add font setting

app/src/main/java/com/darkempire78/opencalculator/FontManager.kt

@@ -0,0 +1,51 @@
+package com.darkempire78.opencalculator
+
+import android.app.Activity
+import android.app.Application
+import android.content.Context
+import android.graphics.Typeface
+import android.os.Bundle
+import android.view.View
+import android.view.ViewGroup
+import android.view.ViewTreeObserver
+import android.widget.TextView
+
+class FontManager(context: Context) {
+    val context: Context = context.applicationContext
+    fun applyFont(application: Application) {
+        val fontName = MyPreferences(context).appFont
+        if (fontName != null && fontName != "Default") {
+            val typeface = Typeface.createFromAsset(context.assets, "font/$fontName.ttf")
+            // Apply the typeface to all activities
+            application.registerActivityLifecycleCallbacks(object : Application.ActivityLifecycleCallbacks {
+                override fun onActivityCreated(activity: Activity, savedInstanceState: Bundle?) {
+                    activity.findViewById<View>(android.R.id.content).viewTreeObserver
+                        .addOnGlobalLayoutListener(object : ViewTreeObserver.OnGlobalLayoutListener {
+                            override fun onGlobalLayout() {
+                                val rootView = activity.findViewById<ViewGroup>(android.R.id.content)
+                                applyFontToViewGroup(rootView, typeface)
+                                rootView.viewTreeObserver.removeOnGlobalLayoutListener(this)
+                            }
+                        })
+                }
+                override fun onActivityStarted(activity: Activity) {}
+                override fun onActivityResumed(activity: Activity) {}
+                override fun onActivityPaused(activity: Activity) {}
+                override fun onActivityStopped(activity: Activity) {}
+                override fun onActivitySaveInstanceState(activity: Activity, outState: Bundle) {}
+                override fun onActivityDestroyed(activity: Activity) {}
+            })
+        }
+    }
+
+    private fun applyFontToViewGroup(viewGroup: ViewGroup, typeface: Typeface) {
+        for (i in 0 until viewGroup.childCount) {
+            val child = viewGroup.getChildAt(i)
+            if (child is ViewGroup) {
+                applyFontToViewGroup(child, typeface)
+            } else if (child is TextView) {
+                child.typeface = typeface
+            }
+        }
+    }
+}

app/src/main/java/com/darkempire78/opencalculator/MyPreferences.kt

@@ -1,6 +1,9 @@
 package com.darkempire78.opencalculator
 
 import android.content.Context
+import android.graphics.Typeface
+import android.view.ViewGroup
+import android.widget.TextView
 import androidx.appcompat.app.AppCompatDelegate.*
 import androidx.preference.PreferenceManager
 import com.google.gson.Gson
@@ -25,6 +28,7 @@ class MyPreferences(context: Context) {
         private const val KEY_SPLIT_PARENTHESIS_BUTTON = "darkempire78.opencalculator.SPLIT_PARENTHESIS_BUTTON"
         private const val KEY_DELETE_HISTORY_ON_SWIPE = "darkempire78.opencalculator.DELETE_HISTORY_ELEMENT_ON_SWIPE"
         private const val KEY_AUTO_SAVE_CALCULATION_WITHOUT_EQUAL_BUTTON = "darkempire78.opencalculator.AUTO_SAVE_CALCULATION_WITHOUT_EQUAL_BUTTON"
+        private const val KEY_APP_FONT = "darkempire78.opencalculator.APP_FONT"
     }
 
     private val preferences = PreferenceManager.getDefaultSharedPreferences(context)
@@ -61,6 +65,8 @@ class MyPreferences(context: Context) {
 
     var autoSaveCalculationWithoutEqualButton = preferences.getBoolean(KEY_AUTO_SAVE_CALCULATION_WITHOUT_EQUAL_BUTTON, true)
         set(value) = preferences.edit().putBoolean(KEY_AUTO_SAVE_CALCULATION_WITHOUT_EQUAL_BUTTON, value).apply()
+    var appFont = preferences.getString(KEY_APP_FONT, "default")
+        set(value) = preferences.edit().putString(KEY_APP_FONT, value).apply()
 
 
     fun getHistory(): MutableList<History> {

app/src/main/java/com/darkempire78/opencalculator/OpenCalcApp.kt

@@ -1,12 +1,20 @@
 package com.darkempire78.opencalculator
 
+import android.app.Activity
 import android.app.Application
+import android.graphics.Typeface
+import android.os.Bundle
+import android.view.View
+import android.view.ViewGroup
+import android.view.ViewTreeObserver
+import android.widget.TextView
 import androidx.appcompat.app.AppCompatDelegate.*
 
 class OpenCalcApp : Application() {
 
     override fun onCreate() {
         super.onCreate()
+        FontManager(this).applyFont(this)
 
