Android判断某个APK是否已安装

关键代码如下：

    private boolean isAppInstalled(String uri) {
        PackageManager pm = getPackageManager();
        boolean installed;
        try {
            pm.getPackageInfo(uri, PackageManager.GET_ACTIVITIES);
            installed = true;
        } catch(PackageManager.NameNotFoundException e) {
            installed = false;
        }
        return installed;
    }