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我希望我的問題不是太寬泛。我真正想知道的是如何準確地確定我的代碼在牆上的位置。Android Studio應用程序崩潰從Sqlite數據庫
我沒有從調試器收到錯誤，應用程序在模擬器啓動使用sqlite數據庫的活動（第3個活動）時崩潰。我很積極，它是我的代碼中添加了sqlite，導致崩潰，因爲它在我添加之前運行。
此代碼只需訪問並從我創建並粘貼到資產文件夾的外部數據庫中讀取。我回顧了firefox的SQLite管理器中的sqlite數據庫;該信息似乎被正確格式化。
我在app/src/Main中創建了資產文件夾，以方便添加外部數據庫「ex3.db」。然後我在那裏複製並粘貼數據庫文件。
所以這裏是代碼。 LetterImage是一個保存從sqlite數據庫檢索的字符串的類。 MyDBHandler創建一個空數據庫，將舊數據庫複製到其中，並使用基於字符串的查詢返回的值填充LetterImage。 LoadSubjectActivity調用它們來搜索數據庫並返回一個字符串。
LetterImage：
public class LetterImage {
private Integer _ID;
private String _letter;
private String _bigfilename;
private String _littlefilename;
//Constructor(s)
public LetterImage(){
}
public LetterImage(Integer ID, String letter, String bigfilename, String littlefilename){
this._ID = ID;
this._letter = letter;
this._bigfilename = bigfilename;
this._littlefilename = littlefilename;
}
public LetterImage(String letter){
this._letter = letter;
}
//End Constructors
//Begin setters and getters
//ID is primary key
public void setID(Integer ID){
this._ID = ID;
}
public Integer getID(){
return this._ID;
}
//letter is main identifier used to search database
// passed to LoadSubjectActivity
// from ChooseSubjectABCActivity as extra from intent
public void setLetter(String letter){
this._letter = letter;
}
public String getLetter(){
return this._letter;
}
//Capital letter image file name
public void setBigFileName(String bigfilename){
this._bigfilename = bigfilename;
}
public String getBigFileName(){
return this._bigfilename;
}
//Lowercase Letter image file name
public void setLittleFileName(String littlefilename){
this._littlefilename = littlefilename;
}
public String getLittleFileName(){
return this._littlefilename;
}
}
現在，這裏是MyDBHandler：
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.content.Context;
import android.database.Cursor;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.sql.SQLException;
public class MyDBHandler extends SQLiteOpenHelper{
private final Context myContext;
private static Context context;
private static final int DATABASE_VERSION = 1;
private static String DB_PATH = "data/data" + context.getPackageName() + "/databases/";
private static final String DATABASE_NAME = "ex3.db";
public static final String TABLE_IMAGES = "tbl1";
private SQLiteDatabase myDataBase;
//Fields in Database
public static final String COLUMN_ID = "_id";
public static final String COLUMN_BIGIMAGEFILE = "bigImage";
public static final String COLUMN_LITTLEIMAGEFILE = "littleImage";
public static final String COLUMN_LETTER = "letter";
//Constructor
public MyDBHandler(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
this.myContext = context;
}
//if there is no existing database, create an empty one
public void createDatabase() throws IOException{
boolean dbExist = checkDataBase();
if(dbExist) {
//do nothing
}else {
//call this method and create an empty database
this.getReadableDatabase();
try {
copyDataBase();
} catch(IOException e){
throw new Error("Error copying database");
}
}
}
//check to see if there is an existing database
private boolean checkDataBase(){
SQLiteDatabase checkDB = null;
try{
String myPath = DB_PATH + DATABASE_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
} catch (SQLiteException e){
throw new Error("Unable to open database");
}
if(checkDB != null){
checkDB.close();
}
return checkDB != null ? true : false;
}
//fills new empty database with existing database ex3
private void copyDataBase() throws IOException{
InputStream myInput = myContext.getAssets().open(DATABASE_NAME);
String outFileName = DB_PATH + DATABASE_NAME;
OutputStream myOutput = new FileOutputStream(outFileName);
byte[] buffer = new byte[1024];
int length;
while ((length = myInput.read(buffer))>0){
myOutput.write(buffer, 0, length);
}
myOutput.flush();
myOutput.close();
myInput.close();
}
//opens the new database
public void openDatabase() throws SQLException {
String myPath = DB_PATH + DATABASE_NAME;
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}
@Override
public synchronized void close(){
if(myDataBase != null)
myDataBase.close();
super.close();
}
@Override
public void onCreate(SQLiteDatabase db){
}
@Override
public void onUpgrade(SQLiteDatabase db, int OldVersion, int newVersion){
}
//creates an instance of letter LetterImage
//queries the new database by searching for the row with where the value of COLUMN_LETTER = letter
//fills LetterImage with the values from that row
public LetterImage findLetter(String letter) {
String query = "Select * FROM " + TABLE_IMAGES + " WHERE " + COLUMN_LETTER + " = \"" + letter + "\"";
SQLiteDatabase db = this.getWritableDatabase();
Cursor cursor = db.rawQuery(query, null);
LetterImage LetterImage = new LetterImage();
if (cursor.moveToFirst()) {
cursor.moveToFirst();
LetterImage.setID(Integer.parseInt(cursor.getString(0)));
LetterImage.setBigFileName(cursor.getString(1));
LetterImage.setLittleFileName(cursor.getString(2));
LetterImage.setLetter(cursor.getString(3));
cursor.close();
} else {
LetterImage = null;
}
db.close();
return LetterImage;
}
}
最後，這裏有LoadSubjectActivity類的相關部分：
public class LoadSubjectActivity extends MainActivity{
private DrawingView drawView;
private ImageButton currPaint;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.content_load_subject);
//receives string letter, from last activity
//letter will be used to search array and return files names of the images to be used
Intent intent = getIntent();
String letter = intent.getExtras().getString("letter");
//displayFN calls testDB(letter) to test the database
//It should simply display the string returned by testDB()
TextView displayFN = (TextView)findViewById(R.id.display_filenames);
displayFN.setText(testDB(letter.toLowerCase()));
//Eventually, button images will be filled dynamically
ImageButton bigLetter = (ImageButton)findViewById(R.id.big_letter);
ImageButton littleLetter = (ImageButton)findViewById(R.id.little_letter);
bigLetter.setImageResource(R.drawable.biga);
littleLetter.setImageResource(R.drawable.littlea);
drawView = (DrawingView)findViewById(R.id.drawing);
LinearLayout paintLayout = (LinearLayout)findViewById(R.id.paint_colors);
currPaint = (ImageButton)paintLayout.getChildAt(0);
currPaint.setImageDrawable(ContextCompat.getDrawable(this, R.drawable.paint_pressed));
}
//Function to test the database takes a string as an argument to search the database
public String testDB(String letter){
//create a new instance of dbHandler
MyDBHandler dbHandler = new MyDBHandler(this);
//try to either create an empty database or open the existing one
try{
dbHandler.createDatabase();
} catch (IOException ioe){
throw new Error("Unable to create database");
}
try{
dbHandler.openDatabase();
} catch(SQLException sqle){
sqle.printStackTrace();
throw new Error ("unable to open database");
}
LetterImage letterImage = dbHandler.findLetter(letter);
String blFileName = letterImage.getBigFileName();
//return the big letter image file name;
return blFileName;
}
反正我在道歉提前解決任何明顯的問題。我已經盡我所能地追溯了邏輯......我自學java和sql ...這是我的第一個android項目。任何和所有的見解，非常感謝。
如果您有答案，請填寫答案。 –