写一个Android学生信息管理系统实例

好的，以下是一个简单的Android学生信息管理系统实例的代码：

首先，我们需要创建一个MainActivity来作为应用程序的主界面。在该Activity中，我们可以添加按钮来实现添加、删除、修改和查询学生信息的功能。

public class MainActivity extends AppCompatActivity {
    private Button addBtn, deleteBtn, updateBtn, queryBtn;
    private EditText nameEt, ageEt, phoneEt, emailEt;
    private ListView studentListView;
    private SQLiteDatabase db;
    private StudentAdapter studentAdapter;

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

        addBtn = findViewById(R.id.add_btn);
        deleteBtn = findViewById(R.id.delete_btn);
        updateBtn = findViewById(R.id.update_btn);
        queryBtn = findViewById(R.id.query_btn);
        nameEt = findViewById(R.id.name_et);
        ageEt = findViewById(R.id.age_et);
        phoneEt = findViewById(R.id.phone_et);
        emailEt = findViewById(R.id.email_et);
        studentListView = findViewById(R.id.student_list_view);

        // 创建或打开数据库
        db = openOrCreateDatabase("student.db", MODE_PRIVATE, null);
        db.execSQL("CREATE TABLE IF NOT EXISTS student(_id INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT, age INTEGER, phone TEXT, email TEXT)");

        // 设置ListView的适配器
        studentAdapter = new StudentAdapter(this);
        studentListView.setAdapter(studentAdapter);

        // 添加按钮点击事件
        addBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String name = nameEt.getText().toString();
                int age = Integer.parseInt(ageEt.getText().toString());
                String phone = phoneEt.getText().toString();
                String email = emailEt.getText().toString();
                ContentValues cv = new ContentValues();
                cv.put("name", name);
                cv.put("age", age);
                cv.put("phone", phone);
                cv.put("email", email);
                db.insert("student", null, cv);
                studentAdapter.notifyDataSetChanged();
            }
        });

        // 删除按钮点击事件
        deleteBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String name = nameEt.getText().toString();
                db.delete("student", "name=?", new String[]{name});
                studentAdapter.notifyDataSetChanged();
            }
        });

        // 修改按钮点击事件
        updateBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String name = nameEt.getText().toString();
                int age = Integer.parseInt(ageEt.getText().toString());
                String phone = phoneEt.getText().toString();
                String email = emailEt.getText().toString();
                ContentValues cv = new ContentValues();
                cv.put("age", age);
                cv.put("phone", phone);
                cv.put("email", email);
                db.update("student", cv, "name=?", new String[]{name});
                studentAdapter.notifyDataSetChanged();
            }
        });

        // 查询按钮点击事件
        queryBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String name = nameEt.getText().toString();
                Cursor cursor = db.query("student", null, "name=?", new String[]{name}, null, null, "_id DESC");
                if (cursor.moveToFirst()) {
                    int age = cursor.getInt(cursor.getColumnIndex("age"));
                    String phone = cursor.getString(cursor.getColumnIndex("phone"));
                    String email = cursor.getString(cursor.getColumnIndex("email"));
                    ageEt.setText(age + "");
                    phoneEt.setText(phone);
                    emailEt.setText(email);
                } else {
                    ageEt.setText("");
                    phoneEt.setText("");
                    emailEt.setText("");
                    Toast.makeText(MainActivity.this, "没有找到该学生信息", Toast.LENGTH_SHORT).show();
                }
                cursor.close();
            }
        });
    }

    // 自定义ListView的适配器
    private class StudentAdapter extends BaseAdapter {
        private Context context;
        private Cursor cursor;

        public StudentAdapter(Context context) {
            this.context = context;
            cursor = db.query("student", null, null, null, null, null, "_id DESC");
        }

        @Override
        public int getCount() {
            return cursor.getCount();
        }

        @Override
        public Object getItem(int position) {
            return null;
        }

        @Override
        public long getItemId(int position) {
            return 0;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            if (convertView == null) {
                convertView = LayoutInflater.from(context).inflate(R.layout.student_list_item, null);
            }
            TextView nameTv = convertView.findViewById(R.id.name_tv);
            TextView ageTv = convertView.findViewById(R.id.age_tv);
            TextView phoneTv = convertView.findViewById(R.id.phone_tv);
            TextView emailTv = convertView.findViewById(R.id.email_tv);
            cursor.moveToPosition(position);
            String name = cursor.getString(cursor.getColumnIndex("name"));
            int age = cursor.getInt(cursor.getColumnIndex("age"));
            String phone = cursor.getString(cursor.getColumnIndex("phone"));
            String email = cursor.getString(cursor.getColumnIndex("email"));
            nameTv.setText(name);
            ageTv.setText(age + "");
            phoneTv.setText(phone);
            emailTv.setText(email);
            return convertView;
        }
    }
}

在布局文件中，我们需要添加一个ListView和一些EditText和Button来实现添加、删除、修改和查询学生信息的功能。

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

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        android:padding="16dp">

        <EditText
            android:id="@+id/name_et"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:hint="姓名" />

        <EditText
            android:id="@+id/age_et"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:hint="年龄" />

        <EditText
            android:id="@+id/phone_et"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:hint="电话" />

        <EditText
            android:id="@+id/email_et"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:hint="邮箱" />
    </LinearLayout>

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/name_et"
        android:layout_marginTop="16dp"
        android:layout_centerHorizontal="true"
        android:orientation="horizontal">

        <Button
            android:id="@+id/add_btn"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="添加" />

        <Button
            android:id="@+id/delete_btn"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="删除" />

        <Button
            android:id="@+id/update_btn"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="修改" />

        <Button
            android:id="@+id/query_btn"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="查询" />
    </LinearLayout>

    <ListView
        android:id="@+id/student_list_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_below="@id/add_btn" />

</RelativeLayout>

最后，我们需要创建一个用于显示每个学生信息的ListView的适配器StudentAdapter。在该适配器中，我们需要从数据库中读取学生信息，然后将它们显示在ListView中。

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    android:padding="16dp">

    <TextView
        android:id="@+id/name_tv"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="姓名"
        android:textSize="16sp" />

    <TextView
        android:id="@+id/age_tv"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="年龄"
        android:textSize="16sp" />

    <TextView
        android:id="@+id/phone_tv"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="电话"
        android:textSize="16sp" />

    <TextView
        android:id="@+id/email_tv"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="邮箱"
        android:textSize="16sp" />

</LinearLayout>

这样，我们就完成了一个简单的Android学生信息管理系统实例。