【发布时间】：2011-06-03 14:30:53
【问题描述】：
我对我的简单代码发生的事情感到困惑。即使我检查了代码流，它也不会进入另一个类文件。以下是我在android中的代码：
公共类 MedF1 扩展 ListActivity {
DrugsDbAdapter drugsDbAdapter = new DrugsDbAdapter(this);
DrugsDbAdapter.myDbHelper mDbHelper = new DrugsDbAdapter.myDbHelper(this);
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.drug_list);
try {
mDbHelper.createDataBase();
} catch (IOException ioe) {
throw new Error("Unable to create database");
}
try {
mDbHelper.openDataBase();
}catch(SQLException sqle){
throw sqle;
}
populateDrugList();
}
public void populateDrugList() {
Cursor drugListCursor = drugsDbAdapter.getAllEntries();
startManagingCursor (drugListCursor);
String[] from = new String[] {DrugsDbAdapter.KEY_DRUG};
int[] to = new int[] {R.id.text1};
SimpleCursorAdapter drugs = new SimpleCursorAdapter(this, R.layout.drug_row, drugListCursor, from, to);
setListAdapter(drugs);
}
数据库适配器类在下面，代码只是没有超出上面代码中populateDrugList()的druglistCursor！
public class DrugsDbAdapter {
private static final String DATABASE_TABLE = "data";
//The index column name for use in where clauses
public static final String KEY_ID = "_id";
//The name and column index of each column in DB
public static final String KEY_DRUG = "drug";
public static final String KEY_CONTENT = "content";
public static final String KEY_INDICATION = "indication";
public static final String KEY_DOSAGE = "dosage";
public static final String KEY_SPECIALPRECAUTION = "specialprecaution";
//variable to hold the database instance
private static SQLiteDatabase db;
//Context of the application using the database
private final Context context;
//Database open/upgrade helper
private myDbHelper dbHelper;
public DrugsDbAdapter(Context _context) {
this.context = _context;
}
public void open() throws SQLiteException {
try {
db = dbHelper.getWritableDatabase();
} catch (SQLiteException ex) {
db = dbHelper.getReadableDatabase();
}
}
//Creation of database and basic parameters
public static class myDbHelper extends SQLiteOpenHelper {
private static String DB_PATH = "data/data/com.paad.MedF1/databases/";
private static String DB_NAME = "data.sqlite";
private SQLiteDatabase myDataBase;
private Context myContext;
public myDbHelper (Context context) {
super(context, DB_NAME, null, 1);
this.myContext = context;
}
public void createDataBase() throws IOException{
boolean dbExist = checkDataBase();
if(dbExist) {
// do nothing
} else {
this.getReadableDatabase();
try {
copyDataBase();
} catch (IOException e) {
throw new Error ("Error copying database");
}
}
}
private boolean checkDataBase(){
boolean checkDB = false;
try{
String myPath = DB_PATH + DB_NAME;
File dbfile = new File(myPath);
checkDB = dbfile.exists();
}catch(SQLiteException e){
//database does't exist yet.
}
return checkDB;
}
private void copyDataBase() throws IOException{
//Open your local db as the input stream
InputStream myInput = myContext.getAssets().open(DB_NAME);
// Path to the just created empty db
String outFileName = DB_PATH + DB_NAME;
//Open the empty db as the output stream
OutputStream myOutput = new FileOutputStream(outFileName);
//transfer bytes from the inputfile to the outputfile
byte[] buffer = new byte[1024];
int length;
while ((length = myInput.read(buffer))>0){
myOutput.write(buffer, 0, length);
}
//Close the streams
myOutput.flush();
myOutput.close();
myInput.close();
}
public void openDataBase() throws SQLException{
//Open the database
String myPath = DB_PATH + DB_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) {
}
}
public void close() {
db.close();
}
public long insertEntry(myDrug _myDrug) {
ContentValues newDrugValues = new ContentValues();
newDrugValues.put(KEY_DRUG, _myDrug.getDrug());
newDrugValues.put(KEY_CONTENT, _myDrug.getContent());
newDrugValues.put(KEY_INDICATION, _myDrug.getIndication());
newDrugValues.put(KEY_DOSAGE, _myDrug.getDosage());
newDrugValues.put(KEY_SPECIALPRECAUTION, _myDrug.getSpecialprecaution());
return db.insert(DATABASE_TABLE, null, newDrugValues);
}
public boolean removeEntry (long _rowIndex) {
return db.delete(DATABASE_TABLE, KEY_ID + "=" + _rowIndex, null) > 0;
}
public Cursor getAllEntries () {
return db.query(DATABASE_TABLE, new String[] {KEY_ID, KEY_DRUG, KEY_CONTENT, KEY_INDICATION, KEY_DOSAGE, KEY_SPECIALPRECAUTION}, null, null, null, null, null);
}
}
救命！！！我的 logcat 输出是：
06-03 22:29:01.636: ERROR/AndroidRuntime(1424): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.paad.MedF1/com.paad.MedF1.MedF1}: java.lang.NullPointerException
06-03 22:29:01.636: ERROR/AndroidRuntime(1424): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
06-03 22:29:01.636: ERROR/AndroidRuntime(1424): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
06-03 22:29:01.636: ERROR/AndroidRuntime(1424): at android.app.ActivityThread.access$2300(ActivityThread.java:125)
06-03 22:29:01.636: ERROR/AndroidRuntime(1424): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
06-03 22:29:01.636: ERROR/AndroidRuntime(1424): at android.os.Handler.dispatchMessage(Handler.java:99)
06-03 22:29:01.636: ERROR/AndroidRuntime(1424): at android.os.Looper.loop(Looper.java:123)
06-03 22:29:01.636: ERROR/AndroidRuntime(1424): at android.app.ActivityThread.main(ActivityThread.java:4627)
06-03 22:29:01.636: ERROR/AndroidRuntime(1424): at java.lang.reflect.Method.invokeNative(Native Method)
06-03 22:29:01.636: ERROR/AndroidRuntime(1424): at java.lang.reflect.Method.invoke(Method.java:521)
06-03 22:29:01.636: ERROR/AndroidRuntime(1424): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
06-03 22:29:01.636: ERROR/AndroidRuntime(1424): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
06-03 22:29:01.636: ERROR/AndroidRuntime(1424): at dalvik.system.NativeStart.main(Native Method)
06-03 22:29:01.636: ERROR/AndroidRuntime(1424): Caused by: java.lang.NullPointerException
06-03 22:29:01.636: ERROR/AndroidRuntime(1424): at com.paad.MedF1.MedF1.populateDrugList(MedF1.java:51)
06-03 22:29:01.636: ERROR/AndroidRuntime(1424): at com.paad.MedF1.MedF1.onCreate(MedF1.java:45)
06-03 22:29:01.636: ERROR/AndroidRuntime(1424): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
06-03 22:29:01.636: ERROR/AndroidRuntime(1424): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
06-03 22:29:01.636: ERROR/AndroidRuntime(1424): ... 11 more
【问题讨论】：
-
您是否将活动包含在清单中？
-
MedF1.java 中第 45 行和第 51 行之间的内容
标签： android class nullpointerexception