ArgumntNullException未处理 - 请帮助 [英] ArgumntNullException was unhandled - Please Help

问题描述

我正在编写一门编程课程并在其中一项作业中遇到问题。我有3个纹理（bear0，bear1，bear2），我打算随机调用它，基于0-2的随机生成。生成的值应告诉代码使用我的变量currentSprite分配一个
的纹理。但是，当我尝试运行我的程序时，currentSprite显示为具有空值，并且它会破坏程序。如果我在draw函数中用bear0替换currentSprite，程序就可以工作。

Hi, I am doing a coding course and have run into a problem in one of the assignments. I have 3 textures (bear0, bear1, bear2) which I intend to call upon randomly, based on a random generation of 0-2. The value generated should tell the code to assign one of the textures with my variable, currentSprite. however, when I attempt to run my program, currentSprite is showing as having null value, and it breaks the program. If I replace currentSprite with bear0 in the draw function, the program works.

我用粗体突出显示相关代码，但是我把所有我的代码，因为它可能在这一点上很好（我花了几个小时试图解决这个问题）。 

I have highlighted the relevant code in bold, however I put all my code in as it could very well be anything at this point (I have spent hours trying to fix this). 

我的代码（请注意，该程序尚未完成）：

My code (note that the program is not finished):

使用System;

使用Microsoft.Xna.Framework;

using Microsoft.Xna.Framework;

推荐答案

我的猜测是问题就在这一行：

My guess would be that the issue is this line:

 int spriteNumber = rand.Next(0,3);

如果查看 Random.Next 您将看到它接受最小值和最大值设置为0和3.因此spriteNumber
将有1/4的机会被设置为3，即使你只有纹理0,1和2！

If you look at the documentation for Random.Next you will see it accepts a min value and a max value which you are setting to 0 and 3. So there is a 1 in 4 chance that spriteNumber will be set to 3, even though you only have textures 0, 1 and 2!

PS：你可能想要考虑将纹理放入Texture2D数组而不是3个单独的变量。然后你可以从数组中选出值并删除需要做一个大的"if（spriteNumber == 0）等等"。测试：）

PS: You may want to consider putting your textures into a Texture2D array rather than 3 separate variables. Then you can just pick out the value from the array and remove the need to do a big "if (spriteNumber==0) etc etc" test :)

currentSprite = bear[spriteNumber];

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