Incorporating old-style view (Audio Unit View) into auto layout

Question

I would like to embed a custom view created by an Audio Unit into a window that uses Auto Layout. After trying dozens of combinations, I still haven't found a way to do this which works with a large selection of Audio Units.

The goal would be to create a container NSView object with the Audio Unit View as a subview, and to set constraints in such a way that the size of the container matches that of the AU view, including when the latter resizes itself. The container should have translatesAutoresizingMaskIntoConstraints set to NO, so it plays nice with the rest of the window.

My first attempt was to create two constraints simply forcing the size of both (container and AU) views to be equal. This fails as the AU view then collapses to a very small size.

Another attempt was to create fixed size constraints for the container view that are initialised to match the AU view, to listen for NSViewFrameDidChangeNotification for the AU view, and to adjust the fixed sizes as required. This crashes as soon as the AU view wants to resize itself. The reason is that when I increase the size of the container to match the AU view, the autoresizing mask constraints instruct the AU view to increase its size again, causing an infinite loop.

What works best so far is to turn translatesAutoresizingMaskIntoConstraints off for the AU view and to set the size of the container by listening to frame change notifications. This appears to work for all AUv2 Audio Units, but for AUv3 Audio Units (in particular Apple's demo AUv3), I always get a view size of (1,1) which is obviously useless. I would be very grateful for any insight into how to make this work...

Answer 1

Based on the sample project you provided this should work:

@interface MyViewController ()
{
    NSLayoutConstraint *widthConstraint, *heightConstraint;
}
@end

@implementation MyViewController


-(void)setFormatForBus:(AUAudioUnitBus*)bus
{
    AudioStreamBasicDescription fmt = {44100, kAudioFormatLinearPCM, kAudioFormatFlagIsNonInterleaved | kAudioFormatFlagIsFloat | kAudioFormatFlagIsPacked, 4, 1, 4, 2, 32, 0};  // Stereo audio on each bus
    AVAudioFormat* format = [[AVAudioFormat alloc] initWithStreamDescription:&fmt];
    NSError* error = nil;
    if (![bus setFormat:format error:&error]) {
        NSLog(@"Couldn't set the format for bus... %@", error);
        return;
    }
    
    bus.enabled = YES;
}

-(void)doLoad:(AVAudioUnit*)node controller:(NSViewController*)viewController
{
    NSView* auView = nil;
    if (viewController == nil) {
        auView = [[AUGenericView alloc] initWithAudioUnit:node.audioUnit displayFlags:(AUViewPropertiesDisplayFlag | AUViewParametersDisplayFlag)];
        auView.frame = self.view.frame;
        [self.view addSubview:auView];
    }
    else {
        self.auViewController = viewController;
        auView = self.auViewController.view;
        auView.translatesAutoresizingMaskIntoConstraints = NO;
        [self.view addSubview:auView];
    }

    NSSize size = _auViewController.view.frame.size;

    widthConstraint = [NSLayoutConstraint constraintWithItem:self.view attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:size.width];
    heightConstraint = [NSLayoutConstraint constraintWithItem:self.view attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:size.height];

    [self.view addConstraints:@[widthConstraint, heightConstraint]];

    NSLayoutConstraint* top = [NSLayoutConstraint constraintWithItem:self.view attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:auView
                                                           attribute:NSLayoutAttributeTop multiplier:1.0 constant:0];
    NSLayoutConstraint* bottom = [NSLayoutConstraint constraintWithItem:self.view attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:auView
                                                              attribute:NSLayoutAttributeBottom multiplier:1.0 constant:0];
    NSLayoutConstraint* left = [NSLayoutConstraint constraintWithItem:self.view attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:auView
                                                            attribute:NSLayoutAttributeLeft multiplier:1.0 constant:0];
    NSLayoutConstraint* right = [NSLayoutConstraint constraintWithItem:self.view attribute:NSLayoutAttributeRight relatedBy:NSLayoutRelationEqual toItem:auView
                                                             attribute:NSLayoutAttributeRight multiplier:1.0 constant:0];

    [self.view addConstraints:@[top, bottom, left, right]];
}

- (void)viewDidLoad {
    [super viewDidLoad];

    NSArray* list = [[AVAudioUnitComponentManager sharedAudioUnitComponentManager] componentsPassingTest: ^BOOL(AVAudioUnitComponent *comp, BOOL *stop) {
        return [comp.typeName containsString:@"Effect"];
    }];
    
    AVAudioUnitComponent* component = nil;
    for (AVAudioUnitComponent* comp in list) {
        if ([comp.name containsString:@"MultibandCompressor"])  // That allows itself to be squashed. Also, it doesn't resize itself when "details" is toggled
//        if ([comp.name containsString:@"FilterDemo"]) // That one is squashed both vertically and horizontally... (Apple's sample AUv3 Audio Unit, needs to be installed first.)
//        if ([comp.name containsString:@"GraphicEQ"])  // That one is squashed vertically
//                    if ([comp.name containsString:@"AUDelay"])
            component = comp;
    }
    
    [AVAudioUnit instantiateWithComponentDescription:component.audioComponentDescription options:0
                                   completionHandler:^(__kindof AVAudioUnit *audioUnit, NSError *error) {
        if (error) {
            NSLog(@"Error instantiating AU: %@", error);
            return;
        }
        
        self.audioUnit = audioUnit;
        AUAudioUnitBusArray* inputBusses = audioUnit.AUAudioUnit.inputBusses;
        AUAudioUnitBusArray* outputBusses = audioUnit.AUAudioUnit.outputBusses;
        
        if (!inputBusses.count || !outputBusses.count) {
            NSLog(@"No busses...");
            return;
        }
        
        [self setFormatForBus:[inputBusses objectAtIndexedSubscript:0]];
        [self setFormatForBus:[outputBusses objectAtIndexedSubscript:0]];
        
        NSError* AUerror = nil;
        if (![audioUnit.AUAudioUnit allocateRenderResourcesAndReturnError:&AUerror]){
            NSLog(@"Error allocating resources: %@", AUerror);
            return;
        }
        [audioUnit.AUAudioUnit requestViewControllerWithCompletionHandler:^(NSViewController* viewController) {
            dispatch_async(dispatch_get_main_queue(), ^{
                [self doLoad:audioUnit controller:viewController];
            });
        }];
    }];
}

- (void)viewWillLayout
{
    [super viewWillLayout];
    if(_auViewController != nil) {
        [self.view removeConstraints:@[widthConstraint, heightConstraint]];
        NSSize size = _auViewController.view.frame.size;
        widthConstraint.constant = size.width;
        heightConstraint.constant = size.height;
        [self.view addConstraints:@[widthConstraint, heightConstraint]];
    }
}

@end