Android之SQLiteDatabase使用与特殊情况处理
1、打开数据库失败
static SQLiteDatabase openOrCreateDatabase(String path, CursorFactory factory)失败，
错误提示如下：
android.database.sqlite.SQLiteCantOpenDatabaseException: unknown error (Sqlite code 14): Could not open database, (OS error - 2:No such file or directory)
这是因为path的值不对，应该和当前应用程序的包名目录一致，也就是读写权限。
使用下面几种方法：
1.1、contex.getFileDir().toString() + "/" + db_name;
1.2、context.getDatabasePath(db_name).getPath();
2、建表失败
String sql = "create table " + TB_NAME + "(_id integer primary key autoincrement,"
+ " title varchar(50),"
+ " content varchar(255))";
mDb.execSQL(sql);失败，
错误提示如下：
android.database.sqlite.SQLiteException: table info already exists (Sqlite code 1): , while compiling: create table info(_id integer primary key autoincrement, title varchar(50), content varchar(255)), (OS error - 2:No such file or directory)
数据库表不能重复创建，会出错。
在建表之前可以先删除，再建表，或者表存在，就不需要再创建。
如何判断表是否存在，可以使用以下几种方法：
https://blog.csdn.net/q610098308/article/details/46803689
/**
* 判断某张表是否存在
* @param tabName 表名
* @return
*/
public boolean tabbleIsExist(String tableName){
boolean result = false;
if(tableName == null){
return false;
}
SQLiteDatabase db = null;
Cursor cursor = null;
try {
db = this.getReadableDatabase();
//这里表名可以是Sqlite_master
String sql = "select count(*) as c from "+AppConstant.DataBaseName+" where type ='table' and name ='"+tableName.trim()+"' ";
cursor = db.rawQuery(sql, null);
if(cursor.moveToNext()){
int count = cursor.getInt(0);
if(count>0){
result = true;
}
}
} catch (Exception e) {
// TODO: handle exception
}
return result;
}https://blog.csdn.net/lizhenmingdirk/article/details/17561471
3种方法，判断表是否存在
1）
可以在创建表之前判断，这样就不会重新创建，
create table if not exists Student(name text primary key, code integer);比平时多了if not exists
2）
Cursor cursor = db.rawQuery("select name from sqlite_master where type='table';", null);
while(cursor.moveToNext()){
//遍历出表名
String name = cursor.getString(0);
Log.i("System.out", name);
}3）
String sql = "select count(*) as c from sqlite_master where type ='table' and name ='Student';";
cursor = db.rawQuery(sql, null);
if(cursor.moveToNext()){
int count = cursor.getInt(0);
if(count>0){
result = true;
}
}3、在子线程中进行数据库表的增删改查
Android中不要在主线程做数据库表记录的增删改查，
因为IO操作相对比较耗时，会拖慢UI的响应速度。
4、字符串值最好用单引号
字段值，特别是字符串，一定要加单引号，否则sql语句会将空格做截断处理。
String title = "alpha";
String content = "good boy";
String values = String.format("values(%d, '%s', '%s')", mId++, title, content);
String sql = "insert into info " + values;
mDb.execSQL(sql);5、退出时，需要关闭数据库。
完整代码如下：
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
private static final int MSG_VIEW_CONTENT = 0x01;
private static final String DB_NAME = "sql_test.db";
private static final String TB_NAME = "info";
private ListView mLvInfo;
private InfoAdapter mAdapter;
private int mId = 0;
private List mListInfo;
private SQLiteDatabase mDb = null;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mLvInfo = (ListView) findViewById(R.id.lv_info);
mAdapter = new InfoAdapter(MainActivity.this);
mLvInfo.setAdapter(mAdapter);
View insert = findViewById(R.id.tv_insert);
View update = findViewById(R.id.tv_update);
View query = findViewById(R.id.tv_query);
View delete = findViewById(R.id.tv_delete);
insert.setOnClickListener(this);
update.setOnClickListener(this);
query.setOnClickListener(this);
delete.setOnClickListener(this);
new Handler().postDelayed(new Runnable() {
@Override
public void run() {
openDataBase();
}
}, 500);
}
private void openDataBase() {
String db_name = getDatabasePath(DB_NAME).getPath();
mDb = SQLiteDatabase.openOrCreateDatabase(db_name, null);
