How to extend ImageView in an Android-Scala app?

Extending ImageView in an Android-Scala App

In Android development, extending existing classes like ImageView allows developers to customize their UI components for specific functionalities. Scala’s interoperability with Java makes it straightforward to work with Android’s core libraries. This article demonstrates how to extend the ImageView class in an Android-Scala application.

Creating a Custom ImageView Class

Defining the Class

package com.example.myapp

import android.content.Context
import android.util.AttributeSet
import android.widget.ImageView

class CustomImageView(context: Context, attrs: AttributeSet) extends ImageView(context, attrs) {
  // Custom logic goes here
}

Adding Custom Attributes

Define custom attributes in the attrs.xml file in your project’s values folder:

<?xml version="1.0" encoding="utf-8"?>
<resources>
  <declare-styleable name="CustomImageView">
    <attr name="imageResource" format="reference" />
    <attr name="borderWidth" format="dimension" />
    <attr name="borderColor" format="color" />
  </declare-styleable>
</resources>

Retrieving Custom Attributes

package com.example.myapp

import android.content.Context
import android.util.AttributeSet
import android.widget.ImageView

class CustomImageView(context: Context, attrs: AttributeSet) extends ImageView(context, attrs) {
  private val typedArray = context.obtainStyledAttributes(attrs, R.styleable.CustomImageView)

  val imageResource = typedArray.getResourceId(R.styleable.CustomImageView_imageResource, 0)
  val borderWidth = typedArray.getDimension(R.styleable.CustomImageView_borderWidth, 0f)
  val borderColor = typedArray.getColor(R.styleable.CustomImageView_borderColor, 0)

  typedArray.recycle()

  // Set image resource
  setImageResource(imageResource)

  // Apply border
  // ... (Code for border customization)

  // Other custom logic
}

Using the Custom ImageView

Now, you can use your custom CustomImageView in your layouts:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <com.example.myapp.CustomImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:imageResource="@drawable/my_image"
        app:borderWidth="2dp"
        app:borderColor="@color/blue" />

</LinearLayout>

Key Points

• Use context.obtainStyledAttributes to get the custom attribute values.
• Recycle the TypedArray using typedArray.recycle() to avoid resource leaks.
• You can extend any Android View class in the same way to create custom UI elements.

Table Comparison

Conclusion

Extending ImageView in your Android-Scala app provides flexibility and a more tailored UI experience. This approach enables you to add custom features and styling for your UI elements, enhancing your application’s functionality and visual appeal.