classIdを受け取るロジックが画面遷移から戻ってきたときにも実行されるように変更

.idea/gradle.xml

@@ -4,6 +4,7 @@
   <component name="GradleSettings">
     <option name="linkedExternalProjectsSettings">
       <GradleProjectSettings>
+        <option name="testRunner" value="GRADLE" />
         <option name="externalProjectPath" value="$PROJECT_DIR$" />
         <option name="gradleJvm" value="#GRADLE_LOCAL_JAVA_HOME" />
         <option name="modules">

app/src/main/java/com/example/oplogy/AppDatabase.java

@@ -3,7 +3,7 @@ package com.example.oplogy;
 import androidx.room.Database;
 import androidx.room.RoomDatabase;
 
-@Database(entities = {SetUpTable.class}, version = 2)
+@Database(entities = {SetUpTable.class}, version = 2, exportSchema = false)
 public abstract class AppDatabase extends RoomDatabase {
     // データベースにアクセスするためのメソッドを提供する
     public abstract SetUpTableDao setUpTableDao();

app/src/main/java/com/example/oplogy/CreateUUID.java

@@ -5,12 +5,12 @@ import java.util.List;
 
 public class CreateUUID {
 
-    public static String generateUUID(List<String> classIdList ){
+    public static int generateUUID(List<String> classIdList ){
         while (true){
-            String uuid = String.valueOf((int)(Math.random()*100000));
+            String uuid = String.valueOf((int)(Math.random() * 1000000));
             boolean isDuplicate = false;
             for(String classId : classIdList){
-                if(Integer.parseInt(classId) == Integer.parseInt(uuid)){
+                if(classId.equals(uuid)){
                     //重複があればフラグを立て、ループを抜ける
                     isDuplicate = true;
                     break;
@@ -19,7 +19,9 @@ public class CreateUUID {
             //重複がなければ生成したUUIDを返す
             if (!isDuplicate) {
                 //firestoreに挿入処理
-                return uuid;
+                //テスト用
+                uuid="100";
+                return Integer.parseInt(uuid);
             }
         }
     }

app/src/main/java/com/example/oplogy/MainActivity.java

@@ -156,7 +156,7 @@ public class MainActivity extends AppCompatActivity implements View.OnClickListe
         builder.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
             @Override
             public void onClick(DialogInterface dialog, int which) {
-                String classId = CreateUUID.generateUUID(classIdList);
+                classId = CreateUUID.generateUUID(classIdList);
                 Toast.makeText(MainActivity.this, "クラスID: " + classId, Toast.LENGTH_SHORT).show();
                 Log .d("classIdList", classIdList.toString());
 
@@ -292,4 +292,12 @@ public class MainActivity extends AppCompatActivity implements View.OnClickListe
         }
     }
 
+    @Override
+    protected void onResume(){
+        super.onResume();
+        if (classId != 100000) {
+            firestoreReception.getDocumentsByClassId(classId);
+        }
+    }
+
 }