         // if the theme is overriding the system, the first creation doesn't work properly
         val forceDayNight = MyPreferences(this).forceDayNight

app/src/main/java/com/darkempire78/opencalculator/SettingsActivity.kt

@@ -2,13 +2,16 @@ package com.darkempire78.opencalculator
 
 import android.content.Intent
 import android.content.res.Resources.Theme
+import android.graphics.Typeface
 import android.net.Uri
 import android.os.Build
 import android.os.Bundle
 import android.provider.Settings
 import android.view.View
+import android.view.ViewGroup
 import android.widget.FrameLayout
 import android.widget.ImageView
+import android.widget.TextView
 import androidx.annotation.RequiresApi
 import androidx.appcompat.app.AppCompatActivity
 import androidx.core.content.ContextCompat
@@ -29,9 +32,9 @@ class SettingsActivity : AppCompatActivity() {
         setContentView(R.layout.settings_activity)
         if (savedInstanceState == null) {
             supportFragmentManager
-                    .beginTransaction()
-                    .replace(R.id.settings, SettingsFragment())
-                    .commit()
+                .beginTransaction()
+                .replace(R.id.settings, SettingsFragment())
+                .commit()
         }
         supportActionBar?.setDisplayHomeAsUpEnabled(true)
 
@@ -46,7 +49,6 @@ class SettingsActivity : AppCompatActivity() {
         findViewById<ImageView>(R.id.settings_back_button).setOnClickListener {
             finish()
         }
-
     }
 
     class SettingsFragment : PreferenceFragmentCompat() {
@@ -55,7 +57,7 @@ class SettingsActivity : AppCompatActivity() {
 
             val appLanguagePreference = findPreference<Preference>("darkempire78.opencalculator.APP_LANGUAGE")
 
-            // remove the app language button if you are using an Android version lower than v33 (Android 13)
+            // Remove the app language button if you are using an Android version lower than v33 (Android 13)
             if (Build.VERSION.SDK_INT < Build.VERSION_CODES.TIRAMISU) {
                 appLanguagePreference?.isVisible = false
             } else {
@@ -79,6 +81,30 @@ class SettingsActivity : AppCompatActivity() {
                 Themes.openDialogThemeSelector(this.requireContext())
                 true
             }
+
+            // Font preference
+            val appFontPreference = findPreference<Preference>("darkempire78.opencalculator.APP_FONT")
+            appFontPreference?.setOnPreferenceChangeListener { _, newValue ->
+                applyFont(newValue as String)
+                true
+            }
+        }
+
+        private fun applyFont(fontName: String) {
+            val typeface = Typeface.createFromAsset(requireContext().assets, "font/$fontName.ttf")
+            val rootView = requireActivity().findViewById<ViewGroup>(android.R.id.content)
+            applyFontToViewGroup(rootView, typeface)
+        }
+
+        private fun applyFontToViewGroup(viewGroup: ViewGroup, typeface: Typeface) {
+            for (i in 0 until viewGroup.childCount) {
+                val child = viewGroup.getChildAt(i)
+                if (child is ViewGroup) {
+                    applyFontToViewGroup(child, typeface)
+                } else if (child is TextView) {
+                    child.typeface = typeface
+                }
+            }
         }
 
         @RequiresApi(Build.VERSION_CODES.TIRAMISU)

app/src/main/res/drawable/font.xml

@@ -0,0 +1,9 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+android:width="30dp"
+android:height="30dp"
+android:viewportWidth="960"
+android:viewportHeight="960">
+<path
+    android:fillColor="@color/text_color"
+    android:pathData="M200,760L200,680L760,680L760,760L200,760ZM276,600L440,160L520,160L684,600L608,600L570,488L392,488L352,600L276,600ZM414,424L546,424L482,242L478,242L414,424Z"/>
+</vector>

app/src/main/res/values/arrays.xml

@@ -86,4 +86,16 @@
         <item>1000</item> <!-- Infinity -->
     </string-array>
 
+
+    <!-- App Font Setting-->
+    <string-array name="app_font_entries">
+        <item>Default</item>
+        <item>OpenSans</item>
+    </string-array>
+
+    <string-array name="app_font_values">
+        <item>default</item>
+        <item>open_sans_medium</item>
+    </string-array>
+
 </resources>

app/src/main/res/values/strings.xml

@@ -138,4 +138,5 @@
     <string name="require_real_number">Real number required</string>
     <string name="settings_auto_save_calculation_without_equal_button">Automatically save calculations</string>
     <string name="settings_auto_save_calculation_without_equal_button_desc">Automatically save calculations in history without needing to click the equal button</string>
+    <string name="settings_app_font">Font</string>
 </resources>

app/src/main/res/xml/root_preferences.xml

@@ -25,6 +25,16 @@
             app:summary="APP THEME"
             app:icon="@drawable/theme" />
 
+        <ListPreference
+            app:key="darkempire78.opencalculator.APP_FONT"
+            app:title="@string/settings_app_font"
+            app:entries="@array/app_font_entries"
+            app:entryValues="@array/app_font_values"
+            app:defaultValue="Default"
+            app:useSimpleSummaryProvider="true"
+            app:singleLineTitle="false"
+            app:icon="@drawable/font" />
+
         <SwitchPreferenceCompat
             app:key="darkempire78.opencalculator.KEY_VIBRATION_STATUS"
             app:title="@string/settings_general_vibration"