“Android library projects cannot be launched”?

Question

Now I am totally confused by this error message: Android library projects cannot be launched.

I carefully checked the build path and library, every

Answer 1

From Android's Developer Documentation on Managing Projects from Eclipse with ADT:

Setting up a Library Project

Next, set the project's Properties to indicate that it is a library project:

1. In the Package Explorer, right-click the library project and select Properties.
2. In the Properties window, select the "Android" properties group at left and locate the Library properties at right.
3. Select the "is Library" checkbox and click Apply.
4. Click OK to close the Properties window.

So, open your project properties, un-select the "Is Library" checkbox, and click Apply to make your project a normal Android project (not a library project).