更新SQLite数据库数据

本文所有代码均存放于
https://github.com/MADMAX110/Starbuzz
之前了解了如何修改应用让它从SQLite数据库中提取数据，但是还没有用过更新过数据库数据。
这里要修改应用使用户能够记录哪些饮料是他们的最爱。为此要为DrinkActivity增加一个复选框；
如果选中这个复选框，就说明当前饮料是用户的一个最爱。
还要为TopLevelActivity增加一个新的列表视图，其中包含用户最喜欢的饮料。

一、更新DrinkActivity

在之前的数据库中已经为DRINK表增加了一个FAVORITE列，下面要让用这个列让用户指示某个饮料是否是他的一个最爱。我们会在一个新的复选框中显示这个值，用户单击这个复选框时要用这个新值更新FAVORITE列。

1、向DrinkActivity的布局增加一个复选框

先增加一个字符串资源

    <string name="favorite">Favoritestring>

在activity_drink.xml中增加一个复选框

    <CheckBox
        android:id = "@+id/favorite"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/favorite"
        android:onClick="onFavoriteClicked"/>

要使返回的数据包含FAVORITE列，只需要把FAVORITE列增加到游标返回的列名数组。

Cursor cursor = db.query("DRINK",
		new String[]{"NAME", "DESCRIPTION", "IMAGE_RESOURCE_ID", "FAVORITE"},
		"_id = ?",
		new String[] {Integer.toString(drinkId)},
		null, null, null);

有了FAVORITE这个列的值后，就可以相应的更新favorite复选框。要得到这个值，首先导航到游标的第一个（也是唯一一个记录）。

cursor.moveToFirst()

然后得到当前饮料的FAVORITE列的值。FAVORITE列包含数值0和1。
1就选中复选框，0就不选中复选框：

boolean isFavorite = (cursor.getInt(3) == 1);
                CheckBox favorite = (CheckBox) findViewById(R.id.favorite);
                favorite.setChecked(isFavorite);

响应单击事件来更新数据库。

2、完整的DrinlkActivity代码

package com.hfad.starbuzz;

import androidx.appcompat.app.AppCompatActivity;

import android.content.ContentValues;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.os.Bundle;
import android.view.View;
import android.widget.CheckBox;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;

public class DrinkActivity extends AppCompatActivity {

    public static final String EXTRA_DRINKID = "drinkId";

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

        int drinkId = (Integer)getIntent().getExtras().get(EXTRA_DRINKID);

        SQLiteOpenHelper starbuzzDatabaseHelper = new StarbuzzDatabaseHelper(this);
        try {
            SQLiteDatabase db = starbuzzDatabaseHelper.getReadableDatabase();
            Cursor cursor = db.query("DRINK",
                    new String[]{"NAME", "DESCRIPTION", "IMAGE_RESOURCE_ID", "FAVORITE"},
                    "_id = ?",
                    new String[] {Integer.toString(drinkId)},
                    null, null, null);
            if (cursor.moveToFirst()) {
                String nameText = cursor.getString(0);
                String descriptionText = cursor.getString(1);
                int photoId = cursor.getInt(2);
                boolean isFavorite = (cursor.getInt(3) == 1);

                TextView name = (TextView) findViewById(R.id.name);
                name.setText(nameText);

                TextView description = (TextView) findViewById(R.id.description);
                description.setText(descriptionText);

                ImageView photo = (ImageView) findViewById(R.id.photo);
                photo.setImageResource(photoId);
                photo.setContentDescription(nameText);

                CheckBox favorite = (CheckBox) findViewById(R.id.favorite);
                favorite.setChecked(isFavorite);
            }
            cursor.close();
            db.close();
        }catch (SQLException e){
            Toast toast = Toast.makeText(this,
                    "Database unavailable",
                    Toast.LENGTH_SHORT);
            toast.show();
        }
    }

    public void onFavoriteClicked(View view){
        int drinkId = (Integer)getIntent().getExtras().get(EXTRA_DRINKID);

        CheckBox favorite = (CheckBox) findViewById(R.id.favorite);
        ContentValues drinkValues = new ContentValues();
        drinkValues.put("FAVORITE", favorite.isChecked());

