从数据库中获取数据时，SQLite的问题 [英] SQLite problems when getting data from the database
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问题描述
我有一个数据库处理器类是这样的：
public class DatabaseHandler extends SQLiteOpenHelper {
private static final int DATABASE_VERSION = 1;
private static final String DATABASE_NAME = "CaseDatabase";
private static final String TABLE_CASES = "cases";
private static final String KEY_ID = "id";
private static final String DATE = "date";
private static final String RIGHTFINGER = "rightFinger";
private static final String LEFTFINGER = "leftFinger";
public DatabaseHandler(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
String CREATE_CONTACTS_TABLE = "CREATE TABLE " + TABLE_CASES + "("
+ KEY_ID + " INTEGER PRIMARY KEY," + DATE + " TEXT,"
+ RIGHTFINGER + " BLOB," + LEFTFINGER +" BLOB" + ")";
db.execSQL(CREATE_CONTACTS_TABLE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS " + TABLE_CASES);
// Create tables again
onCreate(db);
}
public void addContact(Case c) {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(KEY_ID, c.getCaseNumber()); // PCN
values.put(DATE, c.getDate()); // Date
ByteArrayOutputStream out1 = new ByteArrayOutputStream();
c.getLeftIndexFinger().compress(Bitmap.CompressFormat.PNG, 100, out1);
ByteArrayOutputStream out2 = new ByteArrayOutputStream();
c.getRightIndexFinger().compress(Bitmap.CompressFormat.PNG, 100, out2);
values.put(LEFTFINGER, out1.toByteArray()); // LFINGER
values.put("RIGHTFINGER", out2.toByteArray()); //RFINGER
// Inserting Row
db.insert(TABLE_CASES, null, values);
db.close(); // Closing database connection
}
public ArrayList<Case> getAllContacts() {
ArrayList<Case> caseList = new ArrayList<Case>();
// Select All Query
String selectQuery = "SELECT * FROM " + TABLE_CASES;
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
// looping through all rows and adding to list
if (cursor.moveToFirst()) {
do {
Case c = new Case();
c.setCaseNumber(cursor.getString(0));
c.setDate(cursor.getString(1));
byte[] blob1 = cursor.getBlob(cursor.getColumnIndexOrThrow("2"));
Bitmap bmp1 = BitmapFactory.decodeByteArray(blob1, 0,blob1.length);
c.setLeftIndexFinger(bmp1);
byte[] blob2 = cursor.getBlob(cursor.getColumnIndexOrThrow("3"));
Bitmap bmp2 = BitmapFactory.decodeByteArray(blob1, 0,blob2.length);
c.setRightIndexFinger(bmp2);
// Adding contact to list
caseList.add(c);
} while (cursor.moveToNext());
}
// return contact list
return caseList;
}
}
的添加方法效果很好，但是当我尝试打电话给 getAllContacts 方法是这样的：
The add method works perfectly, but when I try to call the getAllContacts method, like this:
public ArrayList<Case> getFromDatabase() {
ArrayList<Case> c = db.getAllContacts();
return c;
}
list = getFromDatabase();
应用崩溃和LogCat中打印出以下内容：
The app crashes and LogCat prints out following:
07-30 12:07:56.570: E/AndroidRuntime(13040): FATAL EXCEPTION: main
在我尝试从数据库中获取记录的方法，就是在比另一个活动添加法
这是我的 getAllContacts 方法：
public ArrayList<Case> getAllContacts() {
ArrayList<Case> caseList = new ArrayList<Case>();
// Select All Query
String selectQuery = "SELECT * FROM " + TABLE_CASES;
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
// looping through all rows and adding to list
if (cursor.moveToFirst()) {
do {
Case c = new Case();
c.setCaseNumber(cursor.getString(0));
c.setDate(cursor.getString(1));
byte[] blob1 = cursor.getBlob(cursor.getColumnIndexOrThrow("2"));
Bitmap bmp1 = BitmapFactory.decodeByteArray(blob1, 0,blob1.length);
c.setLeftIndexFinger(bmp1);
byte[] blob2 = cursor.getBlob(cursor.getColumnIndexOrThrow("3"));
Bitmap bmp2 = BitmapFactory.decodeByteArray(blob1, 0,blob2.length);
c.setRightIndexFinger(bmp2);
// Adding contact to list
caseList.add(c);
} while (cursor.moveToNext());
}
// return contact list
return caseList;
}
LogCat中信息：
LogCat info:
E/AndroidRuntime(15058): FATAL EXCEPTION: main
E/AndroidRuntime(15058): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.package.hello/com.package.hello.History}: java.lang.NullPointerException
E/AndroidRuntime(15058): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1970)
E/AndroidRuntime(15058): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1995)
E/AndroidRuntime(15058): at android.app.ActivityThread.access$600(ActivityThread.java:128)
E/AndroidRuntime(15058): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1161)
E/AndroidRuntime(15058): at android.os.Handler.dispatchMessage(Handler.java:99)
E/AndroidRuntime(15058): at android.os.Looper.loop(Looper.java:137)
E/AndroidRuntime(15058): at android.app.ActivityThread.main(ActivityThread.java:4517)
E/AndroidRuntime(15058): at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime(15058): at java.lang.reflect.Method.invoke(Method.java:511)
E/AndroidRuntime(15058): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:993)
E/AndroidRuntime(15058): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:760)
E/AndroidRuntime(15058): at dalvik.system.NativeStart.main(Native Method)
E/AndroidRuntime(15058): Caused by: java.lang.NullPointerException
E/AndroidRuntime(15058): at com.package.hello.History.getFromDatabase(History.java:153)
E/AndroidRuntime(15058): at com.package.hello.History.onCreate(History.java:49)
E/AndroidRuntime(15058): at android.app.Activity.performCreate(Activity.java:4533)
E/AndroidRuntime(15058): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1053)
E/AndroidRuntime(15058): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1934)
在History.java行153是这样的：
The Line 153 in History.java is this:
ArrayList<Case> c = db.getAllContacts();
在历史课上，在分贝对象尚未宣布，因为从类该类inherites其中添加方法。
In the history class, the db object hasn't been declared its because this class inherites from the class where the add method is.
