NSString的一点tips

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原文链接：https://yq.aliyun.com/articles/47603

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#python #移动开发 #数据库

本文讨论了在Objective-C中管理NSString实例的正确方法，特别是在从SQLite数据库读取数据并将其添加到NSMutableArray时。文章解释了使用不同字符串创建方法的区别，并提供了一个示例来展示如何正确地分配和释放内存。

When to release a NSString in iPhone

up vote 7 down vote favorite

I have the following method

   -(NSMutableArray *) getPaises {

     NSMutableArray * paises;

     paises = [[NSMutableArray alloc] init];

     while( get new row ) {

      NSString *aPais =  [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 0)];

      [paises addObject:aPais];

     }

     return paises;

    }

I am not releasing the aPais, because if I do it the application crashes. I don't know when or if whether I should release it somewhere after using it and, if so, how do I do it. Just release the NSMutableArray is enough? Or do I have to traverse it and release each object?

And if I don't have to release it, who is the responsible for releasing?

edited Mar 2 '09 at 12:53

andynormancx
3,271 10 26

asked Mar 2 '09 at 12:38

Sacha Fuentes
45 1 4

A note regarding method naming: In Cocoa, a method named “getFoo” returns foo by reference: - (void) getFoo:(out NSMutableArray **)outArray. To be consistent with Cocoa naming conventions, you should name your method simply “paises”. – Peter Hosey Mar 2 '09 at 18:13

feedback

2 Answers

active oldest votes

up vote 6 down vote accepted

As epatel said, you don't need to release that particular string. If you wanted to be more proactive, you could do this instead:

-(NSMutableArray *) getPaises {

    NSMutableArray * paises;

    paises = [[[NSMutableArray alloc] init] autorelease];

    while( get new row ) {

        NSString *aPais =  [[NSString alloc] initWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 0)];

        [paises addObject:aPais];

        [aPais release];

    }

    return paises;
}

In summary:

[[NSString alloc] initWith...] -> You must release or autorelease.
[NSString stringWith...] -> No need to release.

-- Edit: Added autorelease for paises, as you are returning it. When you return an object, always autorelease it if you have alloc&init'd it.

edited Mar 2 '09 at 13:14

answered Mar 2 '09 at 13:01

squelart
2,258 7 17

Thanks a lot. I'm releasing the NSMutableArray manually, but the autorelease is a better option. Gonna change it. – Sacha Fuentes Mar 2 '09 at 14:30

feedback

up vote 4 down vote

stringWithUTF8String: returns an autorelease string which will be released automatically by Cocoa in the next eventloop. But the string is also retained in the array when you do addObject:...so as long as it is in the array it will be retained.

answered Mar 2 '09 at 12:48

epatel
16.8k 8 38 76

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