java - Android Studio，如何从Sqlite 数据库中检索数据并将其显示到textview 中？

Question

我在我的应用程序中创建了一个 SQLite 数据库，并将数据插入其中。现在我想从中检索数据，但我只想插入一个数据并检索它，然后将其显示到 TextView 中。

public class Db_sqlit extends SQLiteOpenHelper{

    String TABLE_NAME = "BallsTable";

    public final static String name = "db_data";

    public Db_sqlit(Context context) {
        super(context, name, null, 1);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL("create table "+TABLE_NAME+" (id INTEGER PRIMARY KEY AUTOINCREMENT, ball TEXT)");

    }

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

    public boolean insertData(String balls){
      SQLiteDatabase db = this.getWritableDatabase();
      ContentValues contentValues = new ContentValues();

      contentValues.put("ball",balls);

      long result = db.insert(TABLE_NAME,null,contentValues);
      if(result == -1){
          return false;
      }
      else
          return true;
    }

    public void list_balls(TextView textView) {

        Cursor res = this.getReadableDatabase().rawQuery("select ball from "+TABLE_NAME+"",null);
        textView.setText("");
        while (res.moveToNext()){
            textView.append(res.getString(1));
        }  
    }
}

Answer 1

这是我如何实现这一目标的示例。

在这个例子中，我将存储、检索、更新和删除一个学生的姓名和年龄。

---

首先创建一个类，我叫我的

DBManager.java

public class DBManager {
    private Context context;
    private SQLiteDatabase database;
    private SQLiteHelper dbHelper;

    public DBManager(Context c) {
        this.context = c;
    }

    public DBManager open() throws SQLException {
        this.dbHelper = new SQLiteHelper(this.context);
        this.database = this.dbHelper.getWritableDatabase();
        return this;
    }

    public void close() {
        this.dbHelper.close();
    }

    public void insert(String name, String desc) {
        ContentValues contentValue = new ContentValues();
        contentValue.put(SQLiteHelper.NAME, name);
        contentValue.put(SQLiteHelper.AGE, desc);
        this.database.insert(SQLiteHelper.TABLE_NAME_STUDENT, null, contentValue);
    }


    public Cursor fetch() {
        Cursor cursor = this.database.query(SQLiteHelper.TABLE_NAME_STUDENT, new String[]{SQLiteHelper._ID, SQLiteHelper.NAME, SQLiteHelper.AGE}, null, null, null, null, null);
        if (cursor != null) {
            cursor.moveToFirst();
        }
        return cursor;
    }

    public int update(long _id, String name, String desc) {
        ContentValues contentValues = new ContentValues();
        contentValues.put(SQLiteHelper.NAME, name);
        contentValues.put(SQLiteHelper.AGE, desc);
        return this.database.update(SQLiteHelper.TABLE_NAME_STUDENT, contentValues, "_id = " + _id, null);
    }

    public void delete(long _id) {
        this.database.delete(SQLiteHelper.TABLE_NAME_STUDENT, "_id=" + _id, null);
    }
}

然后创建一个SQLiteOpenHelper 我叫我的

SQLiteHelper.java

public class SQLiteHelper extends SQLiteOpenHelper {
    public static final String AGE = "age";
    private static final String CREATE_TABLE_STUDENT = " create table STUDENTS ( _id INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT NOT NULL , age TEXT );";
    private static final String DB_NAME = "STUDENTS.DB";
    private static final int DB_VERSION = 1;
    public static final String NAME = "name";
    public static final String TABLE_NAME_STUDENT = "STUDENTS";
    public static final String _ID = "_id";

    public SQLiteHelper(Context context) {
        super(context, DB_NAME, null, 1);
    }

    public void onCreate(SQLiteDatabase db) {
        db.execSQL(CREATE_TABLE_STUDENT);
    }

    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS STUDENTS");
        onCreate(db);
    }   
}

---

要添加:

在此示例中，我从 EditText 中获取文本，当单击按钮时，我检查 EditText 是否为空。如果它不为空并且学生不存在，我将学生的姓名和年龄插入数据库。我显示一个 Toast，让用户知道状态:

btnAdd.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {
        if (edtName.getText().toString().trim().length() == 0) {
            Toast.makeText(getApplicationContext(), "Please provide your students name", Toast.LENGTH_SHORT).show();
        } else{
            try {
                if (edtAge.getText().toString().trim().length() != 0) {
                    String name = edtName.getText().toString().trim();
                    String age = edtAge.getText().toString().trim();
                    String query = "Select * From STUDENTS where name = '"+name+"'";
                    if(dbManager.fetch().getCount()>0){
                        Toast.makeText(getApplicationContext(), "Already Exist!", Toast.LENGTH_SHORT).show();
                    }else{
                        dbManager.insert(name, age);
                        Toast.makeText(getApplicationContext(), "Added successfully!", Toast.LENGTH_SHORT).show();                           
                    }

                } else {
                    Toast.makeText(getApplicationContext(), "please provide student age!", Toast.LENGTH_SHORT).show();                           
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }  
});

---

更新:

在这里，我在 EditText 中获取文本，并在单击按钮时更新学生。您还可以将以下内容放在 try/catch 中以确保它已成功更新。

btnupdate.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {
        String name = nameText.getText().toString();
        String age = ageText.getText().toString();
        dbManager.update(_id, name, age);
        Toast.makeText(getApplicationContext(), "Updated successfully!", Toast.LENGTH_SHORT).show();
    }
});

---

删除:

dbManager.delete(_id);
Toast.makeText(getApplicationContext(), "Deleted successfully!", Toast.LENGTH_SHORT).show();

---

获取:

在这里，我获取了学生的姓名并将其显示在 TextView

中

DBManager dbManager = new DBManager(getActivity());
dbManager.open();

Cursor cursor = dbManager.fetch();
cursor.moveToFirst();
final TextView studentName = (TextView) getActivity().findViewById(R.id.nameOfStudent);
studentName.settext(cursor.getString(0));