检测应用程序是否已经安装

private boolean isAvilible( Context context, String packageName )
    {
        final PackageManager packageManager = context.getPackageManager();
        // 获取所有已安装程序的包信息
        List<PackageInfo> pinfo = packageManager.getInstalledPackages(0);
        for ( int i = 0; i < pinfo.size(); i++ )
        {
            if(pinfo.get(i).packageName.equalsIgnoreCase(packageName))
                return true;
        }
        return false;
    }