java– 如何创建新活动,我可以选择从数据库中添加新项目？

概述我在this教程之后创建了数据库,并且我在主活动中创建了一个按钮,该按钮将用户带到另一个活动,在那里他们将添加一些新项目.但我不知道如何使用ArrayList执行此 *** 作,因为我想在ListView中添加新项目.我希望在我的应用程序中有类似this的东西.任何帮助都会被贬低.这是DataBase的代码

我在this教程之后创建了数据库,并且我在主活动中创建了一个按钮,该按钮将用户带到另一个活动,在那里他们将添加一些新项目.但我不知道如何使用ArrayList执行此 *** 作,因为我想在ListVIEw中添加新项目.我希望在我的应用程序中有类似this的东西.任何帮助都会被贬低.

这是DataBase的代码：

    public class DatabaseHandler extends sqliteOpenHelper {    // All Static variables    // Database Version    private static final int DATABASE_VERSION = 1;    // Database name    private static final String DATABASE_name = "itemmanager";    // Contacts table name    private static final String table_ITEMS = "items";    // Contacts table Columns names    private static final String KEY_ID = "ID";    private static final String KEY_Title = "Title";    private static final String KEY_PRICE = "price";    public DatabaseHandler(Context context) {        super(context, DATABASE_name, null, DATABASE_VERSION);    }    // Creating tables    @OverrIDe    public voID onCreate(sqliteDatabase db) {        String CREATE_ITEMS_table = "CREATE table " + table_ITEMS + "("                + KEY_ID + " INTEGER PRIMARY KEY," + KEY_Title + " TEXT,"                + KEY_PRICE + " TEXT" + ")";        db.execsql(CREATE_ITEMS_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_ITEMS);        // Create tables again        onCreate(db);    }    /**     * All CRUD(Create, Read, Update, Delete) Operations     */    // Adding new item    voID addItem(Item item) {        sqliteDatabase db = this.getWritableDatabase();        ContentValues values = new ContentValues();        values.put(KEY_Title, item.getTitle()); // Title name        values.put(KEY_PRICE, item.getPrice()); // Price        // Inserting Row        db.insert(table_ITEMS, null, values);        db.close(); // Closing database connection    }    // Getting item    Item getItem(int ID) {        sqliteDatabase db = this.getReadableDatabase();        Cursor cursor = db.query(table_ITEMS, new String[] { KEY_ID,                KEY_Title, KEY_PRICE }, KEY_ID + "=?",                new String[] { String.valueOf(ID) }, null, null, null, null);        if (cursor != null)            cursor.movetoFirst();        Item item = new Item(Integer.parseInt(cursor.getString(0)),                cursor.getString(1), cursor.getString(2));        // return item        return item;    }    // Getting All Items    public List<Item> getAllitems() {        List<Item> itemsList = new ArrayList<Item>();        // Select All query        String selectquery = "SELECT  * FROM " + table_ITEMS;        sqliteDatabase db = this.getWritableDatabase();        Cursor cursor = db.rawquery(selectquery, null);        // looPing through all rows and adding to List        if (cursor.movetoFirst()) {            do {                Item item = new Item();                item.setID(Integer.parseInt(cursor.getString(0)));                item.setTitle(cursor.getString(1));                item.setPrice(cursor.getString(2));                // Adding contact to List                itemsList.add(item);            } while (cursor.movetoNext());        }        // return items List        return itemsList;    }    // Updating single item    public int updateItem(Item item) {        sqliteDatabase db = this.getWritableDatabase();        ContentValues values = new ContentValues();        values.put(KEY_Title, item.getTitle());        values.put(KEY_PRICE, item.getPrice());        // updating row        return db.update(table_ITEMS, values, KEY_ID + " = ?",                new String[] { String.valueOf(item.getID()) });    }    // Deleting single item    public voID deleteItem(Item item) {        sqliteDatabase db = this.getWritableDatabase();        db.delete(table_ITEMS, KEY_ID + " = ?",                new String[] { String.valueOf(item.getID()) });        db.close();    }    // Getting items Count    public int getItemsCount() {        String countquery = "SELECT  * FROM " + table_ITEMS;        sqliteDatabase db = this.getReadableDatabase();        Cursor cursor = db.rawquery(countquery, null);        cursor.close();        // return count        return cursor.getCount();    }}    

