When I use this method first time it works fine, but when I called it second time I get the error "mutating method sent to immutable object". The problem is at line with "addObject" command.
-(IBAction) save: (id) sender{
NSMutableArray *placesT= [[NSUserDefaults standardUserDefaults] objectForKey:@"placesT"];
if (!placesT) {
placesT=[[[NSMutableArray alloc] init] autorelease];
}
[placesT addObject: [NSString stringWithFormat:@"%@", tagF.text] ];
NSUserDefaults *tUD=[NSUserDefaults standardUserDefaults];
[tUD setObject:placesT forKey:@"placesT"];
[tUD synchronize];
[self dismissModalViewControllerAnimated:YES];
}
As the documentation for NSUserDefaults says: "Values returned from NSUserDefaults are immutable, even if you set a mutable object as the value." Whenever you want to change a collection you get from NSUserDefaults you have to get the immutable version, make a mutableCopy
, modify that, and set it back again.
That is because the object stored in the NSUserDefaults is not the mutableArray but a normal array.
- (IBAction)save:(id)sender {
NSMutableArray *placesT = nil;
NSArray *tempArray = [[NSUserDefaults standardUserDefaults] objectForKey:@"placesT"];
if (tempArray) {
placesT = [tempArray mutableCopy];
} else {
placesT = [[NSMutableArray alloc] init];
}
[placesT addObject:[NSString stringWithFormat:@"%@", tagF.text]];
NSUserDefaults *tUD = [NSUserDefaults standardUserDefaults];
[tUD setObject:placesT forKey:@"placesT"];
[tUD synchronize];
[self dismissModalViewControllerAnimated:YES];
[placesT release];
}
placeT是一个不可更改的数组,可以始终将placesT
始终设置placesT
一个可变对象,也可以使用以下代码。
NSMutableArray *placesT= [[[NSUserDefaults standardUserDefaults] objectForKey:@"placesT"] mutableCopy];
This should work:
-(IBAction) save: (id) sender {
NSMutableArray *placesT= [[NSMutableArray alloc]initWithArray:[[NSUserDefaults standardUserDefaults]
objectForKey:@"placesT"]];
if (!placesT) { placesT=[[[NSMutableArray alloc] init] autorelease]; } [placesT addObject: [NSString stringWithFormat:@"%@", tagF.text] ]; NSUserDefaults *tUD=[NSUserDefaults standardUserDefaults]; [tUD setObject:placesT forKey:@"placesT"]; [tUD synchronize]; [self dismissModalViewControllerAnimated:YES]; }
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