問題如下：
[2018-01-15 11:46:26 - Dex Loader] Failed to load F:\Android-SDK\build-tools\26.0.1\lib\dx.jar
[2018-01-15 11:46:26 - HelloAndroid] Unknown error: Unable to build: the file dx.jar was not loaded from the SDK folder![2018-01-15 11:49:09 - Dex Loader] Failed to load F:\Android-SDK\build-tools\26.0.1\lib\dx.jar
[2018-01-15 11:49:09 - HelloAndroid] Unknown error: Unable to build: the file dx.jar was not loaded from the SDK folder!
[2018-01-15 11:49:40 - Dex Loader] Failed to load F:\Android-SDK\build-tools\26.0.1\lib\dx.jar
[2018-01-15 11:49:40 - HelloAndroid] Unknown error: Unable to build: the file dx.jar was not loaded from the SDK folder!
[2018-01-15 11:50:15 - Dex Loader] Failed to load F:\Android-SDK\build-tools\26.0.1\lib\dx.jar
[2018-01-15 11:50:15 - HelloAndroid] Unknown error: Unable to build: the file dx.jar was not loaded from the SDK folder!
[2018-01-15 11:55:34 - Dex Loader] Failed to load F:\Android-SDK\build-tools\26.0.1\lib\dx.jar
[2018-01-15 11:55:34 - HelloAndroid] Unknown error: Unable to build: the file dx.jar was not loaded from the SDK folder!
[2018-01-15 11:56:50 - Dex Loader] Failed to load F:\Android-SDK\build-tools\26.0.1\lib\dx.jar
[2018-01-15 11:56:50 - HelloAndroid] Unknown error: Unable to build: the file dx.jar was not loaded from the SDK folder!
都說找不到26.0.1這個版本的sdk裏lib文件夾下的dx.jar文件。
解決辦法：把早期版本的sdk（如25.0.2）的lib文件夾裏的dx.jar文件粘貼並替換掉他報錯中的這個出錯的dx.jar