android - System services not available to Activities before onCreate()

Question

I'm trying to initialize the activityManager like this but it failed . here is the code :

private ActivityManager activityManager = (ActivityManager) getSystemService(ACTIVITY_SERVICE);

Can someone tell me why ??

Answer 1

private建议您尝试初始化成员变量。Activity.getSystemService()需要 a 正确初始化Context，您不能将 aActivity用作Contextuntil onCreate()。

这也在您的问题标题中说明为您得到的例外，IllegalStateException并带有有用的消息"System services not available to Activities before onCreate()"。

要修复它，只需将变量初始化移动到onCreate().