Question

HEADS UP EDIT: I posted the (simple) answer to this below. No need to waste time looking through all this code. Also see structural suggestions in Jack Lawrence’s answer.

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I’ve set up a UITextField in a tableViewCell that starts out with enabled = NO. Later it is changed to enabled = YES so that it can become first responder and call a keyboard, etc.

But once enabled is NO, it can never be YES again:

tf.enabled = YES;
printf(" Is tf enabled? %d", [tf isEnabled]); // this prints 0 — it refuses to be re-enabled.

Even weirder, if I subclass UITextField and give it a simple custom method, I am able to call that method successfully from the controller — before enabled is set to NO. Once enabled is NO, calling the custom method does nothing. There are no warnings or exceptions; it just doesn’t run.

So the problem isn’t just some trouble with the responder chain. The once-disabled textfield behaves like a black hole.

I did take a look at Apple’s demo for editable textfields in cells, “TaggedLocations,” and they fiddle with enabled with complete impunity: nameField.enabled = NO; and nameField.enabled = YES; and everything goes like clockwork.

There is one other clue: The UIControl class ref says, “If the enabled state is NO, the control ignores touch events and subclasses may draw differently.” But refuse to be re-enabled? Refuse to accept method calls? I don’t get it.

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OK, this is probably more than you really want to look at, but hopefully there are some clues buried in it.

Here are the UITextField subclass’s h and m files:

#import "FooNameFieldForCell.h"

@implementation FooNameFieldForCell

- (BOOL) canBecomeFirstResponder {
    printf("\nCBFR called, self.enabled is %d.", self.enabled); 
    if (self.enabled)
        return YES;
    else
        return NO;
}

- (BOOL) canYouHearMe:(id)sender {
    printf("Yes, I hear you."); 
    return YES;
}

@end

#import <UIKit/UIKit.h>

@interface FooNameFieldForCell : UITextField {

}

- (BOOL) canYouHearMe:(id)sender;

@end

Here’s the cellForRow and the action method:

BOOL bPortrait = UIInterfaceOrientationIsPortrait(self.interfaceOrientation);

// Cell Which Layout
NSString *identifier = nil;
UITableViewCell *cellFooList = nil;
switch (indexPath.row) {
    case 0:
        // this textfield is in row 0
        identifier = bPortrait ? @"cellFooListName_portrait" : @"cellFooListName_landscape";
        cellFooList = [tableView dequeueReusableCellWithIdentifier:identifier];
        if (!cellFooList)
            cellFooList = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:identifier] autorelease];
        break;
    // other rows…
}

// Foo
Foo *Foo = [self.frcFoosAllReg_byName.fetchedObjects objectAtIndex:indexPath.section];

// Cell Fill
switch (indexPath.row) {
    case 0: {
        if (cellFooList.tag == 1) {
            for (UIView *subview in cellFooList.subviews) {
                if (subview.tag == 2) {
                    ((FooNameFieldForCell *)cellFooList).text = Foo.FooName;
                    break;
                }
            }
            break;// dequeued cell, already done 
        }

        // button "Edit"
        // (Yes, I know you’re supposed to put this on the navBar, but as a user I have never liked that metaphor. I’m doing the editability by section/row.) 
        UIButton *btnEditFooName = [UIButton buttonWithType:UIButtonTypeRoundedRect];
        [btnEditFooName addTarget:self action:@selector(presentEditFooName:) forControlEvents:UIControlEventTouchUpInside]; // the selector is where I’m trying to enable the textfield
        // do button setup & framing
        [btnEditFooName setFrame:rectBtnEditFooName];
        [cellFooList.contentView addSubview:btnEditFooName];

        // TEXTFIELD SETUP FOLLOWS   

        // do framing
        FooNameFieldForCell *tfFooName = [[FooNameFieldForCell alloc] initWithFrame:rectFooName]; 
        [tfFooName canYouHearMe:self]; // custom method runs OK here
        tfFooName.text = Foo.FooName;
        tfFooName.enabled = NO;
        tfFooName.tag = 2; // tag to locate among cell's subviews
        [cellFooList.contentView addSubview:tfFooName];
        [tfFooName release];
        // no row selection allowed
        cellFooList.selectionStyle = UITableViewCellSelectionStyleNone;
        // tag as done
        cellFooList.tag = 1;
        break;
    // other cases…
    }
}
return cellFooList;
}

// Called by the Edit button:
- (void) presentEditFooName:(id)sender {

    // Determine which Foo is associated with sender.
    if (![sender isKindOfClass:[UIButton class]])
        return;
    UIView *cell = ((UIButton *)sender).superview.superview;
    if (!cell || ![cell isKindOfClass:[UITableViewCell class]])
        return;
    NSIndexPath *indexPath = [self.tvFooList indexPathForCell:((UITableViewCell *)cell)];
    Foo *Foo = [self.frcFoosAllReg_byName.fetchedObjects objectAtIndex:indexPath.section];

    FooNameFieldForCell *tfFooName = nil;
    for (UIView *subview in cell.subviews) {
        if (subview.tag == 2) {
            tfFooName = subview;
            break;
        }
    }

    // BLACK HOLE
        // because tfFooName is nil. But why? It shows up in the cell.

    tfFooName.enabled = YES; 
    [tfFooName becomeFirstResponder];
    printf("\ntfFooName can become firstResp? %d", tfFooName.canBecomeFirstResponder); // always prints 0, can't be firstResp
    [tfFooName canYouHearMe:self]; // does not run
    printf(" Is tfFooName enabled? %d", [tfFooName isEnabled]); // prints 0, still disabled

}

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Well, my mysterious black hole turns out to be — null! OK, seems obvious now, especially since objective-c allows calls on null. But I’m left with another mystery: The field’s text appears in the cell, so how can it be nil?

Answer 1

As is usual when I’m tearing my hair out, the black hole mystery turned out to be simple.

This…

FooNameFieldForCell *tfFooName = nil;
for (UIView *subview in cell.subviews) {
    if (subview.tag == 2) {
        tfFooName = subview;
        break;
    }
}

…should have been this:

FooNameFieldForCell *tfFooName = nil;
for (UIView *subview in ((UITableViewCell *)cell).contentView.subviews) {
    if (subview.tag == 2) {
        tfFooName = subview;
        break;
    }
}

Custom views are one layer down, in the cell’s contentView, not its direct subviews. Aargh! So much time wasted!