我在删除数据库中的标记时遇到了很多麻烦，特别是标记表。目前，我正在创建一个新的MapsMarker（下面看到的对象）并通过将其插入到我的表中来获得长结果，然后使用此结果来获取要删除的ID。但这不起作用，因为使用.insert方法会为我的数据库添加额外的标记。所以我的问题是，如果没有（或使用任何一种方式）使用.insert，我怎样才能正确地从数据库中删除标记，因为这会为我的数据库添加一个新标记。
Here is my AddMarker method:
/**
* Method for adding a marker to the database and returning its ID if needed (for deletion, find, etc.)
* @param marker
* @return
*/
public long addMapsMarker(MapsMarker marker) {
ContentValues values = new ContentValues(); //Dont .put COLUMN_MARKER_ID because it is autoincrementing
values.put(DBQueryModelHelper.COLUMN_LAT, marker.getLat());
values.put(DBQueryModelHelper.COLUMN_LONGITUDE, marker.getLong());
long result = SQDatabase.insert(DBQueryModelHelper.TABLE_LOCATION, null, values);
//marker.setId(result);
marker.setId(result - 1); //sets the added marker ID to the row ID where it was inserted (same value as the autoincrementing ID)
long bb = marker.getId();
return result;
}
My delete method:
/**
* Method for deleting a marker, currently deletes from database but marker is reloaded.
* @param marker
*/
public void deleteMapsMarker(MapsMarker marker){
long id = marker.getId();
SQDatabase.delete(DBQueryModelHelper.TABLE_LOCATION, DBQueryModelHelper.COLUMN_MARKER_ID + "=?",
new String[]{Long.toString(id)});
}
我的MapsMarker对象是一个包含纬度和经度的对象，但也有一个私有ID以及这些字段的所有getter和setter。
这是我正在尝试删除的Map Activity：
public void setUsermarker() {
mMap.setOnMarkerClickListener(new OnMarkerClickListener() {
@Override
public boolean onMarkerClick(final Marker marker) {
new AlertDialog.Builder(MapsActivity.this)
.setMessage("View imagery or delete this marker?")
//Delete user marker
.setPositiveButton("Delete Marker", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
marker.remove();
MapsMarker markerforDelete = new MapsMarker(marker.getPosition().latitude, marker.getPosition().longitude);
long tablerowid = MarkerHelper.addMapsMarker(markerforDelete);
markerforDelete.setId(tablerowid);
MarkerHelper.deleteMapsMarker(markerforDelete);
}
})
.setNegativeButton("View 3D", new DialogInterface.OnClickListener() {
// Start 3D view activity
public void onClick(DialogInterface dialog, int which) {
Intent intent = new Intent(MapsActivity.this, BuildingViewActivity.class);
startActivity(intent);
}
})
.setIcon(android.R.drawable.ic_dialog_alert)
.show();
return true;
}
});
}
答案 0 :(得分：0)
我想说，更好的方法是编写模块化代码而不是将所有代码放在一起。当您希望在调用回调后经常执行插入/删除选项时，使用内容提供程序是一个更好的主意。
创建一个类，该类将在DB类顶部的Content Providers的帮助下将位置存储在DB中，这将简化整个过程。
/** A custom Content Provider to do the database operations */
public class LocationsContentProvider extends ContentProvider{
public static final String PROVIDER_NAME = "com.mapv2.demo.locations";
/** A uri to do operations on locations table. A content provider is identified by its uri */
public static final Uri CONTENT_URI = Uri.parse("content://" + PROVIDER_NAME + "/locations" );
/** Constant to identify the requested operation */
private static final int LOCATIONS = 1;
private static final UriMatcher uriMatcher ;
static {
uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
uriMatcher.addURI(PROVIDER_NAME, "locations", LOCATIONS);
}
/** This content provider does the database operations by this object */
LocationsDB mLocationsDB;
/** A callback method which is invoked when the content provider is starting up */
@Override
public boolean onCreate() {
mLocationsDB = new LocationsDB(getContext());
return true;
}
/** A callback method which is invoked when insert operation is requested on this content provider */
@Override
public Uri insert(Uri uri, ContentValues values) {
long rowID = mLocationsDB.insert(values);
Uri _uri=null;
if(rowID>0){
_uri = ContentUris.withAppendedId(CONTENT_URI, rowID);
}else {
try {
throw new SQLException("Failed to insert : " + uri);
} catch (SQLException e) {
e.printStackTrace();
}
}
return _uri;
}
@Override
public int update(Uri uri, ContentValues values, String selection,
String[] selectionArgs) {
// TODO Auto-generated method stub
return 0;
}
/** A callback method which is invoked when delete operation is requested on this content provider */
@Override
public int delete(Uri uri, String selection, String[] selectionArgs) {
int cnt = 0;
cnt = mLocationsDB.del();
return cnt;
}
/** A callback method which is invoked by default content uri */
@Override
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
if(uriMatcher.match(uri)==LOCATIONS){
return mLocationsDB.getAllLocations();
}
return null;
}
@Override
public String getType(Uri uri) {
return null;
}
}
从前端，您可以使用单独的线程查询数据库以获取内容解析器，然后插入或删除。
private class LocationInsertTask extends AsyncTask<ContentValues, Void, Void>{
@Override
protected Void doInBackground(ContentValues... contentValues) {
/** Setting up values to insert the clicked location into SQLite database */
getContentResolver().insert(LocationsContentProvider.CONTENT_URI, contentValues[0]);
return null;
}
}
private class LocationDeleteTask extends AsyncTask<Void, Void, Void>{
@Override
protected Void doInBackground(Void... params) {
/** Deleting all the locations stored in SQLite database */
getContentResolver().delete(LocationsContentProvider.CONTENT_URI, null, null);
return null;
}
}
有关其他信息，您可以查看此tutorial。