告诉程序找不到保存数据时该怎么办 NSUserDefaults, iPhone

Tell The Program What To Do When No Save Data Is Found NSUserDefaults, iPhone(告诉程序找不到保存数据时该怎么办 NSUserDefaults, iPhone)

问题描述

I have saved data which was saved using NSUserDefaults. I was under the impression that if there was nothing saved to the key already (first time app is run) it would default to 0. This however doesn't seem to be the case.

Here is what I have:

To save:

- (void)viewWillDisappear:(BOOL)animated
{
[[NSUserDefaults standardUserDefaults] setInteger:setbatteryHealthCalculated     forKey:@"healthValue"];

    [[NSUserDefaults standardUserDefaults] synchronize];

}

To load:

- (void) viewWillAppear:(BOOL)animated
{
NSInteger setbatteryHealthCalculated = [[NSUserDefaults standardUserDefaults]     integerForKey:@"healthValue"];
}

To check for save value:

- (IBAction)check{

    NSInteger setbatteryHealthCalculated = [[NSUserDefaults standardUserDefaults] integerForKey:@"healthValue"];


    if  (setbatteryHealthCalculated = 0) {

                [self performSelector:@selector(displayAlert) withObject:nil];

}
}

if  (setbatteryHealthCalculated = 0) {

Ehm. Should be

if  (setbatteryHealthCalculated == 0)

The comparison operator is == instead of = in C-like languages.

The original code will set setbatteryHealthCalculated to 0 no matter what. Since 0 is false, the if branch will never be executed and no alerts would be shown.

Also, the original code has unbalanced braces.

BTW, is setbatteryHealthCalculated an ivar? If yes, remove the NSInteger before it. Otherwise you're declaring a local variable which shadows the ivar.

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