Develop Reference

Do I use ViewHolder correctly? Everithing is worked, but i still have doubts with the ListView optimization with holder recycler

I am just adapting my custom adapter code with ViewHolder so that i can optimize my list view with a recycler, but i am not sure if i do it right.
My view holder class:
public class ViewHolderTask {
int positionHolder;
TextView nameHolder;
TextView timeHolder;
TextView sessionHolder;
TextView dateHolder;
FloatingActionButton mFabTaskHolder;
public ViewHolderTask(View v, int position) {
this.positionHolder = position;
this.nameHolder = v.findViewById(R.id.taskNameText);
this.timeHolder = v.findViewById(R.id.timeTextView);
this.sessionHolder = v.findViewById(R.id.textViewSession);
this.dateHolder = v.findViewById(R.id.dateTextView);
this.mFabTaskHolder = v.findViewById(R.id.myFabTask);
}
My custom adapter class:
#NonNull
#Override
public View getView(int position, #Nullable View convertView, #NonNull ViewGroup parent) {
ViewHolderTask holder;
if(convertView == null){
LayoutInflater inflater = (LayoutInflater) context.getSystemService(
Context.LAYOUT_INFLATER_SERVICE );
convertView = inflater.inflate(R.layout.task_row, parent, false);
holder = new ViewHolderTask(convertView, position);
convertView.setTag(holder);
}else{
holder = (ViewHolderTask) convertView.getTag();
}
Task task = taskArrayList.get(position);
//set the configurations
holder.getTimeHolder().setText(getTimeString(task.getTime()));
holder.getNameHolder().setText(task.getName());
holder.getDateHolder().setText(getDateString(task.getDate()));
holder.getSessionHolder().setText(getSessionString(task.getSession()));
//Set the FAB listener
addFabListener(holder.getmFabTaskHolder(), position);
//set the clicked background
if(TaskActivity.getIsClicked() && TaskActivity.getPositionClicked()-1 == position){
convertView.setBackgroundResource(R.color.backgroundSelectedItem);
}
return convertView;
}
Do I use it right?

Seems to be fine for me other than this portion of the code
//set the clicked background
if(TaskActivity.getIsClicked() && TaskActivity.getPositionClicked()-1 == position){
convertView.setBackgroundResource(R.color.backgroundSelectedItem);
}
You might need to reset the background resource back to default for the item which is not clicked. maybe you have to add "else" part to the "if"

Wrong number of the element in Adapter at GridView

I created my own adapter that extend BaseAdapter and I use it for GridView. I want to get the number of element and put it into TextView. I did it in my adapter:
#Override
public View getView(int position, View convertView, ViewGroup parent) {
LayoutInflater inflater = (LayoutInflater) context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View gridView;
if(convertView == null){
gridView = new View(context);
gridView = inflater.inflate(R.layout.grid_element, null);
ImageView logo = (ImageView) gridView.findViewById(R.id.grid_logo);
TextView tv = (TextView) gridView.findViewById(R.id.grid_textView1);
tv.setText(level+position);
}
else
gridView = convertView;
return gridView;
}
It seems to be good until I get elements that are not in the screen in launch:
The position is like reseted.
How can I do it properly?

You were not setting the TextView properly when convertView was not null. Try this:
if (convertView == null) {
gridView = inflater.inflate(R.layout.grid_element, null);
} else {
gridView = convertView;
}
ImageView logo = (ImageView) gridView.findViewById(R.id.grid_logo);
TextView tv = (TextView) gridView.findViewById(R.id.grid_textView1);
tv.setText(level + position);

May help new Visitors.
You have to know two main things :
You need to check if convertView is null, in order to know if that row in your list is not created yet (convertView = null) or is being recycled by the adapter (convertView != null). This is called the Recycling process.
Another important thing to know is the View Holder Pattern. Calling findViewById() on each row of getView() method is to heavy for list populating and slows down scrolling performance. To avoid that, create a static class with some views as class fields. Than use findViewById() if the view is being created (convertView == null), and get it back from getTag() method when it's being recycled
`
static class ViewHolder {
TextView text;
ImageView icon;
}
ViewHolder holder;
if(convertView == null) {
convertView = inflater.inflate(resource, root);
holder = new ViewHolder();
holder.icon = (ImageView) convertView.findViewById(R.id.listitem_image);
holder.text = (TextView) convertView.findViewById(R.id.listitem_text);
holder.timestamp = (TextView) convertView.findViewById(R.id.listitem_timestamp);
holder.progress = (ProgressBar) convertView.findViewById(R.id.progress_spinner);
convertView.setTag(holder);
}
holder = (ViewHolder) convertView.getTag();
// Set here your view's content :
holder.text.setText("Sample");
// ...

