android studio，sdk的问题。

你好



我非常初学我的第一个应用程序。



我安装了android studio试图做一些简单的应用程序



当我尝试运行该程序时，我收到一条消息，告诉我必须为android工作室选择sdk即使我从SDK Manager安装了API20所需的所有软件包。



如果你看一下我的android工作室你会看到渲染布局的null图标。



在java代码中，当我尝试导入像android这样的东西时，它都是红色的。*****



希望我的问题很明确，对不起我的英语。



谢谢大家。

Hello

I am very beginner with android doing my very first application.

I installed android studio trying to do some simple app

When I try to run the program I get a message telling me that I have to choose the sdk for the android studio even though I installed all the packages necessary for the API20 from the "SDK Manager".

If you take a look at my android studio you see "null" with the rendering layout icon.

And in the java code it's all red when I try to import anything like android.*****

Hope my question is clear, sorry for my English.

Thank you all.