这是MainActivity的代码：

    public class MainActivity extends BaseActivity {    button addItem;    private Toolbar toolbar;    @OverrIDe    public voID onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        FrameLayout frameLayout = (FrameLayout)findVIEwByID(R.ID.frame_container);         // inflate the custom activity layout        LayoutInflater layoutInflater = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);        VIEw activityVIEw = layoutInflater.inflate(R.layout.activity_main, null,false);        frameLayout.addVIEw(activityVIEw);        // Setting toolbar        toolbar = (Toolbar) findVIEwByID(R.ID.app_bar);        setSupportActionbar(toolbar);        getSupportActionbar().setdisplayHomeAsUpEnabled(true);        getSupportActionbar().setHomebuttonEnabled(true);        DatabaseHandler db = new DatabaseHandler(this);        addItem = (button) findVIEwByID(R.ID.button1);        addItem.setonClickListener(new VIEw.OnClickListener() {            @OverrIDe            public voID onClick(VIEw v) {                Intent intent = new Intent(MainActivity.this, AddActivity.class);                startActivity(intent);            }        });    }}

这是我的主要活动布局：

    <relativeLayout xmlns:androID="http://schemas.androID.com/apk/res/androID"    androID:ID="@+ID/mainContent"    androID:layout_wIDth="wrap_content"    androID:layout_height="wrap_content" >    <include        androID:ID="@+ID/app_bar"        layout="@layout/app_bar" />    <button        androID:ID="@+ID/button1"                androID:layout_wIDth="match_parent"        androID:layout_height="wrap_content"        androID:layout_alignParentBottom="true"        androID:text="@string/button" />    <ListVIEw        androID:ID="@+ID/List"        androID:layout_margin="5dp"        androID:layout_below="@+ID/relativeLayout"        androID:layout_wIDth="fill_parent"        androID:layout_height="wrap_content"        androID:layout_above="@+ID/button1"        androID:layout_centerHorizontal="true"        androID:divIDer="@color/List_divIDer_row"        androID:divIDerHeight="10.0sp"        androID:ListSelector="@drawable/List_row_selector" >    </ListVIEw>    <relativeLayout        androID:ID="@+ID/relativeLayout"        androID:layout_wIDth="wrap_content"        androID:layout_height="wrap_content"        androID:layout_alignleft="@+ID/ListVIEw1"        androID:layout_alignRight="@+ID/ListVIEw1"        androID:layout_below="@+ID/app_bar"        androID:padding="10dp" >        <TextVIEw            androID:ID="@+ID/item_text"            androID:layout_wIDth="wrap_content"            androID:layout_height="wrap_content"            androID:layout_alignParentleft="true"            androID:layout_alignParenttop="true"            androID:layout_marginleft="10dp"            androID:layout_margintop="4dp"            androID:text="Items"            androID:textcolor="#474747"            androID:textSize="16sp" />        <TextVIEw            androID:ID="@+ID/item_count"            androID:layout_wIDth="wrap_content"            androID:layout_height="wrap_content"            androID:layout_alignParenttop="true"            androID:layout_marginleft="5dp"            androID:layout_margintop="4dp"            androID:layout_toRightOf="@+ID/item_text"            androID:text="(2)"            androID:textcolor="#474747"            androID:textSize="14sp" />        <TextVIEw            androID:ID="@+ID/total_amount"            androID:layout_wIDth="wrap_content"            androID:layout_height="wrap_content"            androID:layout_alignParentRight="true"            androID:layout_centerVertical="true"            androID:text="Rs. 5700"            androID:textcolor="#000000"            androID:textSize="20dp" />    </relativeLayout></relativeLayout>

解决方法:

简而言之,您需要传递将项目添加回主要活动的“结果”.然后,如果添加了项目,则应调用适配器以更新适配器数据.

 // Your prevIoUs code       addItem = (button) findVIEwByID(R.ID.button1);        addItem.setonClickListener(new VIEw.OnClickListener() {            @OverrIDe             public voID onClick(VIEw v) {                Intent intent = new Intent(MainActivity.this, AddActivity.class);                startActivityForResult(intent, ADD_ITEM_REQ_CODE);            }         }); // Then handle the resultpublic voID onActivityResult(int reqCode, int resultCode, Intent data){  if (reqCode == ADD_ITEM_REQ_CODE && resultCode == RESulT_OK){    // get your ListVIEw adapter and update data    mlistadapter.notifyDataSetChanged();  }}

第二个活动,添加项目的活动应该在成功添加项目时调用setResult(RESulT_OK),否则调用setResult(RESulT_CANCELLED).

您的代码还有其他一些功能,例如,您在哪里填充ListVIEw？通常,您可以通过findVIEwByID获取实例,并使用相应的数据为该ListVIEw设置适配器.

老实说,我认为你应该再看看这些教程,特别是这些：
http://developer.android.com/training/basics/intents/result.html
http://developer.android.com/guide/topics/ui/layout/listview.html

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