When I add an item by button Scan Now, the public double sumCost value incrementes by the cost value in the AddItem method and then TextView(android:id="@ id/SumText") assigns this value. And How to decrease sumCost by the number that is in cost and set new text in TextView when pressing the Delete button? Thanks for any help
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My full code:
MainActivity:
package com.example.testfirst;
...
public class MainActivity extends AppCompatActivity {
TextView sumText;
Button buttonAdd;
List<Contact> contacts = new LinkedList<>();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_users);
buttonAdd = (Button) findViewById(R.id.scanBtn);
sumText = (TextView) findViewById(R.id.SumText);
buttonAdd.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
AddItem("Tom", 2.45);
sumText.setText(Double.toString(sumCost));
}
});
}
public void AddItem(String name, double cost){
sumCost = cost;
RecyclerView rvContacts = (RecyclerView) findViewById(R.id.recyclerView);
ContactsAdapter adapter = new ContactsAdapter(contacts);
rvContacts.setAdapter(adapter);
rvContacts.setLayoutManager(new LinearLayoutManager(this));
contacts.add(new Contact(name,Double.toString(cost)));
}
public double sumCost = 0;
}
Contact(Model class):
...
public class Contact {
private String mName;
private String mCost;
public Contact(String name, String cost) {
mName = name;
mCost = cost;
}
public String getName() {
return mName;
}
public String getCost() {
return mCost;
}
}
ContactsAdapter:
...
public class ContactsAdapter extends RecyclerView.Adapter<ViewHolder>{
@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
Context context = parent.getContext();
LayoutInflater inflater = LayoutInflater.from(context);
View contactView = inflater.inflate(R.layout.item_contact, parent, false);
return new ViewHolder(contactView).linkAdapter(this);
}
///////////////
@NonNull
@Override
public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
Contact contact = mContacts.get(position);
TextView textViewId = holder.nameId;
textViewId.setText(contact.getName());
TextView textViewCost = holder.nameCost;
textViewCost.setText(contact.getCost());
}
@Override
public int getItemCount() {
return mContacts.size();
}
List<Contact> mContacts;
public ContactsAdapter(List<Contact> contacts) {
mContacts = contacts;
}
}
class ViewHolder extends RecyclerView.ViewHolder {
private ContactsAdapter adapter;
public TextView nameId;
public TextView nameCost;
public ViewHolder(@NonNull View itemView) {
super(itemView);
nameId = (TextView) itemView.findViewById(R.id.text);
nameCost = (TextView) itemView.findViewById(R.id.textCost);
itemView.findViewById(R.id.delete).setOnClickListener(view -> {
adapter.mContacts.remove(getAdapterPosition());
adapter.notifyItemRemoved(getAdapterPosition());
});
}
public ViewHolder linkAdapter(ContactsAdapter adapter){
this.adapter = adapter;
return this;
}
}
item_contact.xml:
<?xml version="1.0" encoding="utf-8"?>
<androidx.cardview.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_margin="10dp"
app:cardCornerRadius="10dp"
app:cardElevation="5dp"
app:contentPadding="5dp">
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal">
<TextView
android:id="@ id/text"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:text="@string/app_name"
android:textSize="20sp" />
<TextView
android:id="@ id/textCost"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@ id/text"
android:text="@string/app_name"
android:textSize="20sp" />
<Button
android:id="@ id/delete"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_alignParentEnd="true"
android:layout_marginTop="3dp"
android:layout_marginEnd="3dp"
android:text="Delete" />
</RelativeLayout>
</androidx.cardview.widget.CardView>
activity_users.xml:
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity"
android:orientation="vertical"
android:padding="10dp">
<TextView
android:id="@ id/SumText"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:text="0.00"
android:textSize="30sp"/>
<Button
android:id="@ id/scanBtn"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Scan now"
android:textSize="30sp"
android:layout_gravity="center_horizontal"/>
<androidx.recyclerview.widget.RecyclerView
android:id="@ id/recyclerView"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1"/>
</LinearLayout>
</androidx.constraintlayout.widget.ConstraintLayout>
CodePudding user response：
One easy way to do that would be do add a "Decrementer" interface in the adapter that it can call to decrement the total cost, like this:
// Define the interface
public interface Decrementer {
void onDelete(double cost);
}
// Define an instance of the interface to hold
private final Decrementer mDecrementer;
// Pass in a decrementer at construction
public ContactsAdapter(List<Contact> contacts, Decrementer decr) {
mContacts = contacts;
mDecrementer = decr;
}
@NonNull
@Override
public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
// get views and such ...
// Call the decrementer method when the button is clicked
// Could set this in onBindViewHolder, or pass the decrementer
// into the ViewHolder itself and use it there.
deleteButton.setOnClickListener(view -> {
int pos = holder.getAdapterPosition();
Contact c = mContacts.get(pos);
// add getCostAmount to return a double, or better yet, just
// store it as a Double instead of a string in Contact
mDecrementer.onDelete(c.getCostAmount());
mContacts.remove(pos);
notifyItemRemoved(pos);
});
}
and you would define the Decrementer when you create the adapter so it can access the Activity class members, like this:
ContactsAdapter adapter = new ContactsAdapter(contacts, new ContactsAdapter.Decrementer() {
@Override
public void onDelete(double cost) {
sumCost -= cost;
// change activity TextViews and such here too
sumText.setText(Double.toString(sumCost));
}
});
Side note: you don't need to create a whole new adapter every time you add an item, just add it to the contacts array and call an appropriate notifyDataSetChanged method on the existing adapter.
private ContactsAdapter adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_users);
//...
RecyclerView rvContacts = (RecyclerView) findViewById(R.id.recyclerView);
ContactsAdapter adapter = new ContactsAdapter(contacts);
rvContacts.setAdapter(adapter);
rvContacts.setLayoutManager(new LinearLayoutManager(this));
}
public void AddItem(String name, double cost){
sumCost = cost;
contacts.add(new Contact(name,Double.toString(cost)));
adapter.notifyDataSetChanged(); // or a less expensive notify call
}