在Androidstudio中设计一个简单学生选课系统并给出代码

为了设计一个简单的学生选课系统，我们需要考虑以下几个方面：

1. 数据存储：我们需要在系统中存储学生和课程的信息，可以使用SQLite数据库进行存储。

2. 用户界面：我们需要提供一个界面来展示课程信息和学生信息，以及提供选课和退课的功能。

3. 业务逻辑：我们需要编写代码实现选课和退课的逻辑，以及显示课程和学生的信息。

下面是一个简单的学生选课系统的示例代码：

1. 首先，在Android Studio中创建一个新的项目，并添加SQLite库的依赖。

2. 创建一个名为Course的Java类，表示课程信息：

public class Course {
    private int id;
    private String name;
    private int capacity;

    public Course(int id, String name, int capacity) {
        this.id = id;
        this.name = name;
        this.capacity = capacity;
    }

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public int getCapacity() {
        return capacity;
    }

    public void setCapacity(int capacity) {
        this.capacity = capacity;
    }
}

3. 创建一个名为Student的Java类，表示学生信息：

public class Student {
    private int id;
    private String name;
    private List<Course> courses;

    public Student(int id, String name) {
        this.id = id;
        this.name = name;
        this.courses = new ArrayList<>();
    }

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public List<Course> getCourses() {
        return courses;
    }

    public void addCourse(Course course) {
        courses.add(course);
    }

    public void removeCourse(Course course) {
        courses.remove(course);
    }
}

4. 创建一个名为DatabaseHelper的类，用于创建和管理SQLite数据库：

public class DatabaseHelper extends SQLiteOpenHelper {

    private static final String DATABASE_NAME = "courses.db";
    private static final int DATABASE_VERSION = 1;

    private static final String TABLE_COURSES = "courses";
    private static final String TABLE_STUDENTS = "students";
    private static final String TABLE_SELECTIONS = "selections";

    private static final String COLUMN_ID = "id";
    private static final String COLUMN_NAME = "name";
    private static final String COLUMN_CAPACITY = "capacity";
    private static final String COLUMN_STUDENT_ID = "student_id";
    private static final String COLUMN_COURSE_ID = "course_id";

    private static final String CREATE_TABLE_COURSES = "CREATE TABLE " + TABLE_COURSES +
            "(" + COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT," +
            COLUMN_NAME + " TEXT," +
            COLUMN_CAPACITY + " INTEGER)";

    private static final String CREATE_TABLE_STUDENTS = "CREATE TABLE " + TABLE_STUDENTS +
            "(" + COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT," +
            COLUMN_NAME + " TEXT)";

    private static final String CREATE_TABLE_SELECTIONS = "CREATE TABLE " + TABLE_SELECTIONS +
            "(" + COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT," +
            COLUMN_STUDENT_ID + " INTEGER," +
            COLUMN_COURSE_ID + " INTEGER," +
            "FOREIGN KEY(" + COLUMN_STUDENT_ID + ") REFERENCES " + TABLE_STUDENTS + "(" + COLUMN_ID + ")," +
            "FOREIGN KEY(" + COLUMN_COURSE_ID + ") REFERENCES " + TABLE_COURSES + "(" + COLUMN_ID + "))";

    public DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(CREATE_TABLE_COURSES);
        db.execSQL(CREATE_TABLE_STUDENTS);
        db.execSQL(CREATE_TABLE_SELECTIONS);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_SELECTIONS);
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_STUDENTS);
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_COURSES);
        onCreate(db);
    }
}

5. 创建一个名为MainActivity的类，用于实现界面和选课逻辑：

public class MainActivity extends AppCompatActivity {

    private DatabaseHelper dbHelper;

    private ListView courseListView;
    private ListView studentListView;

    private List<Course> courseList;
    private List<Student> studentList;

    private CourseAdapter courseAdapter;
    private StudentAdapter studentAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        dbHelper = new DatabaseHelper(this);

        courseListView = findViewById(R.id.course_list_view);
        studentListView = findViewById(R.id.student_list_view);

        courseList = new ArrayList<>();
        studentList = new ArrayList<>();

        courseAdapter = new CourseAdapter(this, courseList);
        studentAdapter = new StudentAdapter(this, studentList);

        courseListView.setAdapter(courseAdapter);
        studentListView.setAdapter(studentAdapter);

        updateData();

        courseListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                Course course = courseList.get(position);
                showCourseDialog(course);
            }
        });

        studentListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                Student student = studentList.get(position);
                showStudentDialog(student);
            }
        });
    }

    private void showCourseDialog(final Course course) {
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setTitle(course.getName());

