Get UIBarButtonSystemItem back from UIBarButtonItem

Question

trying to unit test that I set the correct UIBarButtonSystemItem on my navbar buttons.

I can get the style back but can't seem to find a way to get the UIBarButtonSystemItem

enums that were set for the buttons.This fails because the style is a different enum than

the UIBarButtonSystemItem:

- (void)test_init_should_set_left_right_barButtonItems {

    UIBarButtonItem *left = mainVCSUT.navigationItem.leftBarButtonItem;
    UIBarButtonItem *right = mainVCSUT.navigationItem.rightBarButtonItem;
    [Assert isNotNil:left];
    [Assert isNotNil:right];

    UIBarButtonItemStyle leftStyle = left.style;
    UIBarButtonItemStyle rightStyle = right.style;

    [Assert that:[The int:leftStyle] is:[Equal to:[The int:UIBarButtonSystemItemRefresh]]];
    [Assert that:[The int:rightStyle] is:[Equal to:[The int:UIBarButtonSystemItemSearch]]];
}

Answer 1

On iOS 6.1 at least (I haven't tested other version) UIBarButtonItem has an undeclared method systemItem, which returns the value passed in to the initializer. You can easily access it with key-value coding:

UIBarButtonSystemItem systemItemIn = UIBarButtonSystemItemAdd;
UIBarButtonItem *item = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:systemItemIn target:nil action:NULL];
NSNumber *value = [item valueForKey:@"systemItem"];
UIBarButtonSystemItem systemItemOut = [value integerValue];
NSLog(@"systemItemIn = %d, systemItemOut = %d", systemItemIn, systemItemOut);

If that doesn't work, you can create a typedef for an internal anonymous struct that's an instance variable of the UIBarButtonItem class that stores this information, and use the private ivar's name, and the Objective C run time, as shown below:

//Copied from UIBarButtonItem.h, this is the struct used for the _barButtomItemFlags ivar
typedef struct {
    unsigned int enabled:1;
    unsigned int style:3;
    unsigned int isSystemItem:1;
    unsigned int systemItem:7;
    unsigned int viewIsCustom:1;
    unsigned int isMinibarView:1;
    unsigned int disableAutosizing:1;
    unsigned int selected:1;
    unsigned int imageHasEffects:1;
} FlagsStruct;

// In our test code
// Instantiate a bar button item
UIBarButtonSystemItem systemItemIn = UIBarButtonSystemItemAdd;
UIBarButtonItem *item = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:systemItemIn target:nil action:NULL];

// Set up variables needed for run time functions
Class barItemClass = [item class];
BOOL foundIt = NO; // We check this flag to make sure we found the ivar we were looking for
ptrdiff_t ivarOffset = 0; // This will be the offset of _barButtomItemFlags within the bar button item object

// Iterate through all of UIBarButtonItem's instance variables
unsigned int ivarCount = 0;
Ivar *ivarList = class_copyIvarList(barItemClass, &ivarCount);
for (int i = 0; i < ivarCount; i++) {
    Ivar ivar = ivarList[i];
    const char *ivarName = ivar_getName(ivar);
    if (!strcmp(ivarName, "_barButtonItemFlags")) {
        // We've found an ivar matching the name. We'll get the offset and break from the loop
        foundIt = YES;
        ivarOffset = ivar_getOffset(ivar);
        break;
    }
}
free(ivarList);

if (foundIt) {
    // Do a little pointer math to get the FlagsStruct - this struct contains the system item value.
    void *itemPointer = (__bridge void *)item;
    FlagsStruct *flags = itemPointer + ivarOffset;
    UIBarButtonSystemItem systemItemOut = flags->systemItem;
    NSLog(@"systemItemIn = %d, systemItemOut = %d", systemItemIn, systemItemOut);
    BOOL equal = (systemItemIn == systemItemOut);
    if (equal) {
        NSLog(@"yes they are equal");
    }
    else {
        NSLog(@"no they are not");
    }
}
else {
    // Perhaps Apple changed the ivar name?
    NSLog(@"didn't find any such ivar :(");
}

Either way you approach it, it's possible it will change, so I'd maybe suggest having your tests run conditionally only on versions of the OS verified to support either of these approaches.