crashes my app [NSMutableArray1 removeAllObjects] iphone sdk - iphone

Question

i use this code to check if any objects exist in my NSMutableArray
if yes i remove them all but it crashes although there are objects why?
if([NSMutableArray1 count]==1)
{
[poemoptionslist removeAllObjects];
}
if ([NSMutableArray1 count]==0)
{
[poemoptionslist addObject: final1];
}
CONSOLE OUTPUT
2010-10-18 03:42:13.166
app1[33398:207] * Terminating app
due to uncaught exception
'NSInternalInconsistencyException',
reason: '-[__NSCFArray
removeObjectAtIndex:]: mutating method
sent to immutable object'
* Call stack at first throw: ( 0 CoreFoundation
0x02e55b99 exceptionPreprocess + 185
1 libobjc.A.dylib
0x02fa540e objc_exception_throw + 47
2 CoreFoundation
0x02e0e238 +[NSException
raise:format:arguments:] + 136 3
CoreFoundation
0x02e0e1aa +[NSException
raise:format:] + 58 4
CoreFoundation
0x02e4d3c1 -[__NSCFArray
removeObjectAtIndex:] + 193 5
CoreFoundation
0x02dfe973 -[NSMutableArray
removeAllObjects] + 83 6
poemsoflove
0x0004dc8d -[submitpoem submitpoem:] +
18560 7 UIKit
0x003b77f8 -[UIApplication
sendAction:to:from:forEvent:] + 119 8
UIKit
0x00442de0 -[UIControl
sendAction:to:forEvent:] + 67 9
UIKit
0x00445262 -[UIControl(Internal)
_sendActionsForEvents:withEvent:] + 527 10 UIKit
0x00443e0f -[UIControl
touchesEnded:withEvent:] + 458 11
UIKit
0x003db3d0 -[UIWindow
_sendTouchesForEvent:] + 567 12 UIKit
0x003bccb4 -[UIApplication sendEvent:]
+ 447 13 UIKit 0x003c19bf _UIApplicationHandleEvent +
7672 14 GraphicsServices
0x033e6822 PurpleEventCallback + 1550
15 CoreFoundation
0x02e36ff4
__CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION
+ 52 16 CoreFoundation 0x02d97807 __CFRunLoopDoSource1 + 215
17 CoreFoundation
0x02d94a93 __CFRunLoopRun + 979 18
CoreFoundation
0x02d94350 CFRunLoopRunSpecific + 208
19 CoreFoundation
0x02d94271 CFRunLoopRunInMode + 97 20
GraphicsServices
0x033e500c GSEventRunModal + 217 21
GraphicsServices
0x033e50d1 GSEventRun + 115 22 UIKit
0x003c5af2 UIApplicationMain + 1160
23 poemsoflove
0x00002728 main + 102 24 poemsoflove
0x000026b9 start + 53 25 ???
0x00000001 0x0 + 1 ) terminate called
after throwing an instance of
'NSException' Program received signal:
“SIGABRT”.
Guys there is no NSArray!
I save to NSUSerdefaults like this:
if ([mutable1 count]==0)
{
[mutable1 addObject: final1];
}
NSUserDefaults *list =[NSUserDefaults standardUserDefaults];
[list setObject:mutable1 forKey:#"favorites"];
[list synchronize];
and i load data like this
NSUserDefaults *prefs1 =[NSUserDefaults standardUserDefaults];
if ( [prefs1 objectForKey:#"favorites"] != nil)
{
mutable1 = [[NSMutableArray alloc] init];
mutable1 = [prefs1 objectForKey:#"favorites"];
and i get the objects! then when it runs the removeallobjects it crashes!

Answer 1

mutable1 = [[NSMutableArray alloc] init];
mutable1 = [prefs1 objectForKey:#"favorites"];
Even though you've declared mutable1 to be an NSMutableArray, you are reassigning it to the object returned by your NSUserDefaults object. This object is apparently an NSArray rather than an NSMutableArray, hence the crash.
You can load your NSMutableArray with the preferences array by doing something like this:
mutable1 = [[NSMutableArray alloc] init];
[mutable1 addObjectsFromArray:[prefs1 objectForKey:#"favorites"]];

Answer 2

The error messages indicate that you're sending the message to an immutable array, which raises an exception. Uncaught exceptions lead to program termination.
How are you creating the array? The most common error that can lead to this is doing something like:
[mutableArray copy]
Even if the thing you're copying is mutable, the copy will be immutable. In that randomly chosen example, use mutableCopy insted.

Answer 3

Somewhere you have set NSMutableArray1 to an instance of NSArray, not NSMutableArray or you declared NSMutableArray1 as a property of type NSArray vs. NSMutableArray.
Also, you should follow Cocoa / Objective-C naming conventions. Namely, class names start with upper case; variables take the form myArray1 (or something more descriptive, preferably).