cocoa - NSUndoManager 是否保留其参数？

Question

以下是 Aaron Hillegas 的书 cocoa programming for OS X 中启用撤消的代码：

-(void)removeObjectFromEmployeesAtIndex:(NSUInteger)index
{
Person *p = [employees objectAtIndex:index];
NSLog(@"removing %@ from %@", p, employees);
// Add the inverse of this operation to the undo stack 
NSUndoManager *undo = [self undoManager]; [[undo prepareWithInvocationTarget:self]  insertObject:p inEmployeesAtIndex:index]; 

if (![undo isUndoing]) { 
  [undo setActionName:@"Remove Person"];
} 
[employees removeObjectAtIndex:index];
}

在删除员工时，我们将命令推送到撤消堆栈以将该员工重新插入到数组中。但是有什么保证 p 在调用 undo 时不会被释放？

Answer 1

当 NSInvocation 由 "[[undo prepareWithInvocationTarget:self] insertObject:p inEmployeesAtIndex:index]" 创建时，'p' 将被保留