Delete!");
    }
} // keyDown

Responding to modifier keys only [permalink]
NSView's keyDown: and keyUp: don't fire when just a modifier key goes down. If you do want to react to this, you'll need to override flagsChanged: (NSEvent *) event and look at the event there. (flagsChanged: comes from NSResponder, so any responder in the responder chain can react to it)
Setting a cursor for a view [permalink]
Sometimes you want to change the cursor for a view, say with a crosshair for a view that lets you select a rectangle out of an image. There is no -[NSView setCursor:] call (drat!) You can get something similar by adding this to your NSView subclass:
```
- (void) resetCursorRects
{
    [super resetCursorRects];
    [self addCursorRect: [self bounds]
          cursor: [NSCursor crosshairCursor]];

} // resetCursorRects
```

Hacks

Becoming firstResponder if you don't have an editable cell [permalink]
You make a custom view, add it to your window in Interface Builder, and you make it the first responder. When you run the program, your custom view is not the first responder, instead some lame-O textfield has snagged keyboard focus. To address this, override this undocumented method:
```
- (BOOL) _hasEditableCell
{
    return (YES);
} // _hasEditableCell
```
This workaround is necessary at least for Mac OS X 10.1.*.

Swift

Implementing -isFlipped in Swift [permalink]
Trying to do an override or other methody way of isFlipped results in the usual inscrutible Swift error messages. Do it this way instead:
```
    override var flipped: Bool {
        return true
    }
```