Custom Font to alphanumeric characters only Android.?

Learn custom font to alphanumeric characters only android.? with practical examples, diagrams, and best practices. Covers android, textview, typeface development techniques with visual explanations.
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Applying Custom Fonts to Alphanumeric Characters Only in Android

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Learn how to selectively apply custom fonts to only alphanumeric characters within a TextView in Android, leaving symbols and other characters untouched.

Applying custom fonts in Android is a common practice to enhance the visual appeal of an application. However, there are scenarios where you might want to apply a custom font only to specific character sets, such as alphanumeric characters, while retaining the default system font for symbols, punctuation, or other special characters. This article will guide you through the process of achieving this selective font application in your Android TextViews.

The Challenge of Selective Font Application

By default, when you set a custom Typeface on a TextView, it applies to all characters within that TextView's text. This can sometimes lead to undesirable visual inconsistencies if your custom font doesn't render symbols or special characters as gracefully as the system's default font. The goal is to create a SpannableString that allows us to apply TypefaceSpan only to the alphanumeric portions of the text.

flowchart TD
    A[Input Text] --> B{Iterate Characters}
    B -- Is Alphanumeric? --> C{Apply Custom Font Span}
    B -- Is Not Alphanumeric? --> D{Retain Default Font}
    C --> E[Build SpannableString]
    D --> E
    E --> F[Set to TextView]

Process for selectively applying custom fonts

Implementing a Custom Font Alphanumeric Filter

To achieve selective font application, we'll iterate through the input string, identify alphanumeric characters, and apply a TypefaceSpan to those specific ranges. This requires creating a helper method that takes the original text and the custom Typeface as input and returns a SpannableString.

import android.graphics.Typeface
import android.text.SpannableString
import android.text.Spanned
import android.text.style.TypefaceSpan
import android.widget.TextView

fun TextView.setAlphanumericCustomFont(text: String, customTypeface: Typeface) {
    val spannableString = SpannableString(text)
    for (i in text.indices) {
        val char = text[i]
        if (char.isLetterOrDigit()) {
            spannableString.setSpan(
                TypefaceSpan(customTypeface),
                i,
                i + 1,
                Spanned.SPAN_EXCLUSIVE_EXCLUSIVE
            )
        }
    }
    this.text = spannableString
}

Kotlin extension function for applying custom font to alphanumeric characters

import android.graphics.Typeface;
import android.text.SpannableString;
import android.text.Spanned;
import android.text.style.TypefaceSpan;
import android.widget.TextView;

public class FontUtils {

    public static void setAlphanumericCustomFont(TextView textView, String text, Typeface customTypeface) {
        SpannableString spannableString = new SpannableString(text);
        for (int i = 0; i < text.length(); i++) {
            char c = text.charAt(i);
            if (Character.isLetterOrDigit(c)) {
                spannableString.setSpan(
                        new TypefaceSpan(customTypeface),
                        i,
                        i + 1,
                        Spanned.SPAN_EXCLUSIVE_EXCLUSIVE
                );
            }
        }
        textView.setText(spannableString);
    }
}

Java helper method for applying custom font to alphanumeric characters

Usage Example

Once you have the helper function, using it is straightforward. First, load your custom font, then call the function on your TextView with the desired text and Typeface.

import android.graphics.Typeface
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.TextView

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val myTextView: TextView = findViewById(R.id.myTextView)
        val customFont = Typeface.createFromAsset(assets, "fonts/MyCustomFont.ttf")

        val originalText = "Hello World! 123 @#$ This is a test."
        myTextView.setAlphanumericCustomFont(originalText, customFont)
    }
}

Example of using the Kotlin extension function in an Activity

import android.graphics.Typeface;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        TextView myTextView = findViewById(R.id.myTextView);
        Typeface customFont = Typeface.createFromAsset(getAssets(), "fonts/MyCustomFont.ttf");

        String originalText = "Hello World! 123 @#$ This is a test.";
        FontUtils.setAlphanumericCustomFont(myTextView, originalText, customFont);
    }
}

Example of using the Java helper method in an Activity