Develop Reference

LinkedHashSet does not main insertion order?

I am currently building an Android app where I display quotes from famous people. I have a home screen and 2 other screens, where I am displaying all quotes and the other where I display favourite quotes.
So, when I hit the like button in the screen of AllQuotesActivity the quote and author will be saved in a LinkedHashSet, which will be saved in SharedPreferences, so my FavouriteQuotes Activity can obtain the data. I can obtain the data, but the data is mixed, even though other links say that LinkedHashSet maintains the insertion order. Maybe I did something wrong. Here are the important code snippets:
AllQuotesActivity.java:
SharedPreferences sharedPref;
Set<String> set = new LinkedHashSet();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.all_quotes);
Resources res = getResources();
Context context = getApplicationContext();
this.sharedPref = context.getSharedPreferences(
"MyPref", Context.MODE_PRIVATE);
final String[] quotesAndAuthors = res.getStringArray(R.array.quotes);
button3.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
set.add(quotesAndAuthors[counter]);
set.add(quotesAndAuthors[counter + 1]);
}
});
}
#Override
public void onPause() {
super.onPause();
Log.d("RichQuotes", "Its paused mkay");
Editor editor = sharedPref.edit();
editor.putStringSet("quotesAndAuthors", this.set);
editor.commit();
}
}
FavouriteQuotesActivity.java:
SharedPreferences sharedPref;
Set<String> set = new LinkedHashSet();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.favourite_quotes);
Resources res = getResources();
Context context = getApplicationContext();
this.sharedPref = context.getSharedPreferences(
"MyPref", Context.MODE_PRIVATE);
set = sharedPref.getStringSet("quotesAndAuthors", null);
for (Iterator<String> it = set.iterator(); it.hasNext(); ) {
String s = it.next();
Log.v("test", s);
}
I removed unnecessary code.
In the FavouriteQuotesActivity.java I am logging the set to check its values. The log-outputs and the outputs on the screen are the same, both unsorted the same way.

Set set = new LinkedHashSet();
In this line, you instantiate a new empty LinkedHashSet object. This object was then assigned to the variable named set.
set = sharedPref.getStringSet("quotesAndAuthors", null);
In this line, you reassigned the set variable to point to some other object, some Set object returned by your call to getStringSet. We do not know the concrete class of this second object that implements the Set interface. You can ask by calling getClass.
Your first set, the empty LinkedHashSet, went unused. With no other references pointing to it, that set became a candidate for eventual garbage-collection.

I cant delete some rows by id in SQLite

I always cant delete first two sometimes three records. They are on Listview, when you press element you will see delete button on another layout. On Log im getting correct index for every element.
So here is my code:
Main Activity:
viewOfT.setOnItemClickListener(new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
Intent i=new Intent(MainActivity.this, popupWindow.class);
i.putExtra("index",id);
startActivity(i);
}
});
}
public void populateListView() {
Cursor data = db.getData();
ArrayList<String> listData = new ArrayList<>();
while(data.moveToNext()){
k.setId(data.getInt(0));
k.setTask(data.getString(1));
listData.add("- " + k.getTask());
}
ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(
this,
android.R.layout.simple_list_item_1,
listData);
viewOfT.setAdapter(arrayAdapter);
arrayAdapter.notifyDataSetChanged();
viewOfT.invalidateViews();
Delete button in other activity:
del.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View v) {
Bundle bundle=getIntent().getExtras();
long value=bundle.getLong("index");
db.deleteRecord(value);
finish(); }
});
And SQLHelper:
public void deleteRecord(long id) {
SQLiteDatabase db = this.getWritableDatabase();
db.delete(TABLE_NAME, KEY_ID + "=" + id, null);
close();
}

1) Delete populateListView method
2) Add the following as class variables:-
SimpleCursorAdpater sca;
Cursor data;
3) in the onCreate method add :-
data = getData();
sca = new SimpleCursorAdapter(
this, // Context same as for array adapter
android.R.layout.simple_list_item_1, // layout to be used
data, // <<<<<<<< the cursor to be used for the list
new String[]{"columnname_to_be_displayed"}, // <<<<<<<< cursor column to display name
new int[android.R.id.text1], // the view into which the cursor data will be placed
0 // a flag 0 is fine
);
viewOfT.setAdapter(arrayAdapter);
4) Add a new method to override the 'onResume' method (or alter it if already overridden) :-
#Override
protected void onResume() {
super.onResume();
data = getData();
sca.swapCursor(); // can you sca.notifyDatasetChanged()
}
As you are calling another activity to delete the task, onResume will be called when returning from the other activity so the data is again retrieved from the database (deleted row will not exist) and the adpater is told to refresh the data.
You should ideally also override the onDestroy() method to close the cursor (data.close();)
Important Consideration
A cursor column named _id must exist for CursorAdapters (that's how the SimpleCursorAdapter knows what pass to the onItemClickListener).
if KEY_ID does not equate to _id; you either need to change KEY_ID to _id or amend the getData() method to include the _id column (which should be the value of the row's identifier) e.g. assuming a very basic query:
public Cursor getData() {
return db.query(TABLE_NAME,"rowid AS _id, *",null,null,null,null,null);
} // Note! will add an extra column so beware if using column offsets
or perhaps :-
public Cursor getData() {
return db.query(TABLE_NAME,KEY_ID + " AS _id, *",null,null,null,null,null);
} // Note! will add an extra column so beware if using column offsets
A Note on Column offsets
In your code you have :-
k.setId(data.getInt(0));
k.setTask(data.getString(1));
0 and 1 are column offsets (and could change e.g. the two alternative getData() methods). As such it's generally better to take advantage of the Cursor method getColumnIndex(columnname) e.g. the above could be :-
k.setId(data.getInt(data.getColumnIndex(KEY_ID));
k.setTask(data.getString(data.getColumnIndex("TASK_COLUMN")));
Note! not that you will need to create an Array as the SimpleCursorAdpater takes the cursor as the source. (KEY_ID would likely have to be prefixed with the DatabaseHelper Class).

Keeping list entries when I move activity

I have a ListView.
I populate this list from 2 editTexts
When I move activity and go back to it the entries are gone again.
I kind of understand why this is but dont know how to correct it.
ListView lv2 = (ListView) findViewById(R.id.listView2);
final SimpleAdapter simpleAdpt = new SimpleAdapter(this, planetsList, android.R.layout.simple_list_item_1, new String[]{"planet"}, new int[]{android.R.id.text1});
planetsList.add(createPlanet("planet", "testme"));
lv2.setAdapter(simpleAdpt);
button21.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
iinitList();
simpleAdpt.notifyDataSetChanged();
editText5.setText("");
editText6.setText("");
}
});
}
private void iinitList() {
String st,str;
Double db;
if (editText5.getText().toString()!= "" && editText6.getText().toString()!="") {
st = editText5.getText().toString();
str = editText6.getText().toString();
db = Double.parseDouble(str);
planetsList.add(createPlanet("planet", ""+st+
": \n" +db+""));
}
}
HashMap<String, String> createPlanet(String key, String name) {
HashMap<String, String> planet = new HashMap<String, String>();
planet.put(key, name);
return planet;
}
As you can see I have added a value to the list manually called test also, when I move activity this stays in the list, I would love if the editText entries were to stay in there also when I move activities.

Activities can be destroyed when you navigate to a new one or rotate. This will clear anything that is only referenced by the activity, like your EditTexts. However, Android provides a nice utility for saving things you want to remain in a method called, which you can override in your activity:
#Override
protected void onSaveInstanceState(Bundle state) {
// Put your values in the state bundle here
}
#Override
protected void onCreate(Bundle savedState) {
// Load your UI elements as usual
if (savedState != null) {
// Load your state from the bundle
}
}
That same bundle will be given back to you in onCreate, where you create your UI to begin with so you can reload the state from it.
This is a really good description of how activities work:
http://developer.android.com/reference/android/app/Activity.html

Android ListView: How to add a row with a buttonclick

I have a listview. In it, each row had a text saying 0:00. But now, I added a button on my actionbar but then I got stuck. I don't know how to make the button create a new row, displaying 0:00
This is my code for the data in a row.
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
RowData rowdata_data[] = new RowData[]
{
new RowData("0:00")
};
RowdataAdapter adapter = new RowdataAdapter(this,
R.layout.listview_item_row, rowdata_data);
listView1.setAdapter(adapter);
listView1 = (ListView)findViewById(R.id.listView1);
}
this is my RowData class:
public class RowData {
String title;
public RowData(String title) {
this.title = title;
}
}
So how should I implement a button click to add another row?
Under addtionbutton: should be the method.
public boolean onOptionsItemSelected(MenuItem item)
{
// Handle presses on the action bar items
switch (item.getItemId())
{
case R.id.additionbutton:
return true;
default:
return super.onOptionsItemSelected(item);
}
}

