数据未从SQLite加载到Listview中

Question

我正在使用android studio创建一个简单的crud系统，但是记录被成功添加到数据库中。但是当我试图查看listview控件视图中的记录时，无法查看数据，显示任何错误。我附上了以下代码。我已经为Listview textViewList提供了ID名称。数据库类我创建了DatabaseHelper。

list user.Java

public class ListUsers extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_list_users);

        DatabaseHandler db = new DatabaseHandler(this);
        String[] users = db.getAllUsers();
        if (users != null) {
            for (String us : users) {
                Log.d("String Array Value", us);
            }
            db.close();
        }
        // Use your own layout
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, R.layout.support_simple_spinner_dropdown_item, R.id.textViewList, users);
}

DatabaseHelper

public class DatabaseHelper extends SQLiteOpenHelper {
    // Database Version
    private static final int DATABASE_VERSION = 1;
    // Database Name
    private static final String DATABASE_NAME = "userDB";
    // Employee table name
    private static final String TABLE_USERS = "users";

    private static String USER_ID =  "user_id";
    private static String NAME = "name";
    private static String PHONE = "phone";
    private static String ADDRESS = "address";

    public DatabaseHandler(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }
    @Override
    public void onCreate(SQLiteDatabase db) {
        String CREATE_USER_TABLE = "CREATE TABLE " + TABLE_USERS + "("
                + USER_ID + " INTEGER PRIMARY KEY,"
                + NAME + " TEXT,"
                + PHONE + " TEXT,"
                + ADDRESS + " TEXT"
                + ")";
        db.execSQL(CREATE_USER_TABLE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_USERS);
        // Create tables again
        onCreate(db);
    }
    // Adding new user
    public int addUser(User user)
    {
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put(NAME, user.getName());
        values.put(ADDRESS, user.getAddress());
        values.put(PHONE, user.getPhone());
        // Inserting Row
        int id = (int) db.insert(TABLE_USERS, null, values);
        db.close(); // Closing database connection
        return id;
    }

    //updating a existing user
    public int editUser(User user, String position) {
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put(NAME, user.getName());
        values.put(PHONE, user.getPhone());
        values.put(ADDRESS, user.getAddress());
        // updating row
        return db.update(TABLE_USERS, values, USER_ID + " = ?",
                new String[] { String.valueOf(position) });
    }

    public User getUser(String id) {
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor cursor = db.query(TABLE_USERS, new String[] { USER_ID,
                        NAME, ADDRESS, PHONE }, USER_ID + "=?",
                new String[] {String.valueOf(id)}, null, null, null, null);
        if (cursor != null)
            cursor.moveToFirst();

        User user = new User(cursor.getString(1),
                cursor.getString(2), cursor.getString(3));
        db.close();
        // return user
        return user;

    }

    // LIst all users
    public String[] getAllUsers() {
        ArrayList<String> usersList = new ArrayList<String>();
        String selectQuery = "SELECT  * FROM " + TABLE_USERS;
        try {
            SQLiteDatabase db = this.getReadableDatabase();
            Cursor cursor = db.rawQuery(selectQuery, null);
            // looping through all rows and adding to list
            if (cursor.moveToFirst()) {
                do {
                    String user = cursor.getString(1) + ", " + cursor.getString(2) +  ", " + cursor.getString(3);
                    usersList.add(user);
                } while (cursor.moveToNext());
            }

            String[] users = new String[usersList.size()];
            db.close();
            return (usersList.toArray(users));
        }
        catch(Exception e) {
         //   Log.d("Error in getting users from DB", e.getMessage());
            return null;
        }
    }
}

列表显示

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".ListUsers">


    <ListView
        android:id="@+id/textViewList"
        android:layout_width="357dp"
        android:layout_height="495dp"
        tools:layout_editor_absoluteX="19dp"
        tools:layout_editor_absoluteY="8dp" />
</LinearLayout>

Answer 1

在活动类的onCreate()中，您初始化并填充适配器， 但你忘了为ListView设置适配器，所以添加到最后：

ListView listView = findViewById(R.id.textViewList);
listView.setAdapter(adapter);