Android Dynamic Views: Is Runtime XML Parsing Possible?

• ⚠️ Android does not support loading raw XML layout strings at runtime using LayoutInflater.
• 🧠 Creating UI in code is the safest way that works well for building UIs that change or grow.
• 🌐 WebView allows showing HTML that changes but has downsides for performance and security.
• 📦 Jetpack Compose offers a new, clear way to build UIs that can change completely while the app is running, instead of using XML layouts.
• 📉 Performance and security can get much worse when handling UI content that changes and isn't checked first.

When building modern Android apps, being able to change how the UI looks is sometimes needed. This might be to support layouts users set up, UIs sent from a server, or behavior that changes for testing and making things personal. Developers often ask if they can get XML layouts and show them while the app is running. Being able to read XML layout strings would offer big UI flexibility. But the standard Android UI system is not made to take XML code while the app is running. This article explains how Android UI is made, why you can't parse XML when the app is running, and what else you can do to make UIs that change in apps today.

The Fixed Nature of Android Layout Inflation

Android layouts made with XML are a core part of making UIs on the platform. These layout files, usually in the /res/layout folder, are read and put together when you build the app using the Android Asset Packaging Tool (AAPT). After they are built, you use the R.layout names created automatically in your Kotlin or Java code to find them. When the app is running, Android shows these layouts using:

val view = LayoutInflater.from(context).inflate(R.layout.activity_main, parent, false)

But this system has a key limit: the layout file must be built beforehand and packaged with your app file (APK). Android does not read raw XML text saved somewhere else (like from your server or text a user typed).

This means you cannot use LayoutInflater to make UI pieces from raw XML you get when the app is running. It only works with XML files that were processed already and linked to how your app was built.

📚 The layout XML files are built into View resources. You then get to them when the app is running using the names in R.layout.

Can You Parse XML or HTML While the App is Running?

XML Parsing While the App is Running: Not Built-in

Android doesn't provide a way to load XML layouts defined as simple text strings when the app is running. Lots of developers find this limit when they try to make layouts that can change more easily or are based on data. The main reason for this limit comes from how Android handles performance:

• When you build the app, AAPT works through all the .xml layout files. It turns them into .flat binary files that are fast to use.
• When the app is running, LayoutInflater only works with these resources that were built beforehand.

If you try to parse XML using LayoutInflater from just any string that is not part of your app's APK, you will get an error like this:

java.lang.IllegalArgumentException: Binary XML file line #1: Error inflating class ...

Parsing HTML vs XML

Android doesn't let you load XML layouts while the app is running. But it does offer some built-in support for showing HTML content in some parts like TextView (using Html.fromHtml()) or showing full HTML inside WebView. This is HTML, though, not the layout XML Android uses. You cannot make UI pieces like LinearLayout, TextView, or ConstraintLayout by writing HTML.

Looking at Other Options: Is It Possible?

In theory, you could read and show simple UI pieces using something like XmlPullParser. This can read simple XML text strings while the app is running. People would then make view objects themselves in code, matching XML tags to the right Android View classes.

Example:

val parser = Xml.newPullParser()
parser.setInput(StringReader(yourXmlString))
// Step through and manually map nodes like <TextView> or <Button> to Android Views

But this takes a lot of work. It means carefully handling details like attributes, styles, and how views are nested. It also doesn't work well with Android's system for managing resources and often gives results you can't count on, especially when dealing with layouts that are complicated.

Because of these problems, this way of doing things is often too much trouble to keep up unless your app has very specific needs for showing content (like apps for editing visuals or building pages).

Using WebView for UI Made with HTML

For content that changes and comes from a server or another source, WebView is an easy choice. It can show HTML while the app is running. WebView works like a small browser inside your app. It can load websites from far away or HTML content that is right there.

Example:

val webView = WebView(context)
webView.loadData(htmlString, "text/html", "UTF-8")

Good Points

• ✅ Easy to show rich content from a server
• ✅ Works with HTML, CSS, and JavaScript
• ✅ No need to set up layouts ahead of time

Bad Points

• ❌ Uses a lot of resources
• ❌ Doesn't fit smoothly with Android's standard UI
• ❌ Can have security risks if you load JavaScript you don't trust
• ❌ Works poorly compared to standard views

Unless your app really needs to show HTML content (like an app to view documents or content put inside), it's best not to use WebView just to show UI that could be done with standard views.

📚 WebView lets apps show web content, including HTML and JavaScript.

Making Views with Code: A Better Way

Since you can't parse XML when the app is running, the best way to make UIs that change on Android is by writing code. Building views with code lets you use all the settings and freedom the platform gives you, and you don't need layout files.

Here is a quick example:

val button = Button(context).apply {
    text = "Submit"
    setBackgroundColor(Color.parseColor("#6200EE"))
    setTextColor(Color.WHITE)
    setPadding(24, 16, 24, 16)
}
linearLayout.addView(button)

This method works well as your app grows. It lets you change the UI based on what the user does, what you get from the internet, or the app's status. You can:

• Change layouts for different screen sizes or if the screen is sideways
• Put in or take out views based on feature settings
• Make small parts of the UI quickly for special content sections

Making views with code also works with standard Android tools like ViewModels, LiveData, and navigation parts.

