How to retrieve my Gmail messages using Gmail API?

Question

What I want to achieve:

---

I\'m using the Gmail API and basically I would like to connect to my GMail account to read my emails, of INBOX categ

Answer 1

Currently for some reason or another many of the properties are coming back null from any of the requests. We can still get around that if we have a list of the email ids. We then can use these email ids to send out another request to retrieve further details: from, date, subject, and body. @DalmTo was on the right track as well, but not close enough about the headers as it has changed recently which will require a few more requests.

private async Task getEmails()
{
    try
    {
        UserCredential credential;
        using (var stream = new FileStream("client_secrets.json", FileMode.Open, FileAccess.Read))
        {
            credential = await GoogleWebAuthorizationBroker.AuthorizeAsync(
                GoogleClientSecrets.Load(stream).Secrets,
                // This OAuth 2.0 access scope allows for read-only access to the authenticated 
                // user's account, but not other types of account access.
                new[] { GmailService.Scope.GmailReadonly, GmailService.Scope.MailGoogleCom, GmailService.Scope.GmailModify },
                "NAME OF ACCOUNT NOT EMAIL ADDRESS",
                CancellationToken.None,
                new FileDataStore(this.GetType().ToString())
            );
        }

        var gmailService = new GmailService(new BaseClientService.Initializer()
        {
            HttpClientInitializer = credential,
            ApplicationName = this.GetType().ToString()
        });

        var emailListRequest = gmailService.Users.Messages.List("EMAILADDRESSHERE");
        emailListRequest.LabelIds = "INBOX";
        emailListRequest.IncludeSpamTrash = false;
        //emailListRequest.Q = "is:unread"; // This was added because I only wanted unread emails...

        // Get our emails
        var emailListResponse = await emailListRequest.ExecuteAsync();

        if (emailListResponse != null && emailListResponse.Messages != null)
        {
            // Loop through each email and get what fields you want...
            foreach (var email in emailListResponse.Messages)
            {
                var emailInfoRequest = gmailService.Users.Messages.Get("EMAIL ADDRESS HERE", email.Id);
                // Make another request for that email id...
                var emailInfoResponse = await emailInfoRequest.ExecuteAsync();

                if (emailInfoResponse != null)
                {
                    String from = "";
                    String date = "";
                    String subject = "";
                    String body = "";
                    // Loop through the headers and get the fields we need...
                    foreach (var mParts in emailInfoResponse.Payload.Headers)
                    {
                        if (mParts.Name == "Date")
                        {
                            date = mParts.Value; 
                        }
                        else if(mParts.Name == "From" )
                        {
                            from = mParts.Value;
                        }
                        else if (mParts.Name == "Subject")
                        {
                            subject = mParts.Value;
                        }

                        if (date != "" && from != "")
                        {
                            if (emailInfoResponse.Payload.Parts == null && emailInfoResponse.Payload.Body != null)
                            {
                                body = emailInfoResponse.Payload.Body.Data;
                            }
                            else
                            {
                                body = getNestedParts(emailInfoResponse.Payload.Parts, "");
                            }
                            // Need to replace some characters as the data for the email's body is base64
                            String codedBody = body.Replace("-", "+");
                            codedBody = codedBody.Replace("_", "/");
                            byte[] data = Convert.FromBase64String(codedBody);
                            body = Encoding.UTF8.GetString(data);                               

                            // Now you have the data you want...                         
                        }
                    }
                }                    
            }
        }           
    }
    catch (Exception)
    {
        MessageBox.Show("Failed to get messages!", "Failed Messages!", MessageBoxButtons.OK); 
    }
}

static String getNestedParts(IList part, string curr)
{
    string str = curr;
    if (part == null)
    {
        return str;
    }
    else
    {
        foreach (var parts in part)
        {
            if (parts.Parts  == null)
            {
                if (parts.Body != null && parts.Body.Data != null)
                {
                    str += parts.Body.Data;
                }
            }
            else
            {
                return getNestedParts(parts.Parts, str);
            }
        }

        return str;
    }        
}

Currently, this method will retrieve all email ids and for each email id get the subject,from, date and body of each email. There are comments throughout the method. If there is something you do not understand, please let me know. On another note: this was tested again before posting this as an answer.