Changing the size of cells in grid view?

I have a gridview in Android which is populated by a custom view which inherits from imagebuttons.
What I would like to do is modify the size of the imagebuttons inside the gridview as well as their padding between cells.
Here is my getView() code. I've tried using layouts but can't because I don't have access to the parent view.
public View getView(int position, View convertView, ViewGroup parent) {
LayoutInflater inflater = (LayoutInflater) context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
if (image == null)
image = BitmapFactory.decodeResource(context.getResources(), R.drawable.dollar);
ExpenseIcon ic = new ExpenseIcon(context);
ic.setImageBitmap(image);
return ic;
}
How do I do that?

You can set the with with setColumnWidth(int) or set the column count by calling setNumColumns(int) depending on what you extactly trying. By the way you can also set that values by xml (android:columnWidth and android:numColumns).
For the spacing you can use android:horizontalSpacing or setHorizontalSpacing(int) and android:verticalSpacing or setVerticalSpacing(int).
For controling the highe you need to change your getView function:
public YourConstructor() {
// inflater should be a private member variable
inflater = (LayoutInflater)context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
// other code...
}
public View getView(int position, View convertView, ViewGroup parent) {
if(convertView == null) {
// create new one and put it into convertView. e.g.:
convertView = new ExpenseIcon(context);
AbsListView.LayoutParams lp = new AbsListView.LayoutParams(HEIGHT,WIDTH);
convertView.setLayoutParams(lp);
}
// set the image to the currient convertView. e.g.:
((ExpenseIcon)convertView).setImageBitmap(image);
return convertView;
}

Create an XML and inflate.I gave sample to use in getview...Set imagesize in the layout..
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder;
if (convertView == null) {
convertView = mInflater.inflate(R.layout.grid_item, null);
holder = new ViewHolder();
holder.image = (ImageView) convertView.findViewById(R.id.grid_item_image);
convertView.setTag(holder);
}else {
holder = (ViewHolder) convertView.getTag();
}
holder.image.setImageResource(list.get(position).getIconid());
return convertView;
}
static class ViewHolder {
ImageView image;
}

Targeting strings in a listview android

listView.setOnItemClickListener(new OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
if(position == 1 ){
Toast.makeText(getApplicationContext(),
"Click ListItem Number " + position,
Toast.LENGTH_LONG)
.show();
}else{
}
i have a list view from a custom adapter that works fine and when i click an item it gets the correct position.
how can i exract a field views text out of the position. ie
holder.txtDesc = (TextView) convertView.findViewById(R.id.desc);
i want to target the desc field out of the position listem that i clicked..
i know you can use hash mapping but is there a way to just target a field view on item click by its list position? I know this is "webby" but I am sure java has the same flexibility
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder = null;
RowItem rowItem = getItem(position);
LayoutInflater mInflater = (LayoutInflater) context
.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
if (convertView == null) {
convertView = mInflater.inflate(R.layout.list_item, null);
holder = new ViewHolder();
holder.txtDesc = (TextView) convertView.findViewById(R.id.desc);
holder.txtTitle = (TextView) convertView.findViewById(R.id.title);
convertView.setTag(holder);
} else
holder = (ViewHolder) convertView.getTag();
holder.txtDesc.setText(rowItem.getDesc());
holder.txtTitle.setText(rowItem.getTitle());
return convertView;
}

how can i exract a field views text out of the position. ie
holder.txtDesc = (TextView) convertView.findViewById(R.id.desc);
Inside onItemClick() you can use:
TextView textview = (TextView) view.findViewById(R.id.desc);
// Now use textView.getText().toString() to get the description
Since convertView from the Adapter is the same object as view in the Listener.

Can't you just call adapter.getItem(position)?

