app/src/main/java/com/example/childguard/HomeFragment.java

@@ -1,12 +1,15 @@
 package com.example.childguard;
 
+import android.content.SharedPreferences;
 import android.os.Bundle;
 
 import androidx.fragment.app.Fragment;
 
+import android.util.Log;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
+import android.widget.TextView;
 
 /**
  * A simple {@link Fragment} subclass.
@@ -61,4 +64,23 @@ public class HomeFragment extends Fragment {
         // Inflate the layout for this fragment
         return inflater.inflate(R.layout.fragment_home, container, false);
     }
+
+    @Override
+    public void onResume() {
+        super.onResume();
+        Log.d("HomeFragment", "onResume: called");
+        TextView situationTextView = getView().findViewById(R.id.situation);
+        updateInCarStatus(situationTextView);
+    }
+
+    public void updateInCarStatus(TextView situationTextView) {
+        SharedPreferences sharedPreferences = getActivity().getSharedPreferences("default", 0);
+
+        Log.d("HomeFragment", "updateInCarStatus: " + sharedPreferences.getBoolean("inCar", false));
+        if (sharedPreferences.getBoolean("inCar", false)) {
+            situationTextView.setText("\n降車状態");
+        } else {
+            situationTextView.setText("\n乗車状態");
+        }
+    }
 }

app/src/main/java/com/example/childguard/QRFragment.java

@@ -5,6 +5,7 @@ import android.os.Bundle;
 
 import androidx.fragment.app.Fragment;
 
+import android.util.Log;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
@@ -67,6 +68,19 @@ public class QRFragment extends Fragment {
 
         Button cameraButton = view.findViewById(R.id.camera);
 
+        // Init shared preferences
+        SharedPreferences sharedPreferences = getActivity().getSharedPreferences("default", 0);
+        SharedPreferences.Editor editor = sharedPreferences.edit();
+
+        cameraButton.setOnClickListener(v -> {
+            Log.d("QRFragment", "onClick: called");
+            if (!sharedPreferences.getBoolean("inCar", false)) {
+                editor.putBoolean("inCar", true);
+            } else {
+                editor.putBoolean("inCar", false);
+            }
+            editor.apply();
+        });
 
         return view;
     }