Question

我正在设置带有NSMutableString_s内容的标签文本，它们是NSMutableDictionray的对象......当我加载页面两次时所有工作正常的问题（所以我推，我弹出后... 。）并且在第三次推送时程序无法读取NSMutableDictionary..so的NSMutableString_s之一的内容，当它转到设置UILabel的值的步骤时，它没有找到值... < / p>

出现异常的代码：

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

Answer 1

您不应该发布title1 - 您不拥有-objectForKey:返回的字符串，并且没有保留所有权。
我建议您仔细阅读Cocoa Memory Management Guide以防止将来发生这种情况。

假设text是retain属性：使用可变字符串，您应该分配字符串的副本以避免在您下面更改它们：

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

以下是您的代码发布时可能发生的事情的简化示例：

// 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

谢谢大家，现在，当我用中间变量逃避转换时，它工作正常，但我不明白为什么它适用于之前的两个“推动”动作!!!

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

NSMutableDictionary不能有“时间”来读取对象（NSMutableString s）

2 个答案: