Develop Reference

Recycler View Onclick method in Activity?

I'm trying to create a UI similar to Google Keep. I know how to create a staggered View using a Recycler View. If i click a specific Card. Then it has to open a activity.
I can achieve this using onclick method.
This same scenario happens in atleast 5 different Activities in my App.
My question is that
Can I use this single Adapter in all those 5 places ?
If yes, where should i place the onclick actions ?
If no, How can I Create a staggered layout like Keep?
Thanks in Advance!

(See application for RecyclerView below in edits)
Like I mentioned in my comment, it's certainly fine to have separate adapters for all your Activities which use different data and views. As your app data and layouts get more complex, so does your code...that's just the way it is.
But if some of your Activities used similar data in their ListViews -- maybe, for example, two TextViews and an ImageButton -- you could save some effort by defining a single adapter that can be used for multiple Activities. You would then instantiate separate objects for each Activity, similar to the way you would create several ArrayAdapter<String> objects to populate multiple ListViews.
The BaseAdapter is a great class to extend when writing a custom adapter. It's flexible and allows you complete control over the data that's getting shown in your ListView. Here's a minimal example:
public class CustomBaseAdapter extends BaseAdapter {
private Context context;
private ArrayList<String> listData;
public CustomBaseAdapter(Context context, ArrayList<String> listData) {
this.context = context;
this.listData = listData;
}
#Override
public View getView(int position, View convertView, ViewGroup parent) {
if(convertView == null) {
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = inflater.inflate(R.layout.your_list_item_layout, parent, false);
//populate the view with your data -- some examples...
TextView textData = (TextView) convertView.findViewById(R.id.yourTextView);
textData.setText(listData.get(position));
ImageButton button = (ImageButton) convertView.findViewById(R.id.yourImageButton);
button.setOnClickListener(new View.OnClickListener() {
//...
//...
});
}
return convertView;
}
#Override
public Object getItem(int position) {
return 0;
}
#Override
public long getItemId(int position) {
return 0;
}
#Override
public int getCount() {
return listData.size();
}
}
So the key part of this code is obviously the getView() method, which is called every time the ListView needs some data to display. For efficiency, views are stored in something called a convertView so they may be re-used and not have to be inflated every time a view appears on the screen.
So what we do in getView() is first find out if the convertView exists. If it does, we just pass that back to the calling ListView because everything should already be instantiated and ready to go. If the convertView is null, it means the data hasn't been instantiated (or needs to be re-instantiated for whatever reason), and so we inflate a brand new view and populate it with our data.
So in the case of this example adapter above, if several of your Activities all displayed a single list of Strings, you could reuse this adapter for each one, passing in a different ArrayList<String> through the constructor each time you created a new object. But obviously you could pass in more than just Strings if you had more data to show. The level of complexity is up to you. And if the difference among your Activities was too great, I would just create custom versions of this class for all of them and just instantiate them and populate them however you'd like. It will keep all your data very organized and encapsulated.
Hope this helps! Feel free to ask questions for more clarification if you need it.
EDIT IN RESPONSE TO COMMENTS
Since you are using a RecyclerView instead of just plain ListViews (which I, for some reason, totally forgot) you could still do something very similar using a RecyclerView.Adapter<YourViewHolder> instead. The difference would be that instead of inflating the views in a getView() method, they are inflated inside your custom ViewHolder, which I assume you already have. The code might look something like this:
public class CustomRecyclerViewAdapter extends RecyclerView.Adapter<StringViewHolder> {
private final List<String> items;
public CustomRecyclerViewAdapter(ArrayList<String> items) {
this.items = items;
}
#Override
public StringViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
//So instead of inflating the views here or in a getView() like in
//in the BaseAdapter, you would instead inflate them in your custom
//ViewHolder.
return new StringViewHolder(parent);
}
#Override
public void onBindViewHolder(StringViewHolder holder, int position) {
holder.setModel(items.get(position));
}
#Override
public long getItemId(int position) {
return items.get(position).hashCode();
}
#Override
public int getItemCount() {
return items.size();
}
}

How to change the background of a listview in android based on it's position in the list?

