How to use the custom font inside the entire app. This example is for how to use custom font for all textviews inside the app.

customFont.txt

// add fonts inside the *assets/fonts* folder
// create a class named customTextView.java


public class customTextView extends TextView {
	private static final String SCHEMA = "http://schemas.android.com/apk/res/android";

	public customTextView(Context context, AttributeSet attrs, int defStyle) {
		super(context, attrs, defStyle);
		getStyle(attrs, context);
	}

	public customTextView(Context context, AttributeSet attrs) {
        super(context, attrs);
        getStyle(attrs, context);
    }

	public customTextView(Context context) {
        super(context);
        getStyle(null, context);
    }
	
	// get the style of the textview and apply the font accordingly.
	private void getStyle(AttributeSet attr, Context context){
		int textStyle = 0;
		Typeface tf = null;
		if(attr!=null){
			textStyle = attr.getAttributeIntValue(SCHEMA, "textStyle", 0);
		}
		switch (textStyle) {
		case Typeface.NORMAL:
			// textstyle normal case and set the normal custom font. 
			tf = Typeface.createFromAsset(getContext().getAssets(), "fonts/normal.ttf");
			break;
		case Typeface.BOLD:
			// textstyle bold case and set the bold custom font. 
			tf = Typeface.createFromAsset(getContext().getAssets(), "fonts/bold.ttf");
			break;
		case Typeface.ITALIC:
			// textstyle italic case and set the italic custom font. 
			tf = Typeface.createFromAsset(getContext().getAssets(), "fonts/italic.ttf");
			break;
		case Typeface.BOLD_ITALIC:
			// textstyle bold_italic case and set the bold_italic custom font. 
			tf = Typeface.createFromAsset(getContext().getAssets(), "fonts/bold_italic.ttf");
			break;
		default:
			break;
		}
		// method to set the typeface
		setTypeface(tf);
	}
}

//**************XML CODE****************

1. Normal font
<com.example.test.customTextView
  android:id="@+id/hj1"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:layout_below="@+id/hj2"
  android:text="Custom normal" />

2. Bold font
<com.example.test.customTextView
  android:id="@+id/hj"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:layout_below="@+id/hj1"
  android:text="custom bold"
  android:textStyle="bold" />
  
  3. Bold_Italic font
<com.example.test.customTextView
  android:id="@+id/hj"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:layout_below="@+id/hj1"
  android:text="custom bold"
  android:textStyle="bold|italic" />
  
  4. italic font
<com.example.test.customTextView
  android:id="@+id/hj"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:layout_below="@+id/hj1"
  android:text="custom bold"
  android:textStyle="italic" />