        SQLiteOpenHelper starbuzzDatabaseHelper = new StarbuzzDatabaseHelper(this);
        try{
            SQLiteDatabase db = starbuzzDatabaseHelper.getWritableDatabase();
            db.update("DRINK",
                    drinkValues,
                    "_id = ?",
                    new String[] {Integer.toString(drinkId)});
            db.close();
        }catch(SQLiteException e) {
            Toast toast = Toast.makeText(this, "Database unavailable", Toast.LENGTH_SHORT);
            toast.show();
        }
    }

}

二、在TopLevelActivity中显示用户的最爱

1、为TopLevelActivity的布局增加一个列表视图和一个文本视图
2、填充列表视图，并让它响应单击事件
3、选择一个新的最爱饮料时刷新列表视图数据

1、更新activity_top_level.xml

先增加字符串

  <string name="favorites">Your favorite drinks:string>

再在activity_top_level.xml中增加一个列表视图和文本视图

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="@string/favorites" />

    <ListView
        android:id="@+id/list_favorites"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"/>

2、更新TopLevelActivity

package com.hfad.starbuzz;

import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.CursorAdapter;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;
import android.widget.Toast;

public class TopLevelActivity extends AppCompatActivity {

    private SQLiteDatabase db;
    private Cursor favoritesCursor;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_top_level);
        setupOptionsListView();
        setupFavoritesListView();
    }

    private void setupOptionsListView() {
        //创建监听器
        AdapterView.OnItemClickListener itemClickListener =
                new AdapterView.OnItemClickListener() {
                    @Override
                    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                        //Drink是列表视图中的第一项，所以位于位置0
                        if (position == 0) {
                            //这个意图来自TopLevelActivity,需要启动DrinkCategoryActivity
                            Intent intent = new Intent(TopLevelActivity.this, DrinkCategoryActivity.class);
                            startActivity(intent);
                        }
                    }
                };
        //为列表视图增加监听器
        ListView listView = (ListView) findViewById(R.id.list_options);
        listView.setOnItemClickListener(itemClickListener);
    }

    private void setupFavoritesListView() {
        ListView listFavorites = (ListView) findViewById(R.id.list_favorites);
        try{
            SQLiteOpenHelper starbuzzDatabaseHelper = new StarbuzzDatabaseHelper(this);
            db = starbuzzDatabaseHelper.getReadableDatabase();
            favoritesCursor = db.query("DRINK",
                    new String[]{"_id", "NAME"},
                    "FAVORITE = 1",
                    null, null, null, null);
            CursorAdapter favoriteAdapter = new SimpleCursorAdapter(TopLevelActivity.this,
                    android.R.layout.simple_list_item_1,
                    favoritesCursor,
                    new String[]{"NAME"},
                    new int[]{android.R.id.text1}, 0);
            listFavorites.setAdapter(favoriteAdapter);
        }catch (SQLiteException e){
            Toast.makeText(this, "Database unavailable", Toast.LENGTH_SHORT).show();
        }

        listFavorites.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int i, long id) {
                Intent intent = new Intent(TopLevelActivity.this, DrinkActivity.class);
                intent.putExtra(DrinkActivity.EXTRA_DRINKID, (int)id);
                startActivity(intent);
            }
        });
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        favoritesCursor.close();
        db.close();
    }
}

3、游标不会自动刷新

如果用户导航到DrinkActivity来选择一个新的最爱饮料。这个新的最爱饮料不会自动显示在TopLevelActivity的list_favorites列表视图中。这是因为游标只在创建时获取数据。
需要使用changeCursor方法改变游标
向DrinkActivity中添加onRestart即可：

    @Override
    protected void onRestart() {
        super.onRestart();
        Cursor newCursor = db.query("DRINK",
                new String[]{"_id", "NAME"},
                "FAVORITE = 1",
                null, null, null, null);
        ListView listFavorites = (ListView) findViewById(R.id.list_favorites);
        CursorAdapter adapter = (CursorAdapter) listFavorites.getAdapter();
        adapter.changeCursor(newCursor);
        favoritesCursor = newCursor;
    }