android学习小结3

1 activity可以继承扩展 ListActivity
 比如：
class DummyNote extends ListActivity {
 private String[] note_array = {
      
            "gasolin",
            "crota",
            "louk",
            "magicion"
          
    };
  ListAdapter adapter = new ArrayAdapter<String>(this,
                    android.R.layout.simple_list_item_1,
                    note_array);
        setListAdapter(adapter);

}

2 使用sqlite
  在新建立工程后，打开模拟器后，在sdk的tools下
运行adb shell
cd data/data/
ls
 cd 工程名
mkdir databases
cd databases
sqlite3 notes.db （建立了一个notes.db数据库）
create talbe notes
......;
sqlite>.databases  (查看当前目录下的数据库列表）
sqllite>.tables  (查看所有数据表）
     .schema notes (查看指定表的结构）
离开sqllite:  .exit

3  CRUD的典型例子
 public class NotesDbAdapter {
 
 private static final String DATABASE_NAME = "notes.db";
    private static final int DATABASE_VERSION = 1;

    private static final String DATABASE_TABLE = "notes";

    private static final String DATABASE_CREATE =
    "create table notes("
        +"_id INTEGER PRIMARY KEY,"
        +"note TEXT,"
        +"created INTEGER,"
        +"modified INTEGER"
    +");";

 private static class DatabaseHelper extends SQLiteOpenHelper {

  public DatabaseHelper(Context context) {
   super(context, DATABASE_NAME, null, DATABASE_VERSION);
   // TODO Auto-generated constructor stub
  }

  @Override
  public void onCreate(SQLiteDatabase db) {
   // TODO Auto-generated method stub
   db.execSQL(DATABASE_CREATE);
  }

  @Override
  public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
   // TODO Auto-generated method stub
   db.execSQL("DROP TABLE IF EXISTS "+DATABASE_TABLE);
   onCreate(db);
  }

    }
 
    private Context mCtx = null;
    private DatabaseHelper dbHelper ;
    private SQLiteDatabase db;

    /** Constructor */
    public NotesDbAdapter(Context ctx) {
        this.mCtx = ctx;
    }

    public NotesDbAdapter open () throws SQLException {
        dbHelper = new DatabaseHelper(mCtx);
        db = dbHelper.getWritableDatabase();
        return this;
    }

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

    //start query
    public static final String KEY_ROWID = "_id";
    public static final String KEY_NOTE = "note";
    public static final String KEY_CREATED = "created";

    String[] strCols = new String[] {
        KEY_ROWID,
        KEY_NOTE,
        KEY_CREATED
    };

    /*
    public Cursor getall() {
        return db.rawQuery("SELECT * FROM notes", null);
    }
    */
   
    /*
    // get all entries
    public Cursor getall() {
        return db.query(DATABASE_TABLE, //Which table to Select
             strCols,// Which columns to return
             null, // WHERE clause
             null, // WHERE arguments
             null, // GROUP BY clause
             null, // HAVING clause
             null //Order-by clause
             );
    }
    */
   
    // get all entries
    public Cursor getall() {
        return db.query(DATABASE_TABLE,
            new String[] {KEY_ROWID, KEY_NOTE, KEY_CREATED},
            null, null, null, null, null);
    }

    // add an entry
    public long create(String Note) {
        Date now = new Date();
        ContentValues args = new ContentValues();
        args.put(KEY_NOTE, Note);
        args.put(KEY_CREATED, now.getTime());

        return db.insert(DATABASE_TABLE, null, args);
    }

    //remove an entry
    public boolean delete(long rowId) {
        return db.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowId, null) > 0;
    }
   
    //query single entry
    public Cursor get(long rowId) throws SQLException {
        Cursor mCursor = db.query(true,
                DATABASE_TABLE,
                new String[] {KEY_ROWID, KEY_NOTE, KEY_CREATED},
                KEY_ROWID + "=" + rowId,
                null, null, null, null, null);
        if (mCursor != null) {
            mCursor.moveToFirst();
        }
        return mCursor;
    }

