The following answer: "Is application running in background", summarizes solutions available for background/foreground checking.
Note:
Previously this answer suggested to use ActivityManager.getRunningAppProcesses(), however that method appeared to be not completely reliable and its usage is discouraged. Check the link above for the details.
与恶龙缠斗过久,自身亦成为恶龙；凝视深渊过久,深渊将回以凝视…
