基本上，我有一个使用Hashmapping的数据库。 在我运行查询之后，我想输出ID并将其存储在另一个活动的数组中。 之后，我想从数组中访问一个元素。
这是我的数据库代码
public ArrayList<HashMap<String, String>> getIDList() {
ArrayList<HashMap<String, String>> IDList = new ArrayList<HashMap<String, String>>();
String selectQuery = "SELECT cardID FROM flashcards";
SQLiteDatabase database = this.getWritableDatabase();
Cursor cursor = database.rawQuery(selectQuery, null);
if(cursor.moveToFirst()) {
do { HashMap<String, String> cardMap = new HashMap<String, String>();
cardMap.put("cardID", cursor.getString(0));
IDList.add(cardMap);
} while(cursor.moveToNext());
}
return IDList;
这是我尝试访问元素的代码。在这种情况下，我想访问第一个元素。但是错误
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_flashcards_random);
TextView currentID = (TextView) findViewById(R.id.currentIdText);
ArrayList<HashMap<String, String>> IDList = dbTools.getIDList();
currentID.setText((IDList.get(0)).toString());
}
有什么建议吗？
编辑：根据要求提供更多代码。
这是DB Tools代码
package com.izulki.flipper;
import java.util.ArrayList;
import java.util.HashMap;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class DBTools extends SQLiteOpenHelper {
public DBTools(Context applicationContext){
super(applicationContext, "flashcards.db", null, 1);
}
String DBName = "flashcards";
@Override
public void onCreate(SQLiteDatabase database) {
String query = "CREATE TABLE flashcards (cardID INTEGER PRIMARY KEY, question VARCHAR, answer VARCHAR, subject VARCHAR, answered INTEGER, correct INTEGER)";
database.execSQL(query);
}
@Override
public void onUpgrade(SQLiteDatabase database, int oldVersiom, int newVersion) {
String query = "DROP TABLE IF EXISTS flashcards";
database.execSQL(query);
onCreate(database);
}
public boolean checkCard(String CardID) {
SQLiteDatabase database = this.getReadableDatabase();
Cursor cursor = database.rawQuery("SELECT * FROM flashcards WHERE CardID = ? ", new String[]{CardID});
boolean exists = (cursor.getCount() > 0);
cursor.close();
return exists;
}
public void insertCard(HashMap<String, String> queryValues) {
SQLiteDatabase database = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put("question", queryValues.get("question"));
values.put("answer", queryValues.get("answer"));
values.put("subject", queryValues.get("subject"));
values.put("answered", 0);
values.put("correct", 0);
database.insert("flashcards", null, values);
database.close();
}
public int getCardsCount() {
String countQuery = "SELECT * FROM flashcards";
SQLiteDatabase flashcards = this.getReadableDatabase();
Cursor cursor = flashcards.rawQuery(countQuery, null);
int cnt = cursor.getCount();
cursor.close();
return cnt;
}
public int updateCard(HashMap<String, String> queryValues) {
SQLiteDatabase database = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put("question", queryValues.get("question"));
values.put("answer", queryValues.get("answer"));
values.put("subject", queryValues.get("subject"));
return database.update("flashcards", values,
"cardID" + " =?", new String[] {queryValues.get("cardID")});
}
public void resetCardStatistics(int cardID) {
SQLiteDatabase database = this.getWritableDatabase();
String resetQuery = "UPDATE flashcards SET answered = 0, correct = 0 WHERE CardID ='" + cardID + "'";
database.execSQL(resetQuery);
}
public void deleteAllCards() {
SQLiteDatabase database = this.getWritableDatabase();
String deleteQuery = "Delete FROM flashcards";
database.execSQL(deleteQuery);
}
public void deleteCard(int cardID) {
SQLiteDatabase database = this.getWritableDatabase();
String deleteQuery = "DELETE FROM flashcards WHERE CardID ='" + cardID + "'";
database.execSQL(deleteQuery);
}
public ArrayList<HashMap<String, String>> getAllCards(){
ArrayList<HashMap<String, String>> cardArrayList = new ArrayList<HashMap<String, String>>();
String selectQuery = "SELECT * FROM flashcards ORDER BY subject";
SQLiteDatabase database = this.getWritableDatabase();
Cursor cursor = database.rawQuery(selectQuery, null);
if(cursor.moveToFirst()){
do{
HashMap<String, String> cardMap = new HashMap<String, String>();
cardMap.put("cardID", cursor.getString(0));
cardMap.put("question", cursor.getString(1));
cardMap.put("answer", cursor.getString(2));
cardMap.put("subject", cursor.getString(3));
cardArrayList.add(cardMap);
} while(cursor.moveToNext());
}
return cardArrayList;
}
public ArrayList<HashMap<String, String>> getCardsSubject(String subjectSearch) {
ArrayList<HashMap<String, String>> subjectList = new ArrayList<HashMap<String, String>>();
String selectQuery = "SELECT cardID FROM flashcards WHERE subject = '" + subjectSearch + "'";
SQLiteDatabase database = this.getWritableDatabase();
Cursor cursor = database.rawQuery(selectQuery, null);
if(cursor.moveToFirst()) {
do { HashMap<String, String> cardMap = new HashMap<String, String>();
cardMap.put("cardID", cursor.getString(0));
subjectList.add(cardMap);
} while(cursor.moveToNext());
}
return subjectList;
}
public ArrayList<HashMap<String, String>> getIDList() {
ArrayList<HashMap<String, String>> IDList = new ArrayList<HashMap<String, String>>();
String selectQuery = "SELECT cardID FROM flashcards";
SQLiteDatabase database = this.getWritableDatabase();
