Is there any option to change fonts of Android app

Question

I want to know if I have a text like "hello world". How can I set the preference of this text view that user can change the font size to medium, large and small like 20sp, 25sp, 30sp.

Answer 1

If you have an activity, which layout have a

 <TextView
    android:layout_width="match_parent"
    android:layout_height="wrap_content" 
    android:text="Hello World"
    android:textSize="20sp"
    />

so, you need an user input like buttons and in the activity you can changue the size of the textview element detecting an event relate to the user input, in this example the "onclick" method.

here is the code to archieve that.

layout:

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

<TextView
    android:id="@+id/txt_hello_world"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" 
    android:layout_centerInParent="true"
    android:text="HelloWorld"
    android:textColor="@android:color/black"
    android:textSize="20sp"
    />
<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_below="@id/txt_hello_world"
    android:orientation="horizontal"
    >

    <Button
        android:id="@+id/btn_20sp"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:layout_margin="8dp"
        android:text="20sp"
        />


    <Button
        android:id="@+id/btn_30sp"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:layout_margin="8dp"
        android:text="30sp"
        />

    <Button
        android:id="@+id/btn_40sp"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:layout_margin="8dp"
        android:text="40sp"
        />

</LinearLayout>

Activity

 class MainActivity : AppCompatActivity(), View.OnClickListener {
    lateinit var helloText : TextView
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        helloText  = findViewById(R.id.txt_hello_world)
        var btn20sp: Button = findViewById(R.id.btn_20sp)
        btn20sp.setOnClickListener(this)
        var btn30sp: Button = findViewById(R.id.btn_30sp)
        btn30sp.setOnClickListener(this)
        var btn40sp: Button = findViewById(R.id.btn_40sp)
        btn40sp.setOnClickListener(this)


    }

    override fun onClick(view: View) {
        when (view.id){
            R.id.btn_20sp -> helloText.setTextSize(TypedValue.COMPLEX_UNIT_SP,20f)
            R.id.btn_30sp -> helloText.setTextSize(TypedValue.COMPLEX_UNIT_SP,30f)
            R.id.btn_40sp -> helloText.setTextSize(TypedValue.COMPLEX_UNIT_SP,40f)
        }
      }
  }

The code is in kotlin but the logic is the samen in java