NSUndoManager是否保留其参数？ [英] Does NSUndoManager retain its arguments?

问题描述

以下是用于启用Aaron Hillegas对OS X的可可编程的撤消的代码：

The following is code for enabling undo from the book cocoa programming for OS X by Aaron Hillegas :

-(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];
}

在移除员工时，我们将一个命令推送到撤销堆栈， employee into数组。但是，当调用撤消时，是什么保证p不会被释放？

While removing an employee , we push a command onto the undo stack to reinsert that employee into the array . But what guarantee is there that p wont have been released when the undo is invoked ?

推荐答案

NSInvocation是由[[undo prepareWithInvocationTarget：self] insertObject：p inEmployeesAtIndex：index]创建的

'p' will get retained when the NSInvocation is created by "[[undo prepareWithInvocationTarget:self] insertObject:p inEmployeesAtIndex:index]"

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