launch appium时出现以下错误：

 Launching Appium server with command: D:\Program Files\Appium\node.exe lib\server\main.js --address 127.0.0.1 --port 4273 --pre-launch --platform-name Android --platform-version 19 --automation-name Appium --device-name "127.0.0.1:62001" --log-no-color

> info: [debug] Starting Appium in pre-launch mode

> info: Pre-launching app

> info: [debug] No appActivity desired capability or server param. Parsing from apk.

> info: [debug] No appPackage desired capability or server param. Parsing from apk.

> error: No app set; either start appium with --app or pass in an 'app' value in desired capabilities, or set androidPackage to launch pre-existing app on device

> info: [debug] Got configuration error, not starting session

> info: [debug] Cleaning up appium session

> error: Could not pre-launch appium: Error: No app set; either start appium with --app or pass in an 'app' value in desired capabilities, or set androidPackage to launch pre-existing app on device

> 

尝试多次  问题依然存在   不是如何是好啊   求老师支招