Add font preview to font preference picker dialog

app/src/main/java/be/robinj/distrohopper/preferences/FontListPreferenceDialogFragment.kt

@@ -0,0 +1,79 @@
+package be.robinj.distrohopper.preferences
+
+import android.content.DialogInterface
+import android.graphics.Typeface
+import android.os.Bundle
+import android.view.View
+import android.view.ViewGroup
+import android.widget.ArrayAdapter
+import android.widget.TextView
+import androidx.appcompat.app.AlertDialog
+import androidx.preference.ListPreference
+
+/**
+ * The Appearance font picker. Behaves like the framework's list-preference dialog
+ * (single-choice, tap-to-select-and-dismiss) but renders each option in the font
+ * it names — the "Ubuntu" row is drawn in Ubuntu, "Oxygen" in Oxygen, and so on —
+ * so the user previews each font while choosing it. "System default" keeps the
+ * device font.
+ *
+ * We can't just let the base class build the list because it wires up a private
+ * clicked-index field we can't reach, so this replicates its select-and-persist
+ * flow with a custom adapter (see [onPrepareDialogBuilder] / [onDialogClosed]).
+ * Extends the frosted variant so the legibility fallback is preserved.
+ */
+class FontListPreferenceDialogFragment :
+	PreferencesActivity.FrostedListPreferenceDialogFragment() {
+
+	private var clickedIndex = -1
+
+	override fun onPrepareDialogBuilder(builder: AlertDialog.Builder) {
+		val listPreference = this.preference as ListPreference
+		val entries = listPreference.entries
+		val entryValues = listPreference.entryValues
+		this.clickedIndex = listPreference.findIndexOfValue(listPreference.value)
+
+		val adapter = object : ArrayAdapter<CharSequence>(
+			this.requireContext(),
+			android.R.layout.select_dialog_singlechoice,
+			android.R.id.text1,
+			entries,
+		) {
+			override fun getView(position: Int, convertView: View?, parent: ViewGroup): View {
+				val view = super.getView(position, convertView, parent)
+				val textView = view.findViewById<TextView>(android.R.id.text1)
+				textView.typeface =
+					FontPreference.typefaceFor(this.context, entryValues[position]?.toString())
+						?: Typeface.DEFAULT
+				return view
+			}
+		}
+
+		// Mirror ListPreferenceDialogFragmentCompat: tapping a row selects it and
+		// immediately closes with a positive result (no separate OK button). //
+		builder.setSingleChoiceItems(adapter, this.clickedIndex) { dialog, which ->
+			this.clickedIndex = which
+			this.onClick(dialog, DialogInterface.BUTTON_POSITIVE)
+			dialog.dismiss()
+		}
+		builder.setPositiveButton(null, null)
+	}
+
+	override fun onDialogClosed(positiveResult: Boolean) {
+		if (positiveResult && this.clickedIndex >= 0) {
+			val listPreference = this.preference as ListPreference
+			val value = listPreference.entryValues[this.clickedIndex].toString()
+			if (listPreference.callChangeListener(value)) {
+				listPreference.value = value
+			}
+		}
+	}
+
+	companion object {
+		fun newInstance(key: String): FontListPreferenceDialogFragment {
+			val fragment = FontListPreferenceDialogFragment()
+			fragment.arguments = Bundle(1).apply { this.putString("key", key) }
+			return fragment
+		}
+	}
+}

app/src/main/java/be/robinj/distrohopper/preferences/FontPreference.kt

@@ -42,6 +42,17 @@ object FontPreference {
 		return ResourcesCompat.getFont(context, fontRes)
 	}
 
+	/**
+	 * The [Typeface] for a given font preference [value], or null when [value] is
+	 * System / unknown (i.e. the system font should be used). Unlike [typeface]
+	 * this ignores the stored preference and resolves whatever value is passed,
+	 * so the picker can render each option in its own font.
+	 */
+	fun typefaceFor(context: Context, value: String?): Typeface? {
+		val fontRes = this.fontResFor(value) ?: return null
+		return ResourcesCompat.getFont(context, fontRes)
+	}
+
 	private fun current(context: Context): String =
 		Preferences.getSharedPreferences(context)
 			.getString(Preference.FONT.getName(), SYSTEM) ?: SYSTEM

app/src/main/java/be/robinj/distrohopper/preferences/PreferencesActivity.java

@@ -322,8 +322,13 @@ public void onDisplayPreferenceDialog (final Preference preference)
 
 			if (preference instanceof ListPreference)
 			{
+				// The font picker previews each option in its own font; every other
+				// list preference uses the plain frosted dialog. //
 				final DialogFragment fragment =
-					FrostedListPreferenceDialogFragment.newInstance (preference.getKey ());
+					be.robinj.distrohopper.preferences.Preference.FONT.getName ()
+						.equals (preference.getKey ())
+						? FontListPreferenceDialogFragment.newInstance (preference.getKey ())
+						: FrostedListPreferenceDialogFragment.newInstance (preference.getKey ());
 				fragment.setTargetFragment (this, 0);
 				fragment.show (this.getParentFragmentManager (), DIALOG_FRAGMENT_TAG);
 			}