MacOS 开发（五）：NSTextView纯代码实现

因为系统机制导致，纯代码实现滚动视图的时候必须自己实现 scrollView，随封装如下：

🌰🌰：
- (void)viewDidLoad {
    [super viewDidLoad];

    [self.view addSubview:self.textView.enclosingScrollView];
}

- (void)viewDidLayout{
    [super viewDidLayout];

    [self.textView.enclosingScrollView makeConstraints:^(MASConstraintMaker *make) {
        make.top.equalTo(self.view);
        make.left.equalTo(self.view);
        make.width.equalTo(self.view).multipliedBy(0.5);
        make.bottom.equalTo(self.view).offset(0);
    }];
  //备注：textView.enclosingScrollView 和 textView.scrollView 是同一对象
}

#pragma mark -lazy
-(UUTextView *)textView{
    if (!_textView) {
        _textView = ({
            UUTextView * view = [UUTextView create:CGRectZero];
            view.delegate = self;
            view.string = @"NSScrollView上无法滚动的NSTextView";
            view.font = [NSFont systemFontOfSize:12];
            
            view;
        });
    }
    return _textView;
}

视图封装：

class UUTextView: NSTextView {

    lazy var scrollView: NSScrollView = {
        let scrollView = NSScrollView()
        scrollView.backgroundColor = NSColor.red
        scrollView.drawsBackground = false
        scrollView.hasHorizontalScroller = true
        scrollView.hasVerticalScroller = true
        scrollView.autohidesScrollers = true
        
        return scrollView
    }()
    
    var placeHolder: String?
    
    // MARK: -lifecycle
    override init(frame frameRect: NSRect, textContainer container: NSTextContainer?) {
        super.init(frame: frameRect, textContainer: container)
        
        setupUI()
    }
    
    override init(frame frameRect: NSRect) {
        super.init(frame: frameRect)
        
        setupUI()
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func draw(_ dirtyRect: NSRect) {
        super.draw(dirtyRect)

        // Drawing code here.
        if string == "" && self != window?.firstResponder {
            guard let placeHolder = placeHolder else { return }
            let attDic = [NSAttributedString.Key.foregroundColor: NSColor.gray]
            let attString = NSAttributedString(string: placeHolder, attributes: attDic)
            attString.draw(at: NSMakePoint(4, 0))
        }
    }
    
    override func resignFirstResponder() -> Bool {
        needsDisplay = true
        return super.resignFirstResponder()
    }
    
    // MARK: -funtions
    func setupUI() {
        scrollView.documentView = self
    }
    
}