createTable();
}
private boolean isTableExists(String tableName) {
boolean isExists = false;
if (mDb != null) {
String sql_query = "select count(*) as c from Sqlite_master where type ='table' and name ='" + tableName + "'";
Cursor cursor = mDb.rawQuery(sql_query, null);
if (cursor != null) {
if (cursor.moveToNext()) {
int count = cursor.getInt(0);
if (count > 0) {
isExists = true;
}
}
}
}
return isExists;
}
private void createTable() {
if (mDb != null) {
if (!isTableExists(TB_NAME)) {
String sql = "create table " + TB_NAME + "(_id integer primary key autoincrement,"
+ " title varchar(50),"
+ " content varchar(255))";
mDb.execSQL(sql);
} else {
queryRecord();
}
}
}
private void insertRecord() {
new Thread(new Runnable() {
@Override
public void run() {
if (mDb != null) {
String title = "alpha";
String content = "good boy";
String values = String.format("values(%d, '%s', '%s')", mId++, title, content);
String sql = "insert into " + TB_NAME + " " + values;
mDb.execSQL(sql);
}
}
}).start();
}
private void updateRecord() {
new Thread(new Runnable() {
@Override
public void run() {
if (mDb != null) {
String title = "beta";
String update = String.format(" set title = '%s' where _id = %d", title, mId > 0 ? mId-1 : mId);
String sql = "update " + TB_NAME + update;
mDb.execSQL(sql);
}
}
}).start();
}
private void queryRecord() {
new Thread(new Runnable() {
@Override
public void run() {
if (mDb != null) {
String sql = "select * from " + TB_NAME;
Cursor cursor = mDb.rawQuery(sql, null);
if (cursor != null) {
if (mListInfo != null) {
mListInfo.clear();
}
while (cursor.moveToNext()) {
int _id = cursor.getInt(0);
String title = cursor.getString(1);
String content = cursor.getString(2);
if (mListInfo == null) {
mListInfo = new ArrayList();
}
mId = _id + 1;
mListInfo.add("_id:" + _id + ",title:" + title + ",content:" + content);
}
mHandler.sendEmptyMessage(MSG_VIEW_CONTENT);
}
}
}
}).start();
}
private void deleteRecord() {
new Thread(new Runnable() {
@Override
public void run() {
if (mDb != null) {
int _id = mId > 0 ? mId-1 : mId;
String delete = String.format(" where _id = %d", _id);
String sql = "delete from " + TB_NAME + delete;
mDb.execSQL(sql);
}
}
}).start();
}
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.tv_insert:
insertRecord();
break;
case R.id.tv_update:
updateRecord();
break;
case R.id.tv_query:
queryRecord();
break;
case R.id.tv_delete:
deleteRecord();
break;
default:
break;
}
}
@Override
protected void onDestroy() {
super.onDestroy();
if (mDb != null && mDb.isOpen()) {
mDb.close();
}
}
private Handler mHandler = new Handler() {
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case MSG_VIEW_CONTENT:
if (mAdapter != null) {
mAdapter.notifyDataSetChanged();
}
break;
default:
break;
}
}
};
class InfoAdapter extends BaseAdapter {
private Context mContext;
private LayoutInflater mInflater;
public InfoAdapter(Context context) {
mContext = context;
mInflater = LayoutInflater.from(mContext);
}
@Override
public int getCount() {
if (mListInfo != null) {
return mListInfo.size();
}
return 0;
}
@Override
public Object getItem(int position) {
if (mListInfo != null) {
return mListInfo.get(position);
}
return null;
}
@Override
public long getItemId(int position) {
return 0;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView == null) {
convertView = mInflater.inflate(R.layout.item_info, parent, false);
}
TextView tvContent = (TextView) convertView.findViewById(R.id.tv_content);
String content = (String) getItem(position);
tvContent.setText(content);
return convertView;
}
}
}