我来帮你搞定这个联动填充的需求，思路其实很清晰：监听Student ID输入框的变化，输入完成后去SQLite数据库匹配对应数据，查到结果就自动填到姓名字段里。下面是具体的实现方案和代码修改建议：

1. 给Student ID输入框添加焦点监听 #

为了避免频繁查询数据库，建议在用户输入完Student ID并离开输入框（失去焦点）时触发查询逻辑，这样更合理：

studentid.setOnFocusChangeListener(new View.OnFocusChangeListener() {
    @Override
    public void onFocusChange(View v, boolean hasFocus) {
        // 输入框失去焦点时执行查询
        if (!hasFocus) {
            String id = studentid.getText().toString().trim();
            if (!id.isEmpty()) {
                getStudentInfoById(id);
            } else {
                // ID为空时清空姓名字段
                fname.setText("");
                lname.setText("");
            }
        }
    }
});

2. 实现数据库查询方法 #

写一个专门的方法，根据Student ID从数据库中获取对应的姓名信息：

private void getStudentInfoById(String studentId) {
    Cursor cursor = null;
    try {
        // 使用占位符查询，避免SQL注入
        cursor = db.rawQuery("SELECT fname, lname FROM CUSTOMER_TABLE WHERE studentid = ?", new String[]{studentId});
        if (cursor.moveToFirst()) {
            // 提取查询结果并填充到对应输入框
            String firstName = cursor.getString(cursor.getColumnIndexOrThrow("fname"));
            String lastName = cursor.getString(cursor.getColumnIndexOrThrow("lname"));
            fname.setText(firstName);
            lname.setText(lastName);
        } else {
            // 未找到对应记录时清空字段并提示
            fname.setText("");
            lname.setText("");
            Toast.makeText(this, "No student found with this ID", Toast.LENGTH_SHORT).show();
        }
    } catch (Exception e) {
        e.printStackTrace();
        Toast.makeText(this, "Error querying database", Toast.LENGTH_SHORT).show();
    } finally {
        // 关闭Cursor，防止内存泄漏
        if (cursor != null) {
            cursor.close();
        }
    }
}

3. 完整的MainActivity修改后代码 #

把上面的逻辑整合到你的代码中，同时补全你未完成的Add按钮点击事件：

public class MainActivity extends Activity {
    EditText fname, lname, classid, classname, pointgrade, lettergrade, studentid;
    Button add, viewall, delete, modifystudent, modifyclass, modifygrade;
    SQLiteDatabase db;

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

        // 初始化所有控件
        studentid = findViewById(R.id.studentID);
        fname = findViewById(R.id.firstName);
        lname = findViewById(R.id.lastName);
        classid = findViewById(R.id.classID);
        classname = findViewById(R.id.className);
        pointgrade = findViewById(R.id.gradePoint);
        lettergrade = findViewById(R.id.letterGrade);

        add = findViewById(R.id.addbtn);
        viewall = findViewById(R.id.viewall);
        delete = findViewById(R.id.deletebtn);
        modifystudent = findViewById(R.id.modifystudent);
        modifyclass = findViewById(R.id.modifyclass);
        modifygrade = findViewById(R.id.modifygrade);

        // 初始化数据库
        db = openOrCreateDatabase("STUDENTGRADES", Context.MODE_PRIVATE, null);
        db.execSQL("CREATE TABLE IF NOT EXISTS CUSTOMER_TABLE(studentid VARCHAR, fname VARCHAR, lname VARCHAR, classid VARCHAR, classname VARCHAR, pointgrade INTEGER, lettergrade VARCHAR);");

        // 添加Student ID的焦点监听，触发自动填充
        studentid.setOnFocusChangeListener(new View.OnFocusChangeListener() {
            @Override
            public void onFocusChange(View v, boolean hasFocus) {
                if (!hasFocus) {
                    String id = studentid.getText().toString().trim();
                    if (!id.isEmpty()) {
                        getStudentInfoById(id);
                    } else {
                        fname.setText("");
                        lname.setText("");
                    }
                }
            }
        });

        // 补全Add按钮的点击事件
        add.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String id = studentid.getText().toString().trim();
                String first = fname.getText().toString().trim();
                String last = lname.getText().toString().trim();
                String cid = classid.getText().toString().trim();
                String cname = classname.getText().toString().trim();
                String point = pointgrade.getText().toString().trim();
                String letter = lettergrade.getText().toString().trim();

                // 简单非空校验
                if (id.isEmpty() || first.isEmpty() || last.isEmpty()) {
                    Toast.makeText(MainActivity.this, "Please fill required fields", Toast.LENGTH_SHORT).show();
                    return;
                }

