Solution to build dynamic forms with Android

Question

I am actually developing an Android application on which I should display dynamic forms based on metadata contained inside JSON documents. Basically the way it works (without the details) is that a JSON document represent the structure of a form:

{
    "fields": [
        {
            "name": "fieldA",
            "type": "STRING",
            "minCharacters": 10,
            "maxCharacters": 100
        },
        {
            "name": "fieldB",
            "type": "INTEGER",
            "min": 10,
            "max": 100
        },
        {
            "name": "fieldC",
            "type": "BOOLEAN_CHECKBOX",
            "defaultValue": true
        }
        ...
    ],
    "name": "Form A"
}

What I'm doing actually when the application receive one of those JSON documents is that it loop through each fields and parse it to the appropriate view (EditText, Checkbox, custom view, etc.), adding a tag to the view (to be able to retrieve it easily) and add the view to a LinearLayout. Here is a pseudo-code of how it is working actually:

//Add form title
linearLayout.addView(new TextView(form.name));
//Add form fields
for(Field field: form.fields) {
    View view;
    switch(field.type){
        case STRING: view = new EditText();
        ...
    }
    view.setTag(field.id);
    linearLayout.addView(view);
}

The issue with this is that with large forms (like >20 fields), it need to inflate lot of views and the UI thread suffer a lot. Another point to take into account is that a single screen may have multiple forms (one after another vertically sorted).

To avoid overloading the UI thread I thought of 2 possible solutions:

1. Using a RecyclerView.
2. Using Litho by Facebook.

But multiple questions comes to me when considering these 2 solutions:

1. Is it a good use case to use Litho? Or using a RecyclerView is enough?
2. What about the state of my views? If I use a Recycling pattern, would I be able to keep the state of each of my fields (even those off-screen) and so being able to save the form without losing data?
3. If I use a Recycling pattern to display one form, how would I handle multiple forms? Can we have nested RecyclerView? Forms need to be displayed one after another like inside a vertical RV but if forms themselves are RV, how should I handle this?

This is more a "good practice" question and giving the right way or one of the right way of achieving my goal than a need of a specific answer with code example, etc.

Thank's in advance for your time.

Answer 1

When architecting for the mobile application I would like to address the following questions:

Is it a good use case to use Litho? Or using a RecyclerView is enough?

1. Are the views are being recycled properly: What does it mean to us is consider, creating 40-50 view per screen and as user moves out of the view, system should not mark all views for GC rather it should be inside some kind archived list and as we require it again we should be able to fetch from it.

   Why do we need to that: GC is the costliest operation which would cause app rendering to be jitter, we try to minimize the GC to called at this point by not clearing the views

   For this I would like to go with litho, justification is here as your requirement seems to have more of variable count of viewtypesreference

   Conclusion: Litho +1, RecyclerView +0

What about the state of my views? If I use a Recycling pattern, would I be able to keep the state of each of my fields (even those off-screen) and so being able to save the form without losing data?

2. Saving EditText content in RecyclerView This is one the component but same logic should be appliced to checkbox or radiobutton as well. or as in state-maintenance for litho is here

   Conclusion: Litho +1, RecyclerView +1 both has specific API's to achieve state maintenance

If I use a Recycling pattern to display one form, how would I handle multiple forms? Can we have nested RecyclerView? Forms need to be displayed one after another like inside a vertical RV but if forms themselves are RV, how should I handle this?

3. This has to be addressed with user experience plus technical capability: As per user behaviour IMHO,I discourage the nested vertical scroll however others were able to achieve it you can easily find on how to in SO. Optimal solution would be to have horizontal scroll within either Andriod's or litho's recycler view as here

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NOTE: If you need to know implementation details, please raise it as separate question, I would be happy to help there

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UPDATE #1:

The issue with this is that with large forms (like >20 fields), it need to inflate lot of views and the UI thread suffer a lot.

UI creation/layout has to be performed at the backend only adding to the view has to be done on UI thread. And litho does it in-built. However same can be achieved native recycler view as well but you have to move off the UI thread and post periodically to UI.

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Answer 2

Ok, you have two separate problems here. One is overwork the UI thread, and the other is to keep the state of your anonymous views. About the first part:

1.-Litho could help you with this. But you have to move all your logic towards litho components instead of android widgets. Since I don't know your codebase, I don't know how hard this can be. A recyclerview would help with view recycling, but that only matters if you are well, using a list.

2.-It could, as long as you have a way to keep a representation of the widget's state that you can pass to the adapter and then back to the view (I'm assuming you generate all the windows by code and then have zero reference to them) and so. It sounds messy, and it is messy, so I won't try it.

3.-You can, but is messy. Best approach in this case would be having horizontal recyclerviews inside a vertical recyclerview. Nesting recyclerviews inside another recyclerview with the same direction creates funny problems, like "Why this cell is not scrolling". I would avoid using the recyclerview as a parent if the view does not need it.

Now, to the solutions:

A) UI Overloading: According to your pseudocode, you aren't inflating stuff. You are creating java objects which happens to be subclasses of View. That's good, because creating objects in a background thread is far easier than inflating (Parsing XML and use it as arguments to generate identical copies of a given resource by invoking constructors) stuff in a background thread. While a LinearLayout context constructor requires an UI thread to be executed, other things, like textviews, don't. So you can create the latter ones inside an asynctask and after you are done generating your whole hierarchy, execute the methods that need the UI thread and add the generated layout to the window. For the view classes that don't support being created as java objects asynchronously, you can have an XML file with just that component, like the linearLayout, and create then asynchronously with the support package asyncLayoutInflater. this solution can be implemented in any codebase and would allow you to make your UI generation completely asynchronous.

B)Keeping track of the view state: Again, I'm assuming your view hierarchy is anonymous. If so, what you need is to generate an interface you can use as a contract to invoke both state saving and state loading from a lifecycle aware component, like the activity. After creating such interface, subclass the widgets and create a subscription/event bus system in each widget that saves/loads the state from the widget every time is triggered. That way, each of of the components on the screen would be able to remember their state while remaining anonymous.

Answer 3

Just use the RecyclerView and create views on runtime (you are not inflating, you are instantiating) Dynamically creating and adding views should not slow the UI thread considerably on mid-range devices. If it does, do investigate for bottlenecks elsewhere

You can perform a simple benchmark by adding/removing/setting text with lots of views dynamically inside a RecyclerView or even a LinearLayout hosted by a ScrollView, and you'll see it goes smooth

Answer 4

Use jetpack composer provided by android

https://developer.android.com/jetpack/compose