判断activity是否显示在界面上

boolean result = false;
ActivityManager am = (ActivityManager) context
        .getSystemService(Context.ACTIVITY_SERVICE);
ComponentName cn = am.getRunningTasks(2).get(0).topActivity;
if (cn != null) {
    if ("com.android.phone.InCallScreen".equals(cn.getClassName())) {
        result = true;
    }
}
return result;  

需要加入权限:

<uses-permission android:name="android.permission.GET_TASKS" />