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Extremely easy to do, but extremely easy to mess up. I’m assuming with this post you have already configured Azure Mobile Services with your certificates. If not, there are plenty of tutorials around which can help you through the process. (I personally like this one for APNS.)

The classic Mobile Services examples all involve the Todo List app, which expect you to be using the full Mobile Services backend. It’s certainly slick if you can, but what if you only need the push notification capabilities? This is the problem I was trying to solve. The data for my mobile application is already managed elsewhere, I only need Mobile Services to manage the push subscriptions for my end users. The Javascript API portion of Mobile Services will be called from my backend and by some other applications using C# to generate the push notifications. It’s maybe not a common scenario, but it’s certainly there to allow you to do it. No amount of Google/Bing attempts landed me on a nice tutorial which satisfied my questions, so I’ll do my best.

Go to the API tab in your mobile service in the portal, and either click on the Create option at the bottom or click the big message in the center of the screen. Enter the name you want for the API, I choose Godzilla. (There was a marathon on El Rey last weekend, so I have Godzilla on the brain still.) Set the app permissions appropriately for your API, I’ll to stick with “Anybody with the Application Key” for the example and click the Checkmark button.

Screenshot 2015-07-09 15.39.09

Once it’s done creating the API, click on it to view the code. You’ll have the starter API with a Post and a Get.

There’s no need for the Get, so delete it. The Post has a hint of what you need to use on the third line of comments, “var push =…”. Let’s uncomment that line so we can use it to generate the push. (I’m only going to write the code to send pushes to iOS (APNS) to keep the example nice and simple, the code for Android should be fairly trivial to add.) After the line with “var push = …”, paste in the following code over the remaining body of Post.

push.apns.send("atombomb", {
        alert: request.body.msg       
    },{ 
        success: function(result){
            //console.log("Godzilla push success");
       }, error: function(error){
           console.log("Godzilla push failed, error: " + error);
       }
    });
    response.send(statusCodes.OK, "{msg: 'Push executed, check log for results'}");

So what is this doing? It will push a notification to only the users subscribed to the “atombomb” tag. If you want to push to all users who have allowed push notifications for your app, change that parameter to null, without quotes around null. The next parameter is the JSON content which will be the contents of the push notification. (Here’s a great reference for more options you can put in it.) You see many other examples where they only use the payload property, which is certainly nice if you need to send some data with the push, but won’t actually pop a message on the user’s device. Alert is what you need to pop a message up, and the contents of the Alert parameter get displayed on the top of the user’s screen when it is received.

Quick side tangent. If you only provide the Payload property, as I did at first, it’s hugely confusing why there isn’t a notification popping up on the device. The portal will show the push succeeds, but nothing shows up on the device. The reference link above was the light bulb moment when I realized what I had done wrong. If there is no alert property as part of the content parameter, the user will not be notified in any way. You only want to use Payload by itself when you want to push an update in the background, without the user being prompted. You can certainly use both Alert and Payload at the same time, however.

On my alert parameter, you can see I’m actually sending in the content as part of the body of the API call. If you know your push message will always be the same, you can change this out for a string right there, but I think a parameter from the body makes for a better real world example. The final parameter contains the success and error functions, which are really useful for debugging. They will write to the mobile service log using console.log, which I’ll get to next. So here’s the final result:

Screenshot 2015-07-09 16.22.22

I also edited the response message, but you can leave it as the default if you like. Now click the save button at the bottom to save your changes. If you want to check the logs once you have called your new API, click the back arrow after saving and it’s the last option in the top menu. You may need to uncomment the body of the success function to get anything to appear there, if it all works right away.

Screenshot 2015-07-09 16.24.33

So now we need to call our API. This is when Mobile Services really flexes its muscles, it’s so incredibly simple. I’ve got a fairly reusable method for this which lets me pass in the API I want to call, and the message I want to send. So when invoking the method below, I use the parameters “Godzilla” for Api and “I knew that tuna-eating monster was useless!” for Message. If you’ve swapped out the message in the body for a string as I mentioned earlier, it gets even easier as you can then remove two lines which deal with the body variable.

public async Task SendPushNotification(string Api, string Message)
        {
            JObject body = new JObject();
            body.Add("msg", Message);
	    MobileServiceClient client = new MobileServiceClient(appUrl, appKey);
            return await client.InvokeApiAsync(Api, body);
        }

You can go much further with that method if you want, such as passing in your own custom object rather than using a JObject. If you’re looking to do something like that, I would recommend reading “Custom API in Mobile Services,” it goes nicely into a scenario like that, and includes a little bit on handling authenticated users.