如何使用显式 NSLayoutManager、NSTextStorage、NSTextContainer 以编程方式设置 NSTextView？

Question

Following the apple documentation I am trying to set up a simple NSTextView via its two constructor methods.

I am placing the below code inside the viewDidAppear method of the view controller of the content view. textView is an instance of NSTextView , frameRect is the frame of the content view.

The following Swift code works (gives me an editable textView with the text showing on the screen):

    textView = NSTextView(frame: frameRect!)
    self.view.addSubview(textView)
    textView.textStorage?.appendAttributedString(NSAttributedString(string: "Hello"))

The following does NOT work (text view is not editable and no text shown on the screen):

    var textStorage = NSTextStorage()
    var layoutManager = NSLayoutManager()
    textStorage.addLayoutManager(layoutManager)
    var textContainer = NSTextContainer(containerSize: frameRect!.size)
    layoutManager.addTextContainer(textContainer)
    textView = NSTextView(frame: frameRect!, textContainer: textContainer)

    textView.editable = true
    textView.selectable = true
    self.view.addSubview(textView)

    textView.textStorage?.appendAttributedString(NSAttributedString(string: "Hello more complex"))

What am I doing wrong in the second example ? I am trying to follow the example given in Apple's "Cocoa Text Architecture Guide" where they discuss setting up an NSTextView by explicitly instantiating its web of helper objects.

Answer 1

You need to keep a reference to the NSTextStorage variable you create. I'm not quite sure about the mechanics of it all, but it looks like the text view only keeps a weak reference to its text storage object. Once this object goes out of scope, it's no longer available to the text view. I guess this is in keeping with the MVC design pattern, where views (the NSTextView in this case) are meant to be independent of their models (the NSTextStorage object).

import Cocoa

@NSApplicationMain
class AppDelegate: NSObject, NSApplicationDelegate {

    @IBOutlet weak var window: NSWindow!

    var textView: NSTextView!
    var textStorage: NSTextStorage! // STORE A REFERENCE

    func applicationDidFinishLaunching(aNotification: NSNotification) {
        var view = window.contentView as NSView
        textStorage = NSTextStorage()
        var layoutManager = NSLayoutManager()
        textStorage.addLayoutManager(layoutManager)
        var textContainer = NSTextContainer(containerSize: view.bounds.size)
        layoutManager.addTextContainer(textContainer)
        textView = NSTextView(frame: view.bounds, textContainer: textContainer)

        textView.editable = true
        textView.selectable = true
        view.addSubview(textView)

        textView.textStorage?.appendAttributedString(NSAttributedString(string: "Hello more complex"))
    }
}

Answer 2

Tested under Xcode 12.4. in Playgrounds:

import Cocoa
import AppKit

let textViewFrame = CGRect(x: 0, y: 0, width: 250, height: 90)
let textStorage = NSTextStorage()
var layoutManager = NSLayoutManager()
textStorage.addLayoutManager(layoutManager)
var textContainer = NSTextContainer(containerSize: textViewFrame.size)
layoutManager.addTextContainer(textContainer)
let textView = NSTextView(frame: textViewFrame, textContainer: textContainer)
textView.isEditable = true
textView.isSelectable = true
textView.textColor = NSColor.red
textView.string = "Why is this so complicated..."

Answer 3

#import <Cocoa/Cocoa.h>

@interface TextViewController : NSObject {

    NSLayoutManager *secondLayout;

    IBOutlet NSSplitView *columnView;
    IBOutlet NSTextView *bottomView;

}

- (IBAction) addColumn: (id)sender;

@end
#import "TextViewController.h"

@implementation TextViewController

- (void)awakeFromNib
{
    NSTextStorage *storage = [bottomView textStorage];
    secondLayout = [NSLayoutManager new];
    [storage addLayoutManager: secondLayout];
    [secondLayout release];
    [self addColumn: nil];
    [self addColumn: nil];
}


- (IBAction) addColumn: (id)sender
{
    NSRect frame = [columnView frame];

    NSTextContainer *container = [[NSTextContainer alloc]
                                  initWithContainerSize: frame.size];
    [container setHeightTracksTextView: YES];
    [container setWidthTracksTextView: YES];

    [secondLayout addTextContainer: container];
    [container release];
    NSTextView *newView = [[NSTextView alloc] initWithFrame: frame
                                              textContainer: container];
    [columnView addSubview: newView];
    [newView release];
}

@end