将字符串附加到 NSMutableString
现在已经研究了一会儿，但不明白为什么这段简单的代码会抛出错误。为简洁起见缩短：
NSMutableString *output;
...
@property (nonatomic, retain) NSMutableString *output;
...
@synthesize output;
...
// logs "output start" as expected
output = [NSMutableString stringWithCapacity:0];
[output appendString:@"output start"];
NSLog(@"%@", output);
...
// error happens here
// this is later on in a different method
[output appendString:@"doing roll for player"];
有人能发现我的错误吗？
Been looking at this for a bit now and not understanding why this simple bit of code is throwing an error. Shortened for brevity:
NSMutableString *output;
...
@property (nonatomic, retain) NSMutableString *output;
...
@synthesize output;
...
// logs "output start" as expected
output = [NSMutableString stringWithCapacity:0];
[output appendString:@"output start"];
NSLog(@"%@", output);
...
// error happens here
// this is later on in a different method
[output appendString:@"doing roll for player"];
Can anyone spot my mistake?
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行更改
将
output = [NSMutableString stringWithString:@"output start"]为
[self setOutput:[NSMutableString stringWithString:@"output start"]]（或
self.output = ...（如果您喜欢这种表示法）。尽管您已经声明了一个属性，但您没有使用 setter，因此您没有保留该字符串。
Change the line
output = [NSMutableString stringWithString:@"output start"]to
[self setOutput:[NSMutableString stringWithString:@"output start"]](or
self.output = ...if you prefer that notation).Although you have declared a property, you are not using the setter, so you are not retaining the string.
事实上，解决方案确实与保留有关，正如用户不变所指出的那样。类方法：
返回一个
autoreleaseNSMutableString。当分配给我的输出属性时——看起来，即使有保留标志——它也没有保留它。解决方案是自己分配它而不是自动释放：然后保留就起作用了。任何关于原因的解释都将非常受欢迎。
编辑
找出原因。我直接访问实例变量，而不是通过我合成的 getter/setter。有关更多信息，请访问我的博客。
The solution did in fact have to do with retention, as indicated by user invariant. The class method:
returns an
autoreleaseNSMutableString. When assigned to my output property -- seemingly, even with the retain flag -- it did not retain it. The solution was to alloc it myself and not autorelease:Then the retain worked. Any explanation as to why would be very welcome.
Edit
Figured out why. I was accessing the instance vars directly instead of through the getter/setter that I synthesized. More info on my blog.