I have a listview that is populated via an adapter. I need one of the items (which are just bits of text) in the listview to have a different background compared to the others (to mark it as the currently selected one).
I have all of the background logic, I just need a way to say listview.setBackgroundById(int position)
or something like that.
How do I do this?
This needs to be as simple as possible, 'cause all of the other things done in the Activity are currently working perfectly. :)
As asked, this is my Adapter that I'm using:
public class SampleAdapter extends ArrayAdapter<SampleItem> {
private String title;
public SampleAdapter(Context context) {
super(context, 0);
}
public View getView(final int position, View convertView, ViewGroup parent) {
if (convertView == null) {
convertView = LayoutInflater.from(getContext()).inflate(R.layout.row_station, null);
}
TextView title = (TextView)convertView.findViewById(R.id.station_name);
font.setFont(title, 2, getActivity());
title.setText(getItem(position).title);
RelativeLayout info = (RelativeLayout)convertView.findViewById(R.id.info_relative_button);
info.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
MainActivity.setCurrentTab(41);
MainActivity.setBackDisabled(true);
Log.e("current tab:",String.valueOf(MainActivity.getCurrentTab()));
Fragment fragment = new StationInfo();
FragmentManager fragmentManager = getFragmentManager();
fragmentManager.beginTransaction().replace(R.id.content_frame, fragment).commit();
UserManager.getInstance().setStationId(getItem(position).id);
}
});
return convertView;
}
}
The SampleItem has 2 String fields, title and id, it's very simple.

You need to use a custom list adapter and have it return views with your desired background. Create a class extending ListAdapter or any of the existing SimpleAdapter etc and override getView to inflate a suitable view for your element, and add any logic you need to set the background of that view.
There is no way to tell the listview itself to decorate some of its elements by id or position.
Update: I just noticed you added the list adapter code.
Since you are already implementing getView, to change the background of your element simply call convertView.setBackgroundColor, or have two different views inflated depending on the situation.
(BTW it's really bad practice to call static methods on your activity like in your onClickListener.)

In ListView adapter:
#Override
public View getView(int position, View view, ViewGroup viewGroup) {
if(view==null)
....
//for example every even list item to be grey, every odd to be white
if(((position+1)%2)==0)
view.setBackgroundColor(mContext.getResources().getColor(R.color.grey));
else view.setBackgroundColor(mContext.getResources().getColor(android.R.color.white));
Hope you get an idea...

ListView, and ArrayAdapter issue, How do I proceed?

I have a Product Class, Which has three fields:-
id
name
price
In my code I create a List<Product> productList = Collections.synchronizedList(new ArrayList<Product>());
This product list is used to create a ArrayAdapter<Product> adapter = ArrayAdapter<Product>(), I fill the productList in a separate thread and adapter is notified accordingly. It is working absolutely fine.
Now,
I want to change the color of the some specific products (say for price < 1000).
Each row of ListView should contain 4 elements product image,name, desc and price.
When User clicks the Product, in a context menu options i.e. buy Product, View Product should be displayed.
I have read few blogs and threads related to that. Still I cant decide where to begin, I read about the customization of the ArrayAdapter, overriding getView(), custom list filters etc. Which way will be the best for my requirement... in other words How can custom adapters and list filters benefit me ?

You should extend BaseAdapter and provide your own layout for each item (getView()). Don't forget to manage the view recycling and maybe use the ViewHolder paradigm.
EDIT
I didn't use a lot the ListAdpater, because it binds to a ListView only. Sometimes I need an adapter for a GridView, and the BaseAdapter gives me enough freedom for all use cases.
Example of BaseAdapter:
public class FanAdapter extends BaseAdapter {
private List<Fan> mFans;
private Activity mContext;
public FanAdapter(Activity context, List<Fan> fans) {
mContext = context;
mFans = fans;
}
private class ViewHolder {
public ImageView image;
public TextView firstName;
public TextView lastName;
}
#Override
public View getView(int position, View view, ViewGroup container) {
if (view == null) {
view = LayoutInflater.from(mContext).inflate(R.layout.fan_item, container, false);
}
ViewHolder viewHolder = (ViewHolder) view.getTag();
if(viewHolder == null){
viewHolder = new ViewHolder();
viewHolder.image = (ImageView) view.findViewById(R.id.image);
viewHolder.firstName = (TextView) view.findViewById(R.id.firstname);
viewHolder.lastName = (TextView) view.findViewById(R.id.lastname);
view.setTag(viewHolder);
}
// setting here values to the fields of my items from my fan object
viewHolder.firstName.setText(fan.getFirstName());
(...)
return view;
}
#Override
public int getCount() {
if (mFans != null) {
return mFans.size();
} else {
return 0;
}
}
#Override
public Object getItem(int position) {
return mFans.get(position);
}
#Override
public long getItemId(int position) {
return position;
}
}
You can use it with an Activity containing a ListView or a ListActivity (having in its layout a ListView with a special id):
<ListView
android:id="#id/android:list"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:cacheColorHint="#android:color/transparent" />
This way, your ListActivity that will inflate the view will be able to make a findViewById() call and getListView() will return this internal listView. It's a small hack, you can put your own listView with another id and make the findViewById() yourself. For The ListActivity, there's another hack: if the ListActivity finds an empty view with again a special id, it will be shown when the list is empty:
<include
android:id="#+id/empty"
layout="#layout/empty"
android:visibility="gone"
android:layout_gravity="center" />
Then on your listView, whether you used an Activity or ListActivity, you can set your adapter on the ListView:
getListView().setAdapter(new FanAdapter(this, myFanDataArray)));

in getView(...) method you have to check price and set color of row...
see this customized listview..
http://samir-mangroliya.blogspot.in/p/android-customized-listview.html
i set row color as per odd and even row and
you can set checking price...
if(price < 1000){
row.setBackgroundColor(Color.RED);
}else{
row.setBackgroundColor(Color.Yellow);
}

In android, how do you modify this code to populate two textviews instead of one?

I am trying to modify the sample code below. It currently populates a View that contains an imageview and a textview. I have added an additional textview to my XML layout and am trying to figure out how to replace the simple array with a hash map or even a multidimensional array to populate not just the imageview and the first textview but also the second one.
I would appreciate sample code that shows the entire process. Thanks!
public class DynamicDemo extends ListActivity {
TextView selection;
private static final String[] items={"lorem", "ipsum", "dolor",
"sit", "amet"}
#Override
public void onCreate(Bundle icicle) {
super.onCreate(icicle);
setContentView(R.layout.main);
setListAdapter(new IconicAdapter());
selection=(TextView)findViewById(R.id.selection);
}
public void onListItemClick(ListView parent, View v,
int position, long id) {
selection.setText(items[position]);
}
class IconicAdapter extends ArrayAdapter<String> {
IconicAdapter() {
super(DynamicDemo.this, R.layout.row, R.id.label, items);
}
public View getView(int position, View convertView,
ViewGroup parent) {
View row=super.getView(position, convertView, parent);
ImageView icon=(ImageView)row.findViewById(R.id.icon);
if (items[position].length()>4) {
icon.setImageResource(R.drawable.delete);
}
else {
icon.setImageResource(R.drawable.ok);
}
return(row);
}
}
}