                // 用ContentValues插入数据，更安全规范
                ContentValues values = new ContentValues();
                values.put("studentid", id);
                values.put("fname", first);
                values.put("lname", last);
                values.put("classid", cid);
                values.put("classname", cname);
                values.put("pointgrade", point.isEmpty() ? 0 : Integer.parseInt(point));
                values.put("lettergrade", letter);
                db.insert("CUSTOMER_TABLE", null, values);

                Toast.makeText(MainActivity.this, "Record added successfully", Toast.LENGTH_SHORT).show();
                clearAllFields();
            }
        });

        // 其他按钮的点击事件可以继续补充...
    }

    // 查询学生信息的方法
    private void getStudentInfoById(String studentId) {
        Cursor cursor = null;
        try {
            cursor = db.rawQuery("SELECT fname, lname FROM CUSTOMER_TABLE WHERE studentid = ?", new String[]{studentId});
            if (cursor.moveToFirst()) {
                String firstName = cursor.getString(cursor.getColumnIndexOrThrow("fname"));
                String lastName = cursor.getString(cursor.getColumnIndexOrThrow("lname"));
                fname.setText(firstName);
                lname.setText(lastName);
            } else {
                fname.setText("");
                lname.setText("");
                Toast.makeText(this, "No matching student found", Toast.LENGTH_SHORT).show();
            }
        } catch (Exception e) {
            e.printStackTrace();
            Toast.makeText(this, "Database error occurred", Toast.LENGTH_SHORT).show();
        } finally {
            if (cursor != null) {
                cursor.close();
            }
        }
    }

    // 清空所有输入框的辅助方法
    private void clearAllFields() {
        studentid.setText("");
        fname.setText("");
        lname.setText("");
        classid.setText("");
        classname.setText("");
        pointgrade.setText("");
        lettergrade.setText("");
    }

    // 销毁Activity时关闭数据库连接
    @Override
    protected void onDestroy() {
        super.onDestroy();
        if (db != null && db.isOpen()) {
            db.close();
        }
    }
}

4. 格式化后的XML布局代码 #

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/LinearLayout1"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#d5ebfd"
    android:orientation="vertical">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="40dp"
        android:fontFamily="serif"
        android:gravity="center"
        android:text="Student Grade Management System"
        android:textColor="#ff0000"
        android:textSize="20sp"
        android:textStyle="bold"/>

    <EditText
        android:id="@+id/studentID"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="Enter Student ID (Used for Updating/Deleting): "
        android:inputType="number"
        android:paddingTop="20dp" />

    <requestFocus />

    <EditText
        android:id="@+id/firstName"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="Enter First Name: " />

    <EditText
        android:id="@+id/lastName"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="Enter Last Name: " />

    <EditText
        android:id="@+id/classID"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="Enter Class ID: "
        android:inputType="number" />

    <EditText
        android:id="@+id/className"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="Enter Class Name: " />

    <EditText
        android:id="@+id/gradePoint"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="Enter Grade Point (0-100): "
        android:inputType="number" />

    <EditText
        android:id="@+id/letterGrade"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="Enter Letter Grade: " />

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="50dp">

        <Button
            android:id="@+id/addbtn"
            android:layout_width="200dp"
            android:layout_height="50dp"
            android:text="Add" />

        <Button
            android:id="@+id/deletebtn"
            android:layout_width="200dp"
            android:layout_height="50dp"
            android:text="Delete" />
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="50dp">

        <Button
            android:id="@+id/viewall"
            android:layout_width="200dp"
            android:layout_height="50dp"
            android:text="View" />

        <Button
            android:id="@+id/modifystudent"
            android:layout_width="200dp"
            android:layout_height="50dp"
            android:text="Update Student Info" />
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="50dp">

        <Button
            android:id="@+id/modifyclass"
            android:layout_width="200dp"
            android:layout_height="50dp"
            android:text="Update Class Info" />

        <Button
            android:id="@+id/modifygrade"
            android:layout_width="200dp"
            android:layout_height="50dp"
            android:text="Update Grade Info" />
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="0.74">
    </LinearLayout>
</LinearLayout>

额外小建议 #

• 如果想要实时监听输入（比如每输入一个字符就查询），可以用TextWatcher的afterTextChanged方法，但记得加个延迟（比如用Handler.postDelayed），避免频繁查询影响性能。
• 数据库操作建议放在子线程中执行，避免阻塞主线程导致UI卡顿，后续可以考虑用AsyncTask或者Coroutine优化。

内容的提问来源于stack exchange，提问作者Tanner Tattini