为什么Android Studio中不能引用库如果包含在唯一的build.gradle？

在我的应用我使用的番石榴库。我在的build.gradle 文件中引用它只如下：

In my app I'm using Guava library. I have referenced it in my build.gradle file only as follows:

dependencies {
    compile 'com.google.guava:guava:13.0.1'
 }

我的应用程序改造和运行正常。然而，当我试图从添加番石榴库一个新的东西，然后编译器会抱怨它不能找到类。

My app rebuilds and runs fine. However when I'm trying to add a new something from Guava library then the compiler complains that it can't find the class.

例如：当我写

import com.google.common.base.Preconditions

在我的新文件的编译器说无法解析符号共同的'。

但我的旧文件被重建的罚款。怎么会这样？我必须以项目乱|结构？我特别想列出任何依赖-only-在的build.gradle 。

But my old files are rebuilt fine. How so? Do I have to mess with Project|Structure? I specifically wanted to list any dependencies -only- in build.gradle.