The easiest thing to do is use an ArrayAdapter<MyDataObject> where
public class MyDataObject {
public String string1;
public String string2;
// any other useful attributes
}
And then you would change items to a MyDataObject[] items stored in your class, and instead of doing super.getView(index) you'd do items[index] (which would yield a MyDataObject) and use that data instead.
Also, importantly: you should use the convertView. And possibly the ViewHolder pattern.
Edit: At OP's request, a little more elaboration. Note that this uses the convertView pattern but not the ViewHolder pattern (you should be able to adopt that fairly easily).
In your Adapter, you'd change getView() as follows:
public View getView(int position, View convertView,
ViewGroup parent) {
ViewGroup row;
if(convertView == null){
// create your view here.
row = getLayoutInflater().inflate(R.layout.row);
} else {
row = convertView;
}
// note: when you implement ViewHolder, the ViewHolder will
// hold this reference so that you don't need to look it up every time.
ImageView icon=(ImageView)row.findViewById(R.id.icon);
// here you're employing the "items" array that you were using
// before, except now it contains MyDataObjects. pick out the
// string (or other data you want to check) from the resulting MyDataObject,
// and see if it's longer than 4 characters.
MyDataObject objectAtThisPosition = items[position];
if (objectAtThisPosition.string1.length()>4) {
icon.setImageResource(R.drawable.delete);
}
else {
icon.setImageResource(R.drawable.ok);
}
// Do whatever else you want to with objectAtThisPosition.
return(row);
}
That's it for the easy way, and quite similar to what you have.
Some more detail; if you don't care, skip it. :)
I know that Adapters can seem magical, so in the interest of showing how ListView adapters work, here's an example using a List instead of an Array, so we can remove any magic that ArrayAdapter does with the array behind the scenes. I use a List because they can be more versatile for whatever you're trying to accomplish (ArrayList or LinkedList or what-have-you).
To use a List you'd have the following in your Activity:
private List<MyDataObject> myList = new ArrayList<MyDataObject>();
And instead of items[position] you'd use
MyDataObject objectAtThisPosition = myList.get(position);
If you want to change your data set dynamically, you should probably use this approach (keeping myList at the Activity level) instead of using an Array and an ArrayAdapter. That would mean you'd need to change from extending ArrayAdapter<String> to just extending BaseAdapter<MyDataObject> (most of the methods in BaseAdapter are trivial to implement) since our data size, for example, would be determined by our list, and not the ArrayAdapter's array.
I know that's kind of a fire hose, but let me know if you have any questions!

Use a separator in string, like \t.
Or use an array of straing arrays.
Or use an array of Pair<String, String>.
Or use an array of custom objects.

BaseAdapter causing ListView to go out of order when scrolled

I'm having problems with some BaseAdapter code that I adapted from a book. I've been using variations of this code all over the place in my application, but only just realized when scrolling a long list the items in the ListView become jumbled and not all of the elements are displayed.
It's very hard to describe the exact behavior, but it's easy to see if you take a sorted list of 50 items and start scrolling up and down.
class ContactAdapter extends BaseAdapter {
ArrayList<Contact> mContacts;
public ContactAdapter(ArrayList<Contact> contacts) {
mContacts = contacts;
}
#Override
public int getCount() {
return mContacts.size();
}
#Override
public Object getItem(int position) {
return mContacts.get(position);
}
#Override
public long getItemId(int position) {
return position;
}
#Override
public View getView(int position, View convertView, ViewGroup parent) {
View view;
if(convertView == null){
LayoutInflater li = getLayoutInflater();
view = li.inflate(R.layout.groups_item, null);
TextView label = (TextView)view.findViewById(R.id.groups_item_title);
label.setText(mContacts.get(position).getName());
label = (TextView)view.findViewById(R.id.groups_item_subtitle);
label.setText(mContacts.get(position).getNumber());
}
else
{
view = convertView;
}
return view;
}
}

You are only putting data in the TextView widgets when they are first created. You need to move these four lines:
TextView label = (TextView)view.findViewById(R.id.groups_item_title);
label.setText(mContacts.get(position).getName());
label = (TextView)view.findViewById(R.id.groups_item_subtitle);
label.setText(mContacts.get(position).getNumber());
to be after the if/else block and before the method return, so you update the TextView widgets whether you are recycling the row or creating a fresh one.

To further clarify the answer of CommonsWare, here is some more info:
The li.inflate operation (needed here for parsing of the layout of a row from XML and creating the appropriate View object) is wrapped by an if (convertView == null) statement for efficiency, so the inflation of the same object will not happen again and again every time it pops into view.
HOWEVER, the other parts of the getView method are used to set other parameters and therefore should NOT be included within the if (convertView == null){ }... else{ } statement.
In many common implementation of this method, some textView label, ImageView or ImageButton elements need to be populated by values from the list[position], using findViewById and after that .setText or .setImageBitmap operations.
These operations must come after both creating a view from scratch by inflation and getting an existing view if not null (e.g. on a refresh).
Another good example where this solution is applied for a ListView ArrayAdapter appears in https://stackoverflow.com/a/3874639/978329