Develop Reference

getView-method in customized Adapter is not called

im working on a tank-game. in this tank-game i want to display the items which the player can use(shild,firework,atombomb)i want to realise this with a listview and a arraya-dapter. i've made a customized ArrayAdapter like i found it in much answers but it didnt work. The list is not there after i set the adapter. After i debug the project i came to the conclusion that the getView-method in the adapter class isnt called
why?
This is my adapter class
public class Adapter extends ArrayAdapter {
private Context context;
private ArrayList<Item> items;
public Adapter(#NonNull Context context, ArrayList<Item> items) {
super(context, R.layout.listview_item);
this.context = context;
this.items = items;
}
#NonNull
#Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder viewHolder = new ViewHolder();
if(convertView == null) {
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = inflater.inflate(R.layout.listview_item, parent, false);
viewHolder.imageView = convertView.findViewById(R.id.imageView);
convertView.setTag(viewHolder);
}else{
viewHolder = (ViewHolder) convertView.getTag();
}
viewHolder.imageView.setImageBitmap(items.get(position).getImageView());
return convertView;
}
static class ViewHolder{
ImageView imageView;
}
}
Here i want to set the adapter
public void createList(ListView listView){
Adapter adapter = new Adapter(context,tanks.get(currentTank).getItems());
listView.setAdapter(adapter);
}

public Adapter(#NonNull Context context, ArrayList<Item> items) {
super(context, R.layout.listview_item);
this.context = context;
this.items = items;
}
Instead of this try this :
public MyCustomListAdapter(Context context,int resource, ArrayList<Item> items)
{
super(context,resource,list);
this.context= context;
this.resource=resource;
this.list=list;
}
Also in your main class write this code:
Adapter adapter = new Adapter(context,R.layout.<Thename of your layout>,tanks.get(currentTank).getItems());

How to remove a item in listview?

I am creating a playlist with 2 lines of name and genre, how to I can delete it.
This is MainActivity :
String[] gene, sl;
...
adp = new Adapter(MainActivity.this, gene, sl);
lv.setAdapter(adp);
This is Adapter
public class Adapter extends ArrayAdapter<String> {
private final Activity context;
private final String[] gene;
private final String[] sl;
SharedPreferences preferences;
public Adapter(Activity context, String[] gene ,String[] sl) {
super(context, R.layout.activity_m , gene);
this.context = context;
this.gene = gene;
this.sl = sl;
}
private class ViewHolder{
TextView txtgene, txtsl;
}
#Override
public View getView(final int position, View view, ViewGroup parent) {
ViewHolder holder;
if (view == null) {
LayoutInflater inflater = context.getLayoutInflater();
view = inflater.inflate(R.layout.activity_m, null, true);
holder = new ViewHolder();
holder.txtgene = (TextView) view.findViewById(R.id.txtgene);
holder.txtsl = (TextView) view.findViewById(R.id.txtsl);
view.setTag(holder);
}else{
holder = (ViewHolder) view.getTag();
}
if (gene[position] != null) {
holder.txtgene.setText(gene[position]);
}
holder.txtsl.setText(sl[position]);
return view;
}
}
How to remove an item when you know its exact position ?
Thank !

You are using the ArrayAdapter constructor that takes an array. This in turn will create an immutable List internal to the ArrayAdapter. So, you will not be able to modify your adapter going this route.
Instead, make a new ArrayList from your array and call the ArrayAdapter constructor that takes a List.
So, change the super call in your Adapter constructor to this:
super(context, R.layout.activity_m, new ArrayList<>(Arrays.asList(gene)));
And then, when you want to remove an item given it's position, do this:
adp.remove(getItem(position));
PS: You should consider refactoring your gene and sl arrays into a class and then use it as the type of your List.

