Question

我正在确定标签文本,其内容为国家安全局的标签。

出现例外情形时有:

- (void)viewDidLoad{
    [super viewDidLoad];
    NSMutableDictionary *item=[days objectAtIndex:0];
    NSString *title1=[item objectForKey:@"week_day"];
    name1.text=title1;
    [title1 release];

Answer 1

You should not release title1 - you don t own the string returned by -objectForKey: and didn t take ownership by retaining it.
I suggest to read through the Cocoa Memory Management Guide to prevent that in the future.

假设text为retain property: with mutable strings, 您应发号施令,以避免在你的领导下发生改动:

NSString *title1 = [[item objectForKey:@"week_day"] copy];
name1.text = title1;
[title1 release]; // copy means taking ownership, so release

下面是你所颁布的法典可以做到的简单例子:

// entering -viewDidLoad the first time:
NSString *title1=[item objectForKey:@"week_day"];
// lets assume that the strings retain count is 1 here
name1.text=title1;
// setter retains, retain count now 2
[title1 release];
// retain count now 1

// entering -viewDidLoad the second time:
NSString *title1=[item objectForKey:@"week_day"];
// assuming nothing else did retain it, strings retain count is still 1
name1.text=title1;
// you assigned the same object, retain count still 1
[title1 release];
// strings retain count now 0 - will be deallocated :(

Answer 2

Thank you all, now it works fine when i escape the the transition with intermediate variables ,but what i didn t understood why it works for the two "pushing" actions before!!!

name1.text=[[days objectAtIndex:0] objectForKey:@"week_day"];

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