I've created CardView inside RecyclerView.

My XML for CardView looks like this:

<?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">

<TextView
    android:id="@ id/textView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="TextView" />
</androidx.cardview.widget.CardView>

I've created the Adapter and successfully shown the data to CardView that inside RecyclerView.

But I failed when I added Button in my activity_main.xml to change size of textView. My program looks like this:

textView =findViewById(R.id.textView);
button = findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {
        textView.setTextSize(42);
    }
});

The error message is:

 2022-04-18 13:28:47.264 3144-3144/com.example.myapplication 
 E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.myapplication, PID: 3144
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setTextSize(float)' on a null object reference
    at com.example.myapplication.MainActivity$1.onClick(MainActivity.java:39)

How to solve those problems?

CodePudding user response：

To Update text of recycleview item

1. get position of that item in Recycleview

2. I am assuming you have a list of items that you passed to adapter , get that item using position you get from step 1 e.g list.get(postion)

3. now update this item field that shows text on item

4. user adapter.notifyItemChanged(postion , updatedItem

Pseudo Kotlin code-->

fun updateTextView(position:Int){

  val item = list[position]
  item.text = "new_text"
  adapter.notifyItemChanged(postion , item)

}

CodePudding user response：

You cannot access TextView directly in RecyclerView this way. You should get a ViewHolder via adapter and change it there.

val item = adapter.get(1) // Or another method to get an item from a collection

See How can I access the viewholder of an item in a recycler view? to access ViewHolder directly. Or change TextView in a listener bound in onBindViewHolder.

CodePudding user response：

Don't Initialize your textView in MainActivity

Do it in your adapter

Like below example :

<<<<<<<<<>>>>>>>

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder> {

private Context mContext;
private List<ModelRecycler> mData;

public MyAdapter (Context mContext, List<ModelRecycler> mData) {
    this.mContext = mContext;
    this.mData = mData;
}

@NonNull
@Override
public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
    View v;
    LayoutInflater inflater = LayoutInflater.from(mContext);
    v = inflater.inflate(R.layout.list_item, parent, false);
    return new MyViewHolder(v);
}

@Override
public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {

    holder.textView.setTextSize(42);
   
}

@Override
public int getItemCount() {
    return mData.size();
}

public static class MyViewHolder extends RecyclerView.ViewHolder {

    TextView textView;
   
    public MyViewHolder(@NonNull View itemView) {
        super(itemView);
        textView = itemView.findViewById(R.id.textView);
        
    }
}

}