android学习小结4

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);
}

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