Android判斷應用是否已安裝

pageManage = getPackageManager();
        List<PackageInfo> packages = pageManage.getInstalledPackages(0);
                for(int i=0;i<packages.size();i++) {
                        PackageInfo packageInfo = packages.get(i);
                        String appName = packageInfo.applicationInfo.loadLabel(getPackageManager()).toString();
                        String pagName = packageInfo.packageName;
                        if(pagName.equals("com.cric.mobile.manager")){
        image.setBackgroundDrawable(packageInfo.applicationInfo.loadIcon(pageManage));
                Intent intent = pageManage.getLaunchIntentForPackage("com.cric.mobile.manager");
        startActivity(intent);