关于xamarin.forms Android创建文件与写文件 （ftp）

现在读写文件在Android原生态应该不在话下了。但是xamarin.forms应该如何用呢

//获取文件的名称含有后缀
string strName = Path.GetFileName(strPath);
strPath = "ftp://" + builder.UserName + ":" + builder.Password + "@" + builder.Host  + strPath;
builder.AllPath = strPath;
//global::Android.OS.Environment.ExternalStorageDirectory.AbsolutePath :得到安卓的根目录
//Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData)：:得到安卓data目录
var path = global::Android.OS.Environment.ExternalStorageDirectory.AbsolutePath + Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData);
//创建文件
System.IO.Directory.CreateDirectory(path);

可是我运行半天在手机上都没有找到我文件。原来是没有权限。如何加权限呢！如下图在安卓项目里有个Properties的文件下有个AndroidManifest.xml的文件。在<application android:label="cardionNet2.Android"></application> 下加

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

这两句就好。

 

之后如何用ftp下载文件呢。

 FtpWebRequest reqFTP = null;//Ftp请求
            FileStream saveStream = null;//Ftp文件流
            Stream ftpStream = null;//Ftp传输流
            FtpWebResponse response = null;//Ftp响应
            try
            {
                var sss = new Uri(builder.Path);
 
                //创建要保存的文件
                saveStream = new FileStream(savePath, FileMode.Create);
                //下载文件设置
                reqFTP = (FtpWebRequest)FtpWebRequest.Create(new Uri(builder.AllPath)); 
                reqFTP.Credentials = new NetworkCredential(builder.UserName, builder.Password);
                reqFTP.Method = WebRequestMethods.Ftp.DownloadFile;
                reqFTP.UseBinary = true;
                //开始请求
                response = (FtpWebResponse)reqFTP.GetResponse();
                //开始下载
                ftpStream = response.GetResponseStream();
                //将下载内容存入文件流
                int bufferSize = 65535;
                int readCount;
                byte[] buffer = new byte[bufferSize];
                readCount = ftpStream.Read(buffer, 0, bufferSize);
                while (readCount > 0)
                {
                    saveStream.Write(buffer, 0, readCount);
                    readCount = ftpStream.Read(buffer, 0, bufferSize);
                }
 }
            catch (WebException webEx)
            {
                throw webEx;
            }
            catch (Exception ex)
            {
                throw ex;
            }
            finally
            {
                //释放资源
                if (ftpStream != null) ftpStream.Close();
                if (saveStream != null) saveStream.Close();
                if (response != null) response.Close();
            }

趋势xamarin的ftp下载文件和c#是一样的关键在于如何在手机上建立文件。