    //update
    public boolean update(long rowId, String note) {
        ContentValues args = new ContentValues();
        args.put(KEY_NOTE, note);

        return db.update(DATABASE_TABLE, args, KEY_ROWID + "=" + rowId, null) > 0;
    }

}

主程序调用：
    private NotesDbAdapter mDbHelper;
    private Cursor mNotesCursor;
   
    private void setAdapter() {
     mDbHelper = new NotesDbAdapter(this);
        mDbHelper.open();
        fillData();

}
   private void fillData() {
        mNotesCursor = mDbHelper.getall();
        startManagingCursor(mNotesCursor);

        String[] from = new String[]{"note"};
        int[] to = new int[]{android.R.id.text1};

        // Now create a simple cursor adapter
        SimpleCursorAdapter adapter =
                    new SimpleCursorAdapter(this, android.R.layout.simple_list_item_1, mNotesCursor,

from, to);
        setListAdapter(adapter);
    }
   
新增记录：
   public long create(String Note) {
        Date now = new Date();
        ContentValues args = new ContentValues();
        args.put(KEY_NOTE, Note);
       。。。。。。

        return db.insert(DATABASE_TABLE, null, args);
    }
删除记录：
   public boolean delete(long rowId) {
        return db.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowId, null) > 0;
    }
  mDbHelper.delete(getListView().getSelectedItemId());//这里用getListView().getSelectedItemId()获得选定

删除哪一条记录

查询记录：
//query single entry
    public Cursor get(long rowId) throws SQLException {
        Cursor mCursor = db.query(true,
                DATABASE_TABLE,
                new String[] {KEY_ROWID, KEY_NOTE, KEY_CREATED},
                KEY_ROWID + "=" + rowId,
                null, null, null, null, null);
        if (mCursor != null) {
            mCursor.moveToFirst();
        }
        return mCursor;
    }
更新记录：
 //update
    public boolean update(long rowId, String note) {
        ContentValues args = new ContentValues();
        args.put(KEY_NOTE, note);

        return db.update(DATABASE_TABLE, args, KEY_ROWID + "=" + rowId, null) > 0;
    }
4 activity中的相关，比如选了A中的记录，然后打开B来编辑，B编辑完后，再返回A。
   首先在B中，接收BUNDLE：
 private void showViews(Bundle savedInstanceState) {
        //mRowId = savedInstanceState != null ? savedInstanceState.getLong(NotesDbAdapter.KEY_ROWID) :

null;
        if (mRowId == null) {
            Bundle extras = getIntent().getExtras();
            mRowId = extras != null ? extras.getLong(NotesDbAdapter.KEY_ROWID) : null;
        }

 //把编辑的数据拿出来
  if (mRowId != null) {
            Cursor note = mDbHelper.get(mRowId);
            startManagingCursor(note);

            field_note.setText(note.getString(
                    note.getColumnIndexOrThrow(NotesDbAdapter.KEY_NOTE)
                ));
        }
  当编辑成功提交后，
     public void onClick(View view) {
                mDbHelper.update(mRowId, field_note.getText().toString());
                setResult(RESULT_OK);
                finish();
   这里的setResult，表示这个activity成功，返回

在调用方中，如果是一个LISTVIEW的列表的话，点某一个列
  protected void onListItemClick(ListView l, View v, int position, long id) {
     super.onListItemClick(l, v, position, id);
     Intent intent = new Intent(this, NoteEdit.class);
     intent.putExtra(NotesDbAdapter.KEY_ROWID, id);
     startActivityForResult(intent, ACTIVITY_EDIT);
 }
   这里的startActivityForResult表示的是要调用另外一个activity，并且要求结果返回
同时：
  protected void onActivityResult(int requestCode, int resultCode,
                                 Intent intent) {
     super.onActivityResult(requestCode, resultCode, intent);
     fillData();
 }

5 长按菜单
    A 在oncreate函数中，注册
     registerForContextMenu(getListView());//说明点listview时会使用长按菜单
   B public void onCreateContextMenu(ContextMenu menu, View v,
   ContextMenuInfo menuInfo) {
  // TODO Auto-generated method stub
  menu.add(0, MENU_DELETE, 0,  "删除记事");
        menu.setHeaderTitle("要怎么处理这个项目");
  super.onCreateContextMenu(menu, v, menuInfo);
 }