当控制台出现:

Failed to install ***.apk on device '019417a3': Unable to open sync connection!

java.io.IOException: Unable to open sync connection!

Launch canceled!

或者

Uploading ****.apk onto device '1000b1eda2c2'

Failed to install ****.apk on device '1000b1eda2c2': adb rejected install command with: device offline
com.android.ddmlib.AdbCommandRejectedException: device offline

Launch canceled!

解决方法:

第一种:重启电脑,之后把手机查到电脑上,启动eclipse
第二种:手机-设置-应用程序-开发-usb调试打开再关闭一次
第三种:安装豌豆夹或者360手机精灵在电脑上,用他们连接手机,安装驱动。
第四种:在cmd下Try "adb kill-server" and then "adb start-server"