从Java迁移到Kotlin后，Data Binding无法调用单例类方法的问题

Got it, let's break down why your Data Binding setup can't locate the hideNumber method from your StringValidator singleton, and how to fix it.

The Root Cause #

Kotlin's object keyword creates a singleton, but by default, its member methods aren't exposed as static methods to Java code. Since Data Binding is built on Java under the hood, calling StringValidator.hideNumber(...) directly expects a static method—which doesn't exist unless you explicitly mark it as such.

Solution 1: Mark the Method with @JvmStatic #

The simplest fix is to add the @JvmStatic annotation to your hideNumber method. This tells the Kotlin compiler to generate a static version of the method that Java (and Data Binding) can recognize:

object StringValidator {
    // ... other methods/properties

    @JvmStatic
    fun hideNumber(number: String): String {
        return "****" + number.substring(number.length - 4)
    }
}

Now your original Data Binding call will work as expected:

<data>
    <import type="com.your.package.StringValidator" />
</data>

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@{StringValidator.hideNumber(account.number)}" />

(Don't forget to replace com.your.package with the actual package path of StringValidator.)

Solution 2: Use a Singleton Instance Variable in Data Binding #

If you prefer not to use @JvmStatic, you can create a variable in your layout that references the singleton instance, then call the method on that variable:

1. Update your layout's <data> section:

<data>
    <import type="com.your.package.StringValidator" />
    <variable
        name="validator"
        type="StringValidator" />
</data>

2. Assign the singleton instance in your Activity/Fragment:

// In your onCreate (Activity) or onViewCreated (Fragment)
binding.validator = StringValidator

3. Call the method via the variable:

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@{validator.hideNumber(account.number)}" />

Bonus: Handle Null Safety #

To avoid crashes if account.number is null, add a null check in your Data Binding expression:

android:text="@{account.number != null ? StringValidator.hideNumber(account.number) : ``}"

内容的提问来源于stack exchange，提问作者Sigmund