无法使用minSdk = 21构建项目

Question

我成功地使用最多20秒的最小sdks构建项目,但是当我尝试构建时:

minSdkVersion 21
targetSdkVersion 21

我收到一个错误:

:project:preDexDebug
no classfiles specified

FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':project:preDexDebug'.
> com.android.ide.common.internal.LoggedErrorException: Failed to run command:
/Users/user/android-sdk-macosx/build-tools/21.1.1/dx -JXmx2g --dex --multi-dex --output /Users/user/Project-Android/project/build/intermediates/pre-dexed/debug/tween-engine-api-sources-a613effab3e9735b093029491b18c5c4872bdf88.jar /Users/user/Project-Android/project/build/intermediates/exploded-aar/android-ui-client.gdxlibrary/android/unspecified/libs/tween-engine-api-sources.jar
Error Code:
1
Output:
no classfiles specified

我在应用程序的某些地方使用libgdx.

然后安装对话框出现,如果我选择一个设备,我会收到另一个错误:

Target device: genymotion-google_nexus_6___5_0_0___api_21___1440x2560-192.168.56.103:5555
Uploading file
    local path: /Users/user/Project-Android/project/build/outputs/apk/project-debug.apk
remote path: /data/local/tmp/com.ui.client.debug
I/O Error: /Users/user/Project-Android/project/build/outputs/apk/project-debug.apk (No such file or directory)

然后IDE对话框出现错误消息:

Failed to complete Gradle execution.

Cause: 

(原因之后只是空的空间)

Answer 1

我有完全相同的问题。使用 --debug 选项运行 gradle 后，发现 gradle 无法处理其中没有类文件的 jar 文件（*-javadoc.jar）。

从 /libs 文件夹中删除文件解决了该问题。