编辑3
我的历史课。
public class History extends SuperClass {
ListView lv;
ArrayList<Case> list;
ArrayList<Case> tempCaseList;
TextView header;
EditText ed;
String[] tempList;
int textLength;
TextView error;
Boolean[] isPresent;
DatabaseHandler db;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
super.setTabBar(R.layout.history);
lv = (ListView)findViewById(R.id.listOfCases);
list = new ArrayList<Case>();
list = getFromDatabase();
lv.setAdapter(new CustomAdapter(this, list));
lv.setTextFilterEnabled(true);
header = (TextView)findViewById(R.id.textView1);
header.setText("History");
error = (TextView)findViewById(R.id.error);
// db = new DatabaseHandler(this);
tempList = getCaseNumberToTempList(list);
tempCaseList = createTempList(list);
ed = (EditText)findViewById(R.id.editText1);
ed.addTextChangedListener(new TextWatcher() {
@Override
public void beforeTextChanged(CharSequence arg0, int arg1,
int arg2, int arg3) {
}
@Override
public void onTextChanged(CharSequence arg0, int arg1, int arg2,
int arg3) {
textLength = ed.getText().length();
list.clear();
isPresent = initIsPresentArray();
for (int i = 0; i < tempList.length; i++) {
for (int j = 0; j < (tempList[i].length()-(textLength-1)); j++) {
if (textLength <= tempList[i].length()) {
if(isPresent[i] == false){
if (ed.getText().toString().equalsIgnoreCase((String) tempList[i].subSequence(j,(j+textLength)))) {
list.add(tempCaseList.get(i));
isPresent[i] = true;
}
}
}
}
if(list.size() == 0) {
error.setText("Not Found");
}
else {
error.setText("");
}
lv.setAdapter(new CustomAdapter(History.this, list));
}
}
@Override
public void afterTextChanged(Editable arg0) {
// TODO Auto-generated method stub
}
});
}
public Boolean[] initIsPresentArray() {
Boolean[] isPresent = new Boolean[tempCaseList.size()];
for(int i = 0; i < isPresent.length; i++) {
isPresent[i] = false;
}
return isPresent;
}
public ArrayList<Case> createTempList(ArrayList<Case> listOfCases) {
ArrayList<Case> temporaryList = new ArrayList<Case>();
for(Case c : listOfCases) {
temporaryList.add(c);
}
return temporaryList;
}
public String[] getCaseNumberToTempList(ArrayList<Case> caseList) {
String[] objectCaseNumber = new String[caseList.size()];
for(int i = 0; i < caseList.size(); i++) {
objectCaseNumber[i] = caseList.get(i).getCaseNumber();
}
return objectCaseNumber;
}
public ArrayList<Case> getFromDatabase() {
ArrayList<Case> c = db.getAllContacts();
return c;
}
}
FINAL修改
发现我error..I只是忘了初始化。调用它使用该对象的方法之前，分贝对象。但我得到了另一个错误，这是不是这个线程的话题，所以我会发布一个新的线程，如果我再次获得卡住。谢谢。
Found my error..I just forgot the init. the db object before calling the method which uses this object. But I got another error, which is not the topic of this thread so I will post a new thread, if I get stuck again. Thanks.
推荐答案
按照你编辑的code在这里崩溃：
Following your edit, the code is crashing here:
ArrayList<Case> c = db.getAllContacts();
这里唯一的事情，可能会造成一个 NullPointerException异常是分贝本身就是空。您需要检查分贝已被正确地在这一点上开始工作。
The only thing here that could be causing a NullPointerException is db itself being null. You need to check that db has been correctly initialised at this point.
我刚才的答复，这仍然是有效的：
My earlier answer, which is still valid:
很难没有看到完整的stracktrace可以肯定的，但是这肯定看起来错了：
It's hard to be sure without seeing the full stracktrace, but this definitely looks wrong:
byte[] blob1 = cursor.getBlob(cursor.getColumnIndexOrThrow("2"));
这是寻找一个名为列2，它不存在。既然你已经知道你要找的BLOB的列索引，你可能是指这样的：
This is looking for a column named "2", which doesn't exist. Since you already know the column index of the blob you're looking for, you probably meant this:
byte[] blob1 = cursor.getBlob(2);
或另外，如果你真的想找到按列名索引：
or alternatively, if you really do want to find the index by column name:
byte[] blob1 = cursor.getBlob(cursor.getColumnIndexOrThrow("rightFinger"));
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