我正在构建一个在ListFragment中显示项目的应用程序。现在每个项目都显示标题和创建日期。还有另外两个片段。一个创建项目并具有EditText字段，我可以编辑标题。另一个只是显示单个项目的内容。
我遇到的问题是，每次我在EditText字段中输入一个字符，应用程序就会关闭。错误消息表明错误发生在TextChangedListener中的onTextChanged上。因为当我将所有内容存储为JSON文件时，我将此功能工作，所以必须发生错误，因为我更新数据库和更新模型层的方式。
此文件执行所有数据库操作并创建自定义Cursor。
public class SnapDatabaseHelper extends SQLiteOpenHelper {
private static final String TAG = "FeedFragment";
private static final String DB_NAME = "snap.sqlite";
private static final int VERSION = 1;
private static final String TABLE_SNAP = "snap";
private static final String COLUMN_SNAP_ID = "_id";
private static final String COLUMN_SNAP_DATE = "snap_date";
private static final String COLUMN_SNAP_UUID = "snap_uuid";
private static final String COLUMN_SNAP_TITLE = "snap_title";
public SnapDatabaseHelper(Context context){
super(context, DB_NAME, null, VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
// Create SNAP table
db.execSQL("create table snap(" +
"_id integer primary key autoincrement, " +
//"snap_uuid text, " +
"snap_date integer, " +
"snap_title text) ");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
//
}
public long insertSnap(Snap snap){
ContentValues cv = new ContentValues();
//cv.put(COLUMN_SNAP_UUID, snap.getUniqueId().toString());
cv.put(COLUMN_SNAP_DATE, snap.getDate().getTime());
cv.put(COLUMN_SNAP_TITLE, "");
return getWritableDatabase().insert(TABLE_SNAP, null, cv);
}
public boolean updateTitle(long snapId, String text)
{
ContentValues cv = new ContentValues();
cv.put(COLUMN_SNAP_ID, snapId);
cv.put(COLUMN_SNAP_TITLE, text);
int i= getWritableDatabase().update(TABLE_SNAP, cv, COLUMN_SNAP_ID+ "=" + snapId, null);
return i>0;
}
public SnapCursor querySnap(long id) {
Cursor wrapped = getReadableDatabase().query(TABLE_SNAP,
null, // all columns
COLUMN_SNAP_ID + " = ?", // look for a run ID
new String[]{ String.valueOf(id) }, // with this value
null, // group by
null, // order by
null, // having
"1"); // limit 1 row
return new SnapCursor(wrapped);
}
public SnapCursor querySnaps() {
// equivalent to "select * from run order by start_date asc"
Cursor wrapped = getReadableDatabase().query(TABLE_SNAP,
null, null, null, null, null, COLUMN_SNAP_DATE + " asc");
return new SnapCursor(wrapped);
}
public static class SnapCursor extends CursorWrapper{
public SnapCursor(Cursor c){
super(c);
}
public Snap getSnap() {
if (isBeforeFirst() || isAfterLast())
return null;
Snap s = new Snap();
s.setId(getLong(getColumnIndex(COLUMN_SNAP_ID)));
//s.setUniqueId(UUID(getString(getColumnIndex(COLUMN_SNAP_UUID))));
s.setDate(new Date(getLong(getColumnIndex(COLUMN_SNAP_DATE))));
s.setTitle(getString(getColumnIndex(COLUMN_SNAP_TITLE)));
return s;
}
}
}
此文件将片段链接到DatabaseHelper。
public class SnapLab {
private static SnapLab sSnapLab;
private Context mAppContext;
private SnapDatabaseHelper mHelper;
// private constructor
private SnapLab(Context appContext){
mAppContext = appContext;
mHelper = new SnapDatabaseHelper(mAppContext);
}
public static SnapLab get(Context c){
if(sSnapLab == null){
sSnapLab = new SnapLab(c.getApplicationContext());
}
return sSnapLab;
}
public Snap insertSnap() {
Snap s = new Snap();
s.setId(mHelper.insertSnap(s));
return s;
}
public boolean updateTitle(long snapId, String text){
return mHelper.updateTitle(snapId, text);
}
public SnapCursor querySnaps() {
return mHelper.querySnaps();
}
public Snap getSnap(long id) {
Snap s = null;
SnapCursor cursor = mHelper.querySnap(id);
cursor.moveToFirst();
// if we got a row, get a run
if (!cursor.isAfterLast())
s = cursor.getSnap();
cursor.close();
return s;
}
}
这是带有EditText字段的片段
public class EditPageFragment extends Fragment {
private static final String TAG = "EditPageFragment";
public static final String EXTRA_SNAP_ID = "SNAP_ID";
private SnapLab mSnapLab;
private Snap mSnap;
private SnapDatabaseHelper mHelper;
private EditText mSnapText;
private Button mUploadButton;
private TextView mDateText;
private Long snapId;
public static EditPageFragment newInstance(Long snapId){
Bundle args = new Bundle();
args.putLong(EXTRA_SNAP_ID, snapId);
EditPageFragment fragment = new EditPageFragment();
fragment.setArguments(args);
return fragment;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setRetainInstance(true);
mSnapLab = SnapLab.get(getActivity());
Bundle args = getArguments();
if (args != null){
long snapId = args.getLong(EXTRA_SNAP_ID, -1);
if (snapId != -1){
mSnap = mSnapLab.getSnap(snapId);
}
}
mSnap = new Snap();
mSnap = mSnapLab.insertSnap();
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup parent, Bundle savedInstanceState){
View v = inflater.inflate(R.layout.edit_fragment, parent, false);
mDateText = (TextView)v.findViewById(R.id.edit_dateText);
mDateText.setText(mSnap.getDate().toString());
mSnapText = (EditText)v.findViewById(R.id.edit_snapText);
mSnapText.addTextChangedListener(new TextWatcher(){
@Override
public void afterTextChanged(Editable s) {
//leave blank for now
}
@Override
public void beforeTextChanged(CharSequence c, int start, int count,
int after) {
//leave blank for now
}
@Override
public void onTextChanged(CharSequence c, int start, int before,
int count) {
mSnap.setTitle(c.toString());
mSnapLab.updateTitle(snapId, c.toString());
Log.i(TAG, "text saved");
}
});
return v;
}
}
代码的导入位是updateTitle（）函数。我能做错什么？您对如何更好地更新数据库有一个建议吗？除了更新标题外，一切都很有效。我很感激你的帮助。
答案 0 :(得分：0)
看起来没有分配snapId
private Long snapId; //field
以后几行
long snapId = args.getLong(EXTRA_SNAP_ID, -1); //local variable
以后几行
mSnapLab.updateTitle(snapId, c.toString()); //field
请在下次添加stacktrace。