Cursor cursor = database.rawQuery(selectQuery, null);
if(cursor.moveToFirst()) {
do { HashMap<String, String> cardMap = new HashMap<String, String>();
cardMap.put("cardID", cursor.getString(0));
IDList.add(cardMap);
} while(cursor.moveToNext());
}
return IDList;
}
public HashMap<String, String> getQuestionFromID(int randomID) {
HashMap<String, String> questionFinal = new HashMap<String, String>();
SQLiteDatabase database = this.getReadableDatabase();
String selectQuery = "SELECT question FROM flashcards WHERE cardID ='" + randomID + "'";
Cursor cursor = database.rawQuery(selectQuery, null);
if (cursor.moveToFirst()) {
do{
questionFinal.put("question", cursor.getString(0));
} while (cursor.moveToNext());
}
return questionFinal;
}
public HashMap<String, String> getAnswerFromID(int randomID) {
HashMap<String, String> answerFinal = new HashMap<String, String>();
SQLiteDatabase database = this.getReadableDatabase();
String selectQuery = "SELECT answer FROM flashcards WHERE cardID ='" + randomID + "'";
Cursor cursor = database.rawQuery(selectQuery, null);
if (cursor.moveToFirst()) {
do{
answerFinal.put("answer", cursor.getString(0));
} while (cursor.moveToNext());
}
return answerFinal;
}
public void incrementCorrect(int ID){
SQLiteDatabase database = this.getWritableDatabase();
String incrementQuery = "UPDATE flashcards SET correct = correct +1 WHERE CardID = '" + ID + "'" ;
database.execSQL(incrementQuery);
}
public void incrementAnswered(int randomID) {
SQLiteDatabase database = this.getWritableDatabase();
String incrementQuery = "UPDATE flashcards SET answered = answered +1 WHERE CardID = '" + randomID + "'" ;
database.execSQL(incrementQuery);
}
public HashMap<String, String> getCardInfo(int randomID){
HashMap<String, String> cardMap = new HashMap<String, String>();
SQLiteDatabase database = this.getReadableDatabase();
String selectQuery = "SELECT * FROM flashcards WHERE cardID ='" + randomID + "'";
Cursor cursor = database.rawQuery(selectQuery, null);
if(cursor.moveToFirst()){
do{
cardMap.put("cardID", cursor.getString(0));
cardMap.put("question", cursor.getString(1));
cardMap.put("answer", cursor.getString(2));
cardMap.put("subject", cursor.getString(3));
cardMap.put("answered", cursor.getString(4));
cardMap.put("correct", cursor.getString(5));
} while(cursor.moveToNext());
}
return cardMap;
}
}
这是活动代码
package com.izulki.flipper;
import java.util.ArrayList;
import java.util.HashMap;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.widget.TextView;
import android.widget.Toast;
public class FlashcardsAnswer extends Activity {
DBTools dbTools = new DBTools(this);
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_flashcards_random);
TextView currentID = (TextView) findViewById(R.id.currentIdText);
ArrayList<HashMap<String, String>> IDList = dbTools.getIDList();
currentID.setText((IDList.get(0)).toString());
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.flashcards_answer, menu);
return true;
}
}
这就是错误
02-21 15:02:55.777: E/AndroidRuntime(1827): FATAL EXCEPTION: main
02-21 15:02:55.777: E/AndroidRuntime(1827): java.lang.RuntimeException: Unable to instantiate application android.app.Application: java.lang.IllegalStateException: Unable to get package info for com.izulki.flipper; is package not installed?
02-21 15:02:55.777: E/AndroidRuntime(1827): at android.app.LoadedApk.makeApplication(LoadedApk.java)
02-21 15:02:55.777: E/AndroidRuntime(1827): at android.app.ActivityThread.handleBindApplication(ActivityThread.java)
02-21 15:02:55.777: E/AndroidRuntime(1827): at android.app.ActivityThread.access$1300(ActivityThread.java)
02-21 15:02:55.777: E/AndroidRuntime(1827): at android.app.ActivityThread$H.handleMessage(ActivityThread.java)
02-21 15:02:55.777: E/AndroidRuntime(1827): at android.os.Handler.dispatchMessage(Handler.java)
02-21 15:02:55.777: E/AndroidRuntime(1827): at android.os.Looper.loop(Looper.java)
02-21 15:02:55.777: E/AndroidRuntime(1827): at android.app.ActivityThread.main(ActivityThread.java)
02-21 15:02:55.777: E/AndroidRuntime(1827): at java.lang.reflect.Method.invokeNative(Native Method)
02-21 15:02:55.777: E/AndroidRuntime(1827): at java.lang.reflect.Method.invoke(Method.java)
02-21 15:02:55.777: E/AndroidRuntime(1827): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java)
02-21 15:02:55.777: E/AndroidRuntime(1827): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java)
02-21 15:02:55.777: E/AndroidRuntime(1827): at dalvik.system.NativeStart.main(Native Method)
02-21 15:02:55.777: E/AndroidRuntime(1827): Caused by: java.lang.IllegalStateException: Unable to get package info for com.izulki.flipper; is package not installed?
02-21 15:02:55.777: E/AndroidRuntime(1827): at android.app.LoadedApk.initializeJavaContextClassLoader(LoadedApk.java)
02-21 15:02:55.777: E/AndroidRuntime(1827): at android.app.LoadedApk.getClassLoader(LoadedApk.java)
02-21 15:02:55.777: E/AndroidRuntime(1827): ... 12 more
答案 0 :(得分：6)
试试这个：
for (HashMap<String, String> map : IDList)
for (Entry<String, String> mapEntry : map.entrySet())
{
String key = mapEntry.getKey();
String value = mapEntry.getValue();
}
对于单个元素：IDList.get(0).get(key);