If you need only text current item use BaseAdapter and you can get text following way:
(String) adapter.getItem(position);
If you need TextView object current item you can get TextView following way:
listView.setOnItemClickListener(new OnItemClickListener() {
#Override
public void onItemClick(AdapterView parent, View view, int position, long id) {
ViewHolder holder = (ViewHolder)view;
TextView txtDescTV = holder.txtDesc;
}
}

Populating Custom ArrayAdapters

I have made my own CustomArrayAdapter to show list of Brazilian Restaurants. I have overidden the GetView method to make my own custom view.
private class MyAdapter extends ArrayAdapter<String> {
public MyAdapter(Context context, int resource, int textViewResourceId,
String[] strings) {
super(context, resource, textViewResourceId, strings);
// TODO Auto-generated constructor stub
}
#Override
public View getView(int position, View convertView, ViewGroup parent) {
LayoutInflater inflater = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View row = inflater.inflate(R.layout.list_item, parent,false);
String [] items= getResources().getStringArray(R.array.locations_array);
TextView tv= (TextView) row.findViewById(R.id.textView1);
ImageView iv = (ImageView) row.findViewById(R.id.imageView1);
tv.setText(items[position]);
iv.setImageResource(R.drawable.brazil);
return row;
}
}
Currently this new GetView class is pulling in a text string from a resource xml file and putting it into the list item.
If I wanted to incorporate an array of extra data generated within the app, I assume that I don't do the array generating in the GetView class as this will be recreated each time a new row is made.
Where do I put the code to make the array, and how do I call this data into the GetView code above?

It's worth pointing out that for better performance you should be making use of the convertView variable passed into the getView() method.
The use of convertView allows you to re-use list item views instead of creating new ones which has a heavy performance hit. If you have a large data set or value performance in your app, you would do well to check out the documentation for getView()
Your code would then look something more like this:
...
//it's also worth moving these methods to your constructor so they aren't called every time getView() for better performance
LayoutInflater inflater = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);
String [] items= getResources().getStringArray(R.array.locations_array);
#Override
public View getView(int position, View convertView, ViewGroup parent) {
if(convertView == null)
convertView = inflater.inflate(R.layout.list_item, parent, false);
TextView tv= (TextView) convertView.findViewById(R.id.textView1);
ImageView iv = (ImageView) convertView.findViewById(R.id.imageView1);
tv.setText(items[position]);
iv.setImageResource(R.drawable.brazil);
return row;
}
...

Building on #CodeDownZero's answer, I highly recommend you adopt the ViewHolder pattern, and definitely recycle your listviews (using convertview).
...
#Override
public View getView(int position, View convertView, ViewGroup parent) {
View view = null;
if (convertView == null) {
LayoutInflater inflater = (LayoutInflater) getSystemService
(Context.LAYOUT_INFLATER_SERVICE);
view = inflater.inflate(textViewResourceId, parent, false);
final ViewHolder viewHolder = new ViewHolder();
viewHolder.tv1 = (TextView) view.findViewById(R.id.textView1);
viewHolder.tv2 = (TextView) view.findViewById(R.id.textView2);
view.setTag(viewHolder);
} else {
view = convertView;
}
ViewHolder holder = (ViewHolder) view.getTag();
MyDataClass data = this.getItem(position);
holder.tv1.setText(data.street);
holder.tv2.setText(data.name);
return view;
}
...
private class ViewHolder {
private TextView tv1;
private TextView tv2;
}

You can base an ArrayAdapter on a custom class instead of string. Here is an example:
public class MyDataClass {
public String street;
public String name;
}
private class MyAdapter extends ArrayAdapter<MyDataClass> {
#Override
public View getView(int position, View convertView, ViewGroup parent) {
LayoutInflater inflater = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View row = inflater.inflate(R.layout.list_item, parent,false);
TextView tv1= (TextView) row.findViewById(R.id.textView1);
TextView tv2= (TextView) row.findViewById(R.id.textView2);
MyDataClass data = this.getItem(position);
tv1.setText(data.street);
tv2.setText(data.name);
return row;
}
}
To populate the Adapter with data you can use this snippet in the OnCreate method of the Activity:
..
MyAdapter adapter = new MyAdapter();
MyDataClass lData = new MyDataClass(); // here was a mistake
lData.name = "MyName";
lData.street = "MyRoad";
adapter.Add(lData);
..
ListView.Adapter=adapter; // where Listview is the Listview