Holder vs RecylerView.ViewHolder

I have ListView with Adapter, and also use holder. but later I read about recyclerView.ViewHolder and now confused, Is it different with the one I've been using right now? I mean for the optimization purpose, I want to know if using holder only is not good enough without using recyclerView.
public class NewsAdapter extends ArrayAdapter<News> {
Context context;
List<News> myList;
public NewsAdapter(Context context, int resource, List<News> objects) {
super(context, resource, objects);
this.context = context;
this.myList = objects;
}
#Override
public News getItem(int position) {
if(myList != null)
return myList.get(position);
return null;
}
#Override
public View getView(int position, View convertView, ViewGroup parent) {
Holder holder;
if (convertView == null){
LayoutInflater inflater = (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = inflater.inflate(R.layout.list_news, null);
holder = new NewsAdapter.Holder();
holder.title = (TextView)convertView.findViewById(R.id.textViewTitle);
holder.datePosted = (TextView)convertView.findViewById(R.id.textViewDate);
holder.imageView = (ImageView)convertView.findViewById(R.id.imageViewThumbnailpic);
convertView.setTag(holder);
}else{
holder = (Holder)convertView.getTag();
}
News news = getItem(position);
holder.title.setText(news.getTitle());
holder.datePosted.setText(news.getDatePost());
Picasso.with(context)
.load(news.getImgUrl())
.placeholder(R.drawable.coin25)
.error(R.drawable.hnbspic)
.into(holder.imageView);
return convertView;
}
private class Holder{
ImageView imageView;
TextView title;
TextView datePosted;
}
}

It's better to use Recyclerview because it has been optimized for various scenarios and not just for View holder pattern like it give the option for determining how your item should be laid out or like what should be the animation or custom drawing in each item.You can read more this medium post

How to add arrayList<model> items to an listView

I want to add every element of an arrayList to a listView ,Here I am passing an arrayList to the adapter which contains package name and size ,
How to iterate and display all the items in the listView.
public class CCacheAdapter extends ArrayAdapter<CCacheInfo>
{
private ArrayList<CCacheInfo> arrayList;
private Context mContext;
public CCacheAdapter(Context context, ArrayList<CCacheInfo> cacheInfos)
{
super(context,0, cacheInfos);
mContext=context;
arrayList=cacheInfos;
}
#NonNull
#Override
public View getView(int position, View convertView, ViewGroup parent)
{
CCacheInfo cCacheInfo = getItem(position);
ViewHolder oViewHolder;
if (convertView == null)
{
convertView = LayoutInflater.from(getContext()).inflate(R.layout.cache_items, parent, false);
oViewHolder =new ViewHolder();
oViewHolder.mPackageName = (TextView)convertView.findViewById(R.id.package_name);
oViewHolder.mPackageSize = (TextView)convertView.findViewById(R.id.package_size);
oViewHolder.mPackageIcon = (ImageView)convertView.findViewById(R.id.appIcon);
oViewHolder.mCheckbox = (CheckBox)convertView.findViewById(R.id.checkbox);
convertView.setTag(oViewHolder);
}else
{
oViewHolder = (ViewHolder)convertView.getTag();
}
oViewHolder.mPackageName.setText(cCacheInfo.m_szAppName);
oViewHolder.mPackageSize.setText(CCleanTool.formatShortFileSize(mContext, cCacheInfo.m_nSize));
return convertView;
}
private class ViewHolder
{
TextView mPackageName;
TextView mPackageSize;
CheckBox mCheckbox;
ImageView mPackageIcon;
}
}

Just set the adapter to ListView, like the following
ArrayList<CCacheInfo> cacheInfos = ... // you get your data from somewhere
ListView listView = (ListView) findViewById(R.id.list_view);
CCacheAdapter adapter = new CCacheAdapter(this, cacheInfos);
listView.setAdapter(adapter);

why every example that extends ArrayAdapter saves the list as private?

why in every example i see that extends the class ArrayAdapter it overrides the constructor that accepts T[] objects and references its own private variable to that and uses the referenced variable in the override of getView?
how can this be dynamic adding of objects?
will values be updated when a new item is added to the ArrayAdapter using add method?
can i instead of implementing my own adapter just use addheaderview in listview?
public class MySimpleArrayAdapter extends ArrayAdapter<String> {
private final Context context;
private final String[] values;
public MySimpleArrayAdapter(Context context, String[] values) {
super(context, R.layout.rowlayout, values);
this.context = context;
this.values = values;
}
#Override
public View getView(int position, View convertView, ViewGroup parent) {
LayoutInflater inflater = (LayoutInflater) context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View rowView = inflater.inflate(R.layout.rowlayout, parent, false);
TextView textView = (TextView) rowView.findViewById(R.id.label);
ImageView imageView = (ImageView) rowView.findViewById(R.id.icon);
textView.setText(values[position]);
// change the icon for Windows and iPhone
String s = values[position];
if (s.startsWith("iPhone")) {
imageView.setImageResource(R.drawable.no);
} else {
imageView.setImageResource(R.drawable.ok);
}
return rowView;
}
}