Question

在测试一些代码时，我遇到了一个问题。听到我的代码和日志。

(IBAction) DynamicBtnClicked:(id)sender 
{
 NSString *strLog = [[NSString alloc] initWithString:@"SubView Index is..."];
 NSLog(@"initialized strLog address is = %p, retainCount = %d", strLog, [strLog retainCount]);
 if ([self.view.subviews count] > 0) {
     for (int i = 0 ; i < [self.view.subviews count] ; i++) {
         UIView *tmpView = [self.view.subviews objectAtIndex:i];
         strLog = [strLog stringByAppendingFormat:@"%d view`s index = %d, tag = %d", i, i,[tmpView tag]];
         NSLog(@"appended strLog address is = %p, retainCount = %d", strLog, [strLog retainCount]);
     }
 }

 NSLog(@"after appended strLog address is = %p, retainCount = %d", strLog, [strLog retainCount]);    
 UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Alert" message:strLog delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil, nil];
 [alert show];
 [alert release];

 NSLog(@"after using strLog address is = %p, retainCount = %d", strLog, [strLog retainCount]);
 [strLog release];
}

以下是Log

2011-06-03 14:36:11.038 MakeViewUsingCode[3918:40b] initialized strLog address is = 0x45c4, retainCount = 2147483647
2011-06-03 14:36:11.039 MakeViewUsingCode[3918:40b] appended strLog address is = 0x9c028d0, retainCount = 1
2011-06-03 14:36:11.040 MakeViewUsingCode[3918:40b] appended strLog address is = 0x9c021b0, retainCount = 1
2011-06-03 14:36:11.041 MakeViewUsingCode[3918:40b] after appended strLog address is = 0x9c021b0, retainCount = 1
2011-06-03 14:36:11.081 MakeViewUsingCode[3918:40b] after using strLog address is = 0x9c021b0, retainCount = 3
2011-06-03 14:36:11.087 MakeViewUsingCode[3918:40b] *** -[CFString release]: message sent to deallocated instance 0x9c021b0
dlopen(/Developer/Library/Xcode/PrivatePlugIns/DebuggerFoundation.ideplugin/Contents/Resources/DebuggerIntrospectionSupport.dylib, 0x0000000A)
dyld: loaded: /Developer/Library/Xcode/PrivatePlugIns/DebuggerFoundation.ideplugin/Contents/Resources/DebuggerIntrospectionSupport.dylib
Current language:  auto; currently objective-c

我知道，我的代码中存在内存泄漏，但这不是一个真正的问题。（这是故意的。）

真正的问题是，当我运行我的代码时，会发生EXC_BAD_ACCESS运行时错误。

在我的代码中，我向接收者发送一条消息以释放一次但是Log向我显示错误的原因是NSString对象的实例已经被释放！

如果我向接收者发送信息两次发布，第一个位置在哪里？

谁能告诉我它在哪里？

感谢。

Answer 1

当你第一次在循环中将新字符串分配给strlog时，你将丢失对第一个字符串的引用。

NSString *strLog = [[NSString alloc] initWithString:@"SubView Index is..."];
for (int i = 0 ; i < [self.view.subviews count] ; i++) {
     // since you're not releasing the current reference, it's replaced with 
     // the following reference and thus leaked
     strLog = [strLog stringByAppendingFormat:@"%d view`s index = %d, tag = %d", i, i,[tmpView tag]];
}

我相信 stringByAppendingFormat返回一个自动释放的NSString。如果是这种情况，我怀疑你看到的错误是因为，你发布了两次strLog的最后一次引用（创建对象时的隐式自动释放以及方法结束时的显式释放）。 p>

Answer 2

不要太依赖retainCount。它们可能会产生误导。坚持内存管理规则，你会做得很好。这里的问题是这一行，

strLog = [strLog stringByAppendingFormat:@"%d view`s index = %d, tag = %d", i, i,[tmpView tag]];

执行此操作后，strLog指向自动释放的字符串。您尚未声明此字符串的所有权，但仍然在方法结束时将其释放。所以想象它被创造一次并发布两次。那是你的问题。如果您只想将字符串附加到您创建的实例，则必须使用NSMutableString。

NSString发布问题

2 个答案: