CS193P-向iOS计算器添加取消按钮 [英] CS193P - Adding cancel button to iOS calculator

问题描述

我最近开始在iTunes U上学习斯坦福大学关于iPhone开发的在线课程.

I recently started following the online course on iPhone development from Stanford University on iTunes U.

我现在正在做前几节课的作业.我完成了构建基本计算器的演练，但是现在我正在尝试第一个任务，但似乎无法解决.如下:

I'm trying to do the homework assignments now for the first couple of lectures. I followed through the walkthrough where I built a basic calculator, but now I'm trying the first assignment and I can't seem to work it out. It's a follows:

添加一个"C"按钮以清除所有内容(例如，视图中的显示，模型中的操作数堆栈，控制器中维护的任何状态，等等).确保3 7 C 5导致5出现在显示屏中.您必须将API添加到模型中才能支持此功能.

Add a "C" button that clears everything (for example, the display in your View, the operand stack in your Model, any state you maintain in your Controller, etc.). Make sure 3 7 C 5 results in 5 showing in the display. You will have to add API to your Model to support this feature.

我需要添加什么API?

What API do i need to add?

我尝试过这样的事情:

- (IBAction)CancelPressed {
    self.Display.text = 0;
}

我知道这是错误的.我需要一些指导.在此先谢谢您..很抱歉这个问题很愚蠢..

I know this is wrong. I need some guidance. Thanks in advance..Sorry if the question is stupid..

推荐答案

我也在iTunesU上浏览2011年秋季版.这是我完成此操作的方式.

I am also going through the fall 2011 version on iTunesU. Here is the way I accomplished this.

- (IBAction)clearPressed {
    self.display.text = @"0";
    self.userIsInTheMiddleOfEnteringANumber = NO;
    self.brain = nil;
}

唯一的事情是我实际上不必在模型中添加API.因为控制器有一个CalculatorBrain实例变量，所以我只是把它扔掉了，并且由于我们懒惰地实例化了我们的大脑吸气剂，所以下次我调用吸气剂时，我将得到一个全新的(已经清除).

The only thing is I actually did not have to add API to my model. Because the controller has a CalculatorBrain instance variable I just toss that out, and since we lazily instantiated our brain getter, I'll get a brand new one (already cleared) next time I call the getter.

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