I don't know how to make the button create a new row
With your current solution it's not possible (in efficient way do it) because you're using static array of objects - it means array has fixed size (it means that you're assuming that size won't be changed at runtime).
But your goal is "slightly" different. You want after each click on Button increase number of objects by one. It means you don't know exactly how many rows you can have (or can be changed at runtime).
Due to things mentioned above you should (have to) use dynamic array with changeable size. For this reason you need to use as source of data List that is representation of dynamic array.
Basic algorithm:
Create new List with zero (or you can have by default one row at
start).
Then create public method in your adapter that will add new item to
collection and send request that Adapter should be refreshed (after you added new row into collection).
Assign OnClickListener to your Button and in onClick() method you'll use created method for adding new row into ListView.
Solution:
How to initialise ListAdapter:
// Activity-level variable scope
private List<RowData> items = new ArrayList<RowData>();
private RowdataAdapter adapter;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
listView1 = (ListView)findViewById(R.id.listView1);
// adding first item to List, it's optional step
items.add(new RowData("0:00"));
adapter = new RowdataAdapter(this, R.layout.listview_item_row, items);
listView1.setAdapter(adapter);
}
Method for adding new row into ListAdapter:
public void addRow(RowData newRow) {
// items represents List<RowData> in your Adapter class
this.items.add(newRow);
// sends request to update ListAdapter
notifyDataSetChanged();
}
How to update Adapter after click on Button:
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// add new row to Adapter
adapter.addRow(new RowData("0:00"));
}
});
Hope i helped you to solve your problem.

you need to create a dataset that you can change so you need to make your array a class wide variable so you can add to it when you need to
when you add the new row you need to notify the adapter that something changed so you do this
adapter.notifyDatasetChanged();
and that should update your list

android - SimpleCursorAdapter for a View

is it possible to create a View which is driven by a SimpleCursorAdapter. The content from this view is ever time a entry from DB.
The View (dataView) looks like:
txtData1
txtData2
txtData3
btnPrev btnNext
I read around and tryd to setup this behavior. Hope its make sens:
public class mActivity extends Activity {
public Context me = this;
public SimpleCursorAdapter mAdapter = null;
public Cursor mCursor = null;
private OnClickListener btnStart_onClick = new OnClickListener() {
public void onClick(View v) {
setContentView(R.layout.dataView);
mCursor = mDB.rawQuery("SELECT * FROM Data", null);
startManagingCursor(mCursor);
mAdapter = new SimpleCursorAdapter(
me,
R.layout.dataView,
mCursor,
new String[] {"Data1", "Data2", "Data3"},
new int[] {R.id.txtData1 , R.id.txtData2, R.id.txtData3});
mAdapter.setViewBinder(VIEW_BINDER);
mCursor.moveToFirst();
}
};
static final ViewBinder VIEW_BINDER = new ViewBinder() {
public boolean setViewValue(View view, Cursor cursor, int columnIndex)
{
switch (view.getId())
{
case R.id.txtData1:
TextView txt = (TextView) view;
if (txt != null)
{
int index = cursor.getColumnIndex("Data1");
txt.setText(cursor.getString(index));
}
return true;
case R.id.txtData2:
TextView txt = (TextView) view;
if (txt != null)
{
int index = cursor.getColumnIndex("Data2");
txt.setText(cursor.getString(index));
}
return true;
case R.id.txtData3:
TextView txt = (TextView) view;
if (txt != null)
{
int index = cursor.getColumnIndex("Data3");
txt.setText(cursor.getString(index));
}
return true;
default:
return false;
}
}
};
}
When I run from the btnStart_onClick I dont get Data in my Textboxes :-(
Can somebody help? Can it work like this?
Next question: how can I use the Prev or Next Buttons? Possible this is the only thing I miss to "load" the first data...
EDIT: I extended my example with the global mCursor and the call to mCursor.moveToFirst()
On my app I also tested with the next / prev buttons and the function mCursor.moveToNext() and mCursor.moveToPrevious()
But its not change :-(

As far as I can tell, there are a lot of what I think are conceptual/organizational/syntactical problems with your code. First of all, an adapter is usually exploited by a view such as ListView or Spinner, that gets populated with the data retrieved by the adapter via the cursor (or whatever data structure is backing it). However, I don't see this pattern in your code, and I'm left wondering what use an adapter would have in your case.
Second, you perform a whole SELECT * query in your click listener, i.e. you retrieve all your 1000 records for each click on... well, on what, exactly? You define the click listener, but never set it onto anything - just as you define the adapter, but you don't bind it to anything. The code that sets up the adapter, with the database query and the binder should really be placed outside the listener.
Last, I believe you mocked variable names a bit before posting the code, because in the following snippet:
TextView txt = (TextView) view;
if (txt != null)
{
int index = cursor.getColumnIndex("Data1");
String txt = cursor.getString(index);
txt.setText(txt);
}
I could hardly see how the compiler is intended to distinguish the two txt variables on the last line of the if body.