如何制作包含属性文本但仅复制纯文本的 NSTextField

Question

I have an NSTextField subclass which uses a NSTextFieldCell subclass which contains an attributed string. I would like it if when the user copies text that it be copied to the pasteboard without the attributes.

I have tried subclassing NSTextView , overriding copy: and setting isFieldEditor to YES and returning this new editor from the cells fieldEditorForView method. While this copies only the plain text whenever it is used I have text drawn on text drawn on text (and so on ...) and if the underlying attributed string is changed by another control the field editor remains unmodified. When I do not use MyFieldEditor and let the NSTextFieldCell subclass use the default implementation this issue does not occur.

Is there a simpler solution to this problem?

Is there something additional that I need to override or receive delegate messages for?

MyFieldCell.m

- (NSTextView *)fieldEditorForView:(NSView *)controlView
{
    MyFieldEditor *editor = [[MyFieldEditor alloc] init];
    [super setUpFieldEditorAttributes:editor];

    return editor;
}

MyFieldEditor.m

@implementation MyFieldEditor

- (instancetype)init
{
    if ( (self = [super init]) )
    {
        [self setFieldEditor:YES];
    }

    return self;
}

- (NSString *)selectedString
{
    return [[self string] substringWithRange:[self selectedRange]];
}

- (void)copy:(id)sender
{
    [[NSPasteboard generalPasteboard] setString:[self selectedString] forType:NSPasteboardTypeString];
}

@end

Note: I am using ARC.

Display Issue Image

Answer 1

Please find below what should be changed. Tested & works with Xcode 11.2.1 / macOS 10.15.2 with no display issues.

a) No custom NSTextFieldCell and NSTextField are needed, so used just default

b) Change to following in MyFieldEditor.m

- (void)copy:(id)sender
{
    [NSPasteboard.generalPasteboard declareTypes:@[NSPasteboardTypeString] owner:self];
    [NSPasteboard.generalPasteboard setString:[self selectedString] forType:NSPasteboardTypeString];
}

c) Add window delegate method substituting field editor for targeted textfield (this is the valid documented way to provide custom field editors)

- (nullable id)windowWillReturnFieldEditor:(NSWindow *)sender toObject:(nullable id)client {
    if (client == self.textField) { // << in this case it is outlet
        return MyFieldEditor.new;
    }
    return nil;
}

Update:

Overriding NSTextFieldCell as below and assigning it in XIB for targeted NSTextField instead of above NSWindow delegate method gives the same valid behaviour.

@interface MyTextCell: NSTextFieldCell
@end

@implementation MyTextCell
- (nullable NSTextView *)fieldEditorForView:(NSView *)controlView {
    id editor = MyFieldEditor.new;
    [super setUpFieldEditorAttributes:editor];
    return editor;
}
@end

Answer 2

The issue is fieldEditorForView: is called repeatedly. Every time it's called it creates a new MyFieldEditor and doesn't get rid of the old field editor.

An NSWindow has only one field editor which it reuses. I guess the assumption is that any field editor of a given type should only ever be created once and should be reused. As such a static variable referencing the editor and a nil check to create provides a lazy reusable editor.

@interface MyFieldCell: NSTextFieldCell
@end

@implementation MyFieldCell
- (nullable NSTextView *)fieldEditorForView:(NSView *)controlView
{
    static MyFieldEditor *kEditor;

    if ( kEditor ) { return kEditor; }
    kEditor = [[MyFieldEditor alloc] init];

    return kEditor;
}
@end

It would be nice if the editor could be made weak though. Unfortunately NSTextView and its subclasses are incompatible with weak references. If anyone has a cleaver idea around this I am all ears.