1、以vivoX21手机为例，点亮手机桌面，找到红框所选“口”，长按进入下一步。
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2、红框所选为小锁为锁定按键，点击可锁定后台应用。
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3、点击红框所选小锁，小锁中间多一个圆点出现，显示为锁定状态。
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4、点击下方清理按键，锁定的应用程序无法被清理。
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5、如需解锁后台应用，点击小锁，即可解除锁定。
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