我是
Android框架的新手,我无法通过sqlite获得第一个基础.
我正在尝试构建一个非常简单的应用程序,其中包含一个EditText搜索框,当按下某个键时,会在sqlite数据库上执行Like％word％搜索,以查找在EditText框中输入的文本,并将结果显示在列表显示.
注：下面的代码包括调试和注释代码,抱歉,我还没有完成清理它.
激活是
public class sustainable_fish extends Activity {
private String keycodeToAscii(int arg2){
String retvar = "";
switch(arg2){
case KeyEvent.KEYCODE_A: retvar = "a";break;
case KeyEvent.KEYCODE_B: retvar = "b";break;
剪掉了,但你明白了.
case KeyEvent.KEYCODE_RIGHT_BRACKET: retvar = ")";break;
default: retvar = ""; break;
};
return retvar;
}
Context that = getApplicationContext();
fishDB dh = new fishDB(getApplicationContext());
private OnKeyListener search = new OnKeyListener() {
public boolean onKey(View arg0,int arg1,KeyEvent arg2) {
@SuppressWarnings("unused")
Cursor cur = null;
String searchData;
EditText myEditText = (EditText) findViewById(R.id.fish_search);
CharSequence edit_text_value = myEditText.getText();
searchData = edit_text_value.toString();
searchData = searchData + keycodeToAscii(arg2.getKeyCode() );
Log.d("onKey","searchData = "+searchData);
/*
Commented out because as the database doesn't work,so theirs no point just yet searching.
cur = fish.search(searchData);
if (cur != null)
{
String[] displayFields = new String[] {cur.getString(2),cur.getString(1)};
int[] displayViews = new int[] { R.id.fish_rank,R.id.fish_name};
SimpleCursorAdapter adapter = new SimpleCursorAdapter(that,R.layout.text_list,cur,displayFields,displayViews);
ListView myList=(ListView)findViewById(android.R.id.list);
myList.setAdapter(adapter);
}
*/
return false;
}
};
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
EditText searchBar = (EditText) findViewById(R.id.fish_search);
searchBar.setOnKeyListener(search);
}
}
public class fishDB {
public static final String DATABASE_NAME = "fish.db3";
public static final int DATABASE_VERSION = 1;
private sqliteDatabase database;
private Context myContext;
private static boolean booFirstrun = false;
fishDB(Context inContext){
myContext = inContext;
OpenHelper helper = new OpenHelper(myContext);
Log.w("fishDB","Called OpenHelper");
// Here be the problem...
database = helper.getWritableDatabase();
}
public boolean firstRun(){
return booFirstrun;
}
private static class OpenHelper extends sqliteOpenHelper {
private static final String CREATE_TABLE_FeedS = "create table Feeds (Feed_id integer primary key autoincrement,"
+ "title text not null,url text not null);";
OpenHelper(Context context) {
super(context,DATABASE_NAME,null,DATABASE_VERSION);
Log.w("OpenHelper","Called superconstructor");
}
@Override
public void onCreate(sqliteDatabase db) {
try {
Log.w("OpenHelper","in onCreate");
booFirstrun = true;
Log.w("OpenHelper","set booFirstrun");
db.beginTransaction();
Log.w("OpenHelper","db.beginTransaction");
try {
// Create tables and test data
db.execsql(CREATE_TABLE_FeedS);
Log.w("OpenHelper","execsql");
db.setTransactionSuccessful();
Log.w("OpenHelper","setTransactionSuccessful");
} catch (sqlException e) {
Log.e("Error creating tables and debug data",e.toString());
throw e;
} finally {
db.endTransaction();
}
} catch (Exception e) {
Log.e("OpenHelper",e.toString() );
} finally {
Log.w("OpenHelper","out of onCreate");
}
}
@Override
public void onUpgrade(sqliteDatabase db,int oldVersion,int newVersion) {
Log.w("OpenHelper","Upgrading database,this will drop tables and recreate.");
onCreate(db);
}
}
}
现在每次“database = helper.getWritableDatabase();”被称为应用程序崩溃与NullPointerException.我设法将错误跟踪到OpenHelper的onCreate方法和“db.beginTransaction();”线.
我错过了什么？
解决方法
实际上,您不需要在帮助程序的onCreate方法上启动事务.尝试从除db.execsql(CREATE_TABLE_FeedS)之外的方法中删除所有内容;
更新：我能够重复这个问题.
在该错误消失后,将fishDb字段初始化移动到活动的onCreate()方法.看起来在调用onCreate之前启动数据库初始化并不是一个好主意.
而不是
fishDB fishDb = new fishDB(getApplicationContext());
做
fishDB fishDb;
onCreate(){
super.onCreate();
fishDb = new fishDB(getApplicationContext());
.... //init listener,query db etc..
}