        View view = LayoutInflater.from(this).inflate(R.layout.dialog_course, null);

        TextView capacityTextView = view.findViewById(R.id.capacity_text_view);
        final EditText capacityEditText = view.findViewById(R.id.capacity_edit_text);

        capacityTextView.setText("Capacity: " + course.getCapacity());
        capacityEditText.setText(String.valueOf(course.getCapacity()));

        builder.setView(view);

        builder.setPositiveButton("Save", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                int capacity = Integer.parseInt(capacityEditText.getText().toString());
                course.setCapacity(capacity);
                updateCourse(course);
            }
        });

        builder.setNegativeButton("Cancel", null);

        builder.show();
    }

    private void showStudentDialog(final Student student) {
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setTitle(student.getName());

        View view = LayoutInflater.from(this).inflate(R.layout.dialog_student, null);

        final ListView courseListView = view.findViewById(R.id.course_list_view);

        List<Course> availableCourses = getAvailableCourses(student);
        CourseAdapter adapter = new CourseAdapter(this, availableCourses);
        courseListView.setAdapter(adapter);

        builder.setView(view);

        builder.setPositiveButton("Add", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                int position = courseListView.getCheckedItemPosition();
                if (position != ListView.INVALID_POSITION) {
                    Course course = (Course) courseListView.getItemAtPosition(position);
                    addCourse(student, course);
                }
            }
        });

        builder.setNegativeButton("Remove", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                List<Course> selectedCourses = getSelectedCourses(student);
                Course[] courses = new Course[selectedCourses.size()];
                boolean[] checkedItems = new boolean[selectedCourses.size()];
                for (int i = 0; i < selectedCourses.size(); i++) {
                    courses[i] = selectedCourses.get(i);
                    checkedItems[i] = false;
                }
                AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this);
                builder.setTitle("Remove Courses");
                builder.setMultiChoiceItems(courses, checkedItems, new DialogInterface.OnMultiChoiceClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which, boolean isChecked) {
                        checkedItems[which] = isChecked;
                    }
                });
                builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        for (int i = 0; i < checkedItems.length; i++) {
                            if (checkedItems[i]) {
                                Course course = courses[i];
                                removeCourse(student, course);
                            }
                        }
                    }
                });
                builder.setNegativeButton("Cancel", null);
                builder.show();
            }
        });

        builder.show();
    }

    private void updateData() {
        courseList.clear();
        studentList.clear();

        SQLiteDatabase db = dbHelper.getReadableDatabase();

        Cursor cursor = db.rawQuery("SELECT * FROM " + DatabaseHelper.TABLE_COURSES, null);
        while (cursor.moveToNext()) {
            int id = cursor.getInt(cursor.getColumnIndex(DatabaseHelper.COLUMN_ID));
            String name = cursor.getString(cursor.getColumnIndex(DatabaseHelper.COLUMN_NAME));
            int capacity = cursor.getInt(cursor.getColumnIndex(DatabaseHelper.COLUMN_CAPACITY));
            Course course = new Course(id, name, capacity);
            courseList.add(course);
        }
        cursor.close();

        cursor = db.rawQuery("SELECT * FROM " + DatabaseHelper.TABLE_STUDENTS, null);
        while (cursor.moveToNext()) {
            int id = cursor.getInt(cursor.getColumnIndex(DatabaseHelper.COLUMN_ID));
            String name = cursor.getString(cursor.getColumnIndex(DatabaseHelper.COLUMN_NAME));
            Student student = new Student(id, name);
            studentList.add(student);
        }
        cursor.close();