Other Tools and Ways to Build UI with Code

To make building UI with code simpler, the Android world has several free libraries and systems:

Jetpack Compose

Jetpack Compose is Android's newer UI toolkit. It uses Kotlin code to describe how the UI looks, replacing XML layouts. It allows:

• Full UI changes while the app runs
• Checks for types and helps with writing code
• Works well for bigger apps with tools to manage status
• Has built-in support from Android development tools

Example:

@Composable
fun DynamicButton(text: String) {
    Button(onClick = { /* Do something */ }) {
        Text(text)
    }
}

Jetpack Compose is great when you need the UI to change because the whole layout is made and remade while the app is running whenever the status changes.

Engines that Turn JSON into Views

Some big apps use their own view systems. These systems get a description of the layout in JSON format from the server and build the views right away.

Example JSON:

{
  "view": "Button",
  "attributes": {
    "text": "Start Now",
    "background": "#00BCD4"
  }
}

This information can be read into a list and matched to Android Views using code. Even though Android doesn't offer this built-in, systems like this are becoming common in apps used by many people.

Making Layouts from JSON: A Standard Way

JSON is a good format for sending layout details over APIs because it's small and easy to read. UIs that are set up by the server often use structures like this:

[
  {
    "type": "text",
    "value": "Welcome to our survey",
    "style": {
      "fontSize": 20,
      "textColor": "#333333"
    }
  },
  {
    "type": "button",
    "value": "Start",
    "action": "start_survey"
  }
]

Simple matching logic:

when (json["type"]) {
    "text" -> {
        val textView = TextView(context)
        textView.text = json["value"]
        // apply styles
    }
    "button" -> {
        val button = Button(context)
        button.text = json["value"]
        button.setOnClickListener { performAction(json["action"]) }
    }
}

This way of doing things is:

• ✨ Very easy to change
• 🔧 Simple to check and fix problems
• 🔒 Safe, if you clean the data
• 📊 Works well with different Android versions

When Not to Make UI with Code

Making Android views that change with code is a strong ability, but you should not use it too much. You might want to avoid it in these cases:

• Your UI doesn't change based on the user or situation
• Layouts stay the same and are easy to handle using .xml files
• Your team uses UI Designers or tools linked to XML layouts
• How fast the app runs is very important

When you can, stick with layouts defined without code that changes. They work better with tools, have fewer unexpected issues, show up faster, and are easier to keep updated.

What's Coming for Android: Jetpack Compose

Google is slowly moving Android UI building towards Jetpack Compose. This is a UI toolkit made completely with Kotlin code, which describes the UI. Compose means you don't need XML at all:

• No need for LayoutInflater
• No findViewById
• UIs are described by functions and update when their state changes

For example:

@Composable
fun SignupScreen(viewModel: SignupViewModel) {
    val state = viewModel.uiState.collectAsState()

    Column {
        Text(state.value.title)
        Button(onClick = { viewModel.onSignupClick() }) {
            Text("Join Now")
        }
    }
}

This way of working not only handles content that changes but makes it easy to do. You can easily add settings from a server, turn features on or off, and do tests where different users see different things by changing the UI based on state.

Things to Think About for Security When UI Changes

Taking content from any source you haven't checked or don't trust when the app is running makes your app easier to attack. Some main risks are:

• 🔓 WebView can be used to attack with XSS if JavaScript is on or the content isn't kept separate
• 🛑 Badly made XML or JSON can make the parts that read them stop working or cause problems showing things
• ⚠️ How things are shown can be misused to get out parts of your app's inner workings if not kept safe

How to make things safer:

• Check everything you get (for example, check JSON matches a set pattern)
• Turn off JavaScript you don't need or CSS written right into the HTML in WebViews
• Don't put text that users control into HTML

You can also hide parts that show content that changes behind feature switches. This lets you test them out slowly to stop big problems if something goes wrong.

How Performance is Affected

Logic that makes the UI change might cost you in speed:

It's very smart to test your UI with the kind of data amounts and layout difficulty you expect in the real world before deciding how you will make views that change.

Quick Look and What to Do

Android doesn't allow parsing XML while the app is running using LayoutInflater. If you want to make UI based on data or that changes, it's better to focus on:

• ✅ Making Views with Kotlin or Java code
• ✅ Setting up layouts from the server using JSON structures
• ✅ Jetpack Compose for new, easy-to-use UI that works well while the app is running
• 🚫 Don't use WebView for regular UI unless the content requires it
• 🧪 Always check and make safe the ways you show content that changes

Views that change are helpful when your app needs to show content from a server or create personalized views. But with that power comes more things to handle.

References

• Android Developers. (n.d.). Build UI with Layout Editor. Retrieved from https://developer.android.com/studio/write/layout-editor
• Android Developers. (n.d.). WebView. Retrieved from https://developer.android.com/reference/android/webkit/WebView
• Stack Overflow contributor response (n.d.). Raw XML cannot be inflated via LayoutInflater unless precompiled and included in the project resources (paraphrased)