Android Sqlite 示例（带下拉列表）

在这个例子中，我们在按钮点击时添加一个标签，并在下拉列表上显示所有添加的标签。正如您在前面的例子中看到的一样， 需要扩展 SQLiteOpenHelper 类才能在sqlite上执行操作。

我们在 DatabaseHandler 类中覆盖了 SQLiteOpenHelper 类的 onCreate() 和 onUpgrade() 方法，该类提供了其他方法来插入和显示标签或数据。

Android Sqlite 下拉列表示例

让我们看一下使用 sqlite 数据库添加和显示字符串内容的简单代码。

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>  
<RelativeLayout 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"  
    tools:context="example.javatpoint.com.sqlitespinner.MainActivity">  


    <EditText  
        android:id="@+id/input_label"  
        android:layout_width="wrap_content"  
        android:layout_height="wrap_content"  
        android:layout_alignParentTop="true"  
        android:layout_centerHorizontal="true"  
        android:layout_marginTop="46dp"  
        android:hint="Add item"  
        android:ems="10" />  

    <Button  
        android:id="@+id/btn_add"  
        android:layout_width="wrap_content"  
        android:layout_height="wrap_content"  
        android:layout_below="@+id/input_label"  
        android:layout_centerHorizontal="true"  
        android:layout_marginTop="67dp"  
        android:text="Add item" />  

    <Spinner  
        android:id="@+id/spinner"  
        android:layout_width="match_parent"  
        android:layout_height="wrap_content"  
        android:layout_alignParentLeft="true"  
        android:layout_alignParentStart="true"  
        android:layout_below="@+id/btn_add"  
        android:layout_marginTop="70dp" />  
</RelativeLayout>

Activity类

package example.javatpoint.com.sqlitespinner;

import android.content.Context;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.view.inputmethod.InputMethodManager;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.Toast;
import java.util.List;

public class MainActivity extends AppCompatActivity implements AdapterView.OnItemSelectedListener {
    Spinner spinner;
    Button btnAdd;
    EditText inputLabel;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        spinner = findViewById(R.id.spinner);
        btnAdd =  findViewById(R.id.btn_add);
        inputLabel = findViewById(R.id.input_label);

        spinner.setOnItemSelectedListener(this);

        // Loading spinner data from database
        loadSpinnerData();

        btnAdd.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View arg0) {
                String label = inputLabel.getText().toString();

                if (label.trim().length() > 0) {
                    DatabaseHandler db = new DatabaseHandler(getApplicationContext());
                    db.insertLabel(label);

                    // making input filed text to blank
                    inputLabel.setText("");

                    // Hiding the keyboard
                    InputMethodManager imm = (InputMethodManager)
                            getSystemService(Context.INPUT_METHOD_SERVICE);
                    imm.hideSoftInputFromWindow(inputLabel.getWindowToken(), 0);
                    // loading spinner with newly added data
                    loadSpinnerData();
                } else {
                    Toast.makeText(getApplicationContext(), "Please enter label name",
                            Toast.LENGTH_SHORT).show();
                }

            }
        });
    }

    /**
     * Function to load the spinner data from SQLite database
     * */
    private void loadSpinnerData() {
        DatabaseHandler db = new DatabaseHandler(getApplicationContext());
        List labels = db.getAllLabels();

        // Creating adapter for spinner
        ArrayAdapter dataAdapter = new ArrayAdapter(this,android.R.layout.simple_spinner_item, labels);

        // Drop down layout style - list view with radio button
        dataAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);

        // attaching data adapter to spinner
        spinner.setAdapter(dataAdapter);
    }

    @Override
    public void onItemSelected(AdapterView parent, View view, int position,
                               long id) {
        // On selecting a spinner item
        String label = parent.getItemAtPosition(position).toString();

        // Showing selected spinner item
        Toast.makeText(parent.getContext(), "You selected: " + label,
                Toast.LENGTH_LONG).show();

    }

    @Override
    public void onNothingSelected(AdapterView arg0) {
        // TODO Auto-generated method stub

    }
}

数据库处理器类

package example.javatpoint.com.sqlitespinner;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import java.util.ArrayList;
import java.util.List;

public class DatabaseHandler extends SQLiteOpenHelper {
    private static final int DATABASE_VERSION = 1;
    private static final String DATABASE_NAME = "spinnerExample";
    private static final String TABLE_NAME = "labels";
    private static final String COLUMN_ID = "id";
    private static final String COLUMN_NAME = "name";

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

    // Creating Tables
    @Override
    public void onCreate(SQLiteDatabase db) {
        // Category table create query
        String CREATE_ITEM_TABLE = "CREATE TABLE " + TABLE_NAME + "("
                + COLUMN_ID + " INTEGER PRIMARY KEY," + COLUMN_NAME + " TEXT)";
        db.execSQL(CREATE_ITEM_TABLE);
    }

    // Upgrading database
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // Drop older table if existed
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);

        // Create tables again
        onCreate(db);
    }

    /**
     * Inserting new lable into lables table
     * */
    public void insertLabel(String label){
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(COLUMN_NAME, label);//column name, column value

        // Inserting Row
        db.insert(TABLE_NAME, null, values);//tableName, nullColumnHack, CotentValues
        db.close(); // Closing database connection
    }

    /**
     * Getting all labels
     * returns list of labels
     * */
    public List getAllLabels(){
        List list = new ArrayList();

        // Select All Query
        String selectQuery = "SELECT  * FROM " + TABLE_NAME;

        SQLiteDatabase db = this.getReadableDatabase();
        Cursor cursor = db.rawQuery(selectQuery, null);//selectQuery,selectedArguments

        // looping through all rows and adding to list
        if (cursor.moveToFirst()) {
            do {
                list.add(cursor.getString(1));//adding 2nd column data
            } while (cursor.moveToNext());
        }
        // closing connection
        cursor.close();
        db.close();
        // returning lables
        return list;
    }
}

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