        for (Student student : studentList) {
            cursor = db.rawQuery("SELECT * FROM " + DatabaseHelper.TABLE_SELECTIONS +
                    " WHERE " + DatabaseHelper.COLUMN_STUDENT_ID + " = ?", new String[]{String.valueOf(student.getId())});
            while (cursor.moveToNext()) {
                int courseId = cursor.getInt(cursor.getColumnIndex(DatabaseHelper.COLUMN_COURSE_ID));
                for (Course course : courseList) {
                    if (course.getId() == courseId) {
                        student.addCourse(course);
                        break;
                    }
                }
            }
            cursor.close();
        }

        courseAdapter.notifyDataSetChanged();
        studentAdapter.notifyDataSetChanged();
    }

    private void updateCourse(Course course) {
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put(DatabaseHelper.COLUMN_NAME, course.getName());
        values.put(DatabaseHelper.COLUMN_CAPACITY, course.getCapacity());
        db.update(DatabaseHelper.TABLE_COURSES, values, DatabaseHelper.COLUMN_ID + " = ?",
                new String[]{String.valueOf(course.getId())});
        updateData();
    }

    private List<Course> getAvailableCourses(Student student) {
        List<Course> availableCourses = new ArrayList<>();
        for (Course course : courseList) {
            if (!student.getCourses().contains(course) && course.getCapacity() > 0) {
                availableCourses.add(course);
            }
        }
        return availableCourses;
    }

    private List<Course> getSelectedCourses(Student student) {
        List<Course> selectedCourses = new ArrayList<>();
        for (Course course : courseList) {
            if (student.getCourses().contains(course)) {
                selectedCourses.add(course);
            }
        }
        return selectedCourses;
    }

    private void addCourse(Student student, Course course) {
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put(DatabaseHelper.COLUMN_STUDENT_ID, student.getId());
        values.put(DatabaseHelper.COLUMN_COURSE_ID, course.getId());
        db.insert(DatabaseHelper.TABLE_SELECTIONS, null, values);
        updateData();
    }

    private void removeCourse(Student student, Course course) {
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        db.delete(DatabaseHelper.TABLE_SELECTIONS,
                DatabaseHelper.COLUMN_STUDENT_ID + " = ? AND " + DatabaseHelper.COLUMN_COURSE_ID + " = ?",
                new String[]{String.valueOf(student.getId()), String.valueOf(course.getId())});
        updateData();
    }

    private static class CourseAdapter extends ArrayAdapter<Course> {

        public CourseAdapter(Context context, List<Course> courses) {
            super(context, 0, courses);
        }

        @NonNull
        @Override
        public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
            if (convertView == null) {
                convertView = LayoutInflater.from(getContext()).inflate(android.R.layout.simple_list_item_1, parent, false);
            }
            Course course = getItem(position);
            TextView textView = convertView.findViewById(android.R.id.text1);
            textView.setText(course.getName());
            return convertView;
        }
    }

    private static class StudentAdapter extends ArrayAdapter<Student> {

        public StudentAdapter(Context context, List<Student> students) {
            super(context, 0, students);
        }

        @NonNull
        @Override
        public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
            if (convertView == null) {
                convertView = LayoutInflater.from(getContext()).inflate(android.R.layout.simple_list_item_1, parent, false);
            }
            Student student = getItem(position);
            TextView textView = convertView.findViewById(android.R.id.text1);
            textView.setText(student.getName());
            return convertView;
        }
    }
}

6. 最后，在布局文件中添加ListView和对话框的布局：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ListView
        android:id="@+id/course_list_view"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1"/>

    <ListView
        android:id="@+id/student_list_view"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1"/>

</LinearLayout>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content">

    <TextView
        android:id="@+id/capacity_text_view"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>

    <EditText
        android:id="@+id/capacity_edit_text"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

</LinearLayout>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content">

    <ListView
        android:id="@+id/course_list_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:choiceMode="single"/>

</LinearLayout>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content">

    <ListView
        android:id="@+id/course_list_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:choiceMode="multiple"/>

</LinearLayout>

这样，一个简单的学生选课系统就完成了。