boolean safe = AntiHijackingUtil.checkActivity(this);
if (safe){


}else {
    Toast.makeText(activity, "某某程式已到後臺執行，請注意資訊保安", Toast.LENGTH_LONG).show();

}

 // 這一套東西 是從誰那弄過來的 我找了好多部落格發現都有 不確定是誰的
public class AntiHijackingUtil {

    public static final String TAG = "AntiHijackingUtil";

    // 白名單列表
 
private static List<String> safePackages;

    static {
        safePackages = new ArrayList<>();
    }

    public static void configSafePackages(List<String> packages) {
        return;
    }
    private static PackageManager pm;
    private List<ApplicationInfo> mlistAppInfo
 
;
    /**
     * 檢測當前Activity是否安全
     */
public static boolean checkActivity(Context context) {
        boolean safe = false;
        pm = context.getPackageManager();
        // 查詢所有已經安裝的應用程式
List<ApplicationInfo> listAppcations = pm.getInstalledApplications(PackageManager.GET_UNINSTALLED_PACKAGES
 
);
        Collections.sort(listAppcations, new ApplicationInfo.DisplayNameComparator(pm));// 排序
List<ApplicationInfo> appInfos = new ArrayList<ApplicationInfo>(); // 儲存過濾查到的AppInfo
        //appInfos.clear();
for (ApplicationInfo app : listAppcations) {//這個排序必須有.
if ((app.flags & ApplicationInfo.FLAG_SYSTEM) != 0) {
                //appInfos.add(getAppInfo(app));
safePackages.add(app.packageName);
            }
        }
        //得到所有的系統程式包名放進白名單裡面.
ActivityManager activityManager =(ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);
        String runningActivityPackageName;
        int sdkVersion;

        try {
            sdkVersion = Integer.valueOf(android.os.Build.VERSION.SDK);
        } catch (NumberFormatException e) {
            sdkVersion = 0;
        }

        if(sdkVersion>=21){//獲取系統api版本號,如果是5x系統就用這個方法獲取當前執行的包名
runningActivityPackageName= getCurrentPkgName(context);
        }
        else runningActivityPackageName=activityManager.getRunningTasks(1).get(0).topActivity.getPackageName();
        //如果是4x及以下,用這個方法.
if(runningActivityPackageName!=null){//有些情況下在5x的手機中可能獲取不到當前執行的包名，所以要非空判斷。
if (runningActivityPackageName.equals(context.getPackageName())) {
                safe = true;
            }

            // 白名單比對
for (String safePack : safePackages) {
                if (safePack.equals(runningActivityPackageName)) {
                    safe = true;
                }
            }
        }

        return safe;
    }



    public static String getCurrentPkgName(Context context) {//5x系統以後利用反射獲取當前棧頂activity的包名.
ActivityManager.RunningAppProcessInfo currentInfo = null;
        Field field = null;
        int START_TASK_TO_FRONT = 2;
        String pkgName = null;

        try {
            field = ActivityManager.RunningAppProcessInfo.class.getDeclaredField("processState");//通過反射獲取程序狀態欄位.
} catch (Exception e) {
            e.printStackTrace();
        }
        ActivityManager am = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);
        List appList = am.getRunningAppProcesses();
        ActivityManager.RunningAppProcessInfo app;
        if (appList!=null){   ／／這個判斷有時候會有問題，瘋狂點選時候會崩潰。
            for (int i=0;i<appList.size();i++){
                //ActivityManager.RunningAppProcessInfo app : appList
app=(ActivityManager.RunningAppProcessInfo) appList.get(i);
                if (app.importance == ActivityManager.RunningAppProcessInfo.IMPORTANCE_FOREGROUND) {//表示前臺執行程序.
Integer state = null;
                    try {
                        state = field.getInt(app);//反射呼叫欄位值的方法,獲取該程序的狀態.
} catch (Exception e) {
                        e.printStackTrace();
                    }
                    if (state != null && state == START_TASK_TO_FRONT) {//根據這個判斷條件從前臺中獲取當前切換的程序物件.
currentInfo = app;
                        break;
                    }
                }
            }
        }

        if (currentInfo != null) {
            pkgName = currentInfo.processName;
        }
        return pkgName;
    }

}