How to inflate Button to LinearLayout progmatically in this case?

Question

My task is to generate several amount of buttons with fixed width and height.I decided to store these buttons in some ArrayList to use in the future. This is how I do it:

 for(int i = 1 ; i<=n; i++)
{
 Button place = new Button(this.context) ;

      place.setTextColor(ContextCompat.getColor
     (this.context,R.color.background_color));

    place.setTypeface(typefaceForPlaces);

    place.setId(i+0);

    place.setBackgroundResource(R.drawable.real_place_background);

    place.setLayoutParams(new 
    LinearLayout.LayoutParams(65,65));

    places.add(place);

}

But problem is here place.setLayoutParams(newLinearLayout.LayoutParams(65,65));

Here,width and height is set in pixels. But I need dp. I know code that converts dp to pixels, but I do not think that it is good solution. Now,I have an idea to create some layout and store there my button's shape. Here is my layout for this called place_button.xml:

    <?xml version="1.0" encoding="utf-8"?>
   <Button 
    xmlns:android="http://schemas.android.com/apk/res/android"    
    android:id="@+id/button_id"
    android:layout_width="50dp" 
    android:layout_height="50dp"
    android:background="@drawable/real_place_background"
    android:textColor="#202020">
    </Button>

And I created some View and inflated that button to this view. After that, I got the button above by its id and save it to another button,because I need a lot of such buttons. Then I needed to change new button's id. But i got following error:

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.incubic.abay.clasico/com.incubic.abay.clasico.GameActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setId(int)' on a null object reference

Below is my code:

 private void generatePlaces() {
        View place_view = LayoutInflater.from(getContext()).inflate(R.layout.place_button,null);
        for(int i = 1 ; i<=n; i++)
        {

            Button place = (Button)place_view.findViewById(R.id.button_id);
            place.setId(i+0);
            place.setTypeface(typefaceForPlaces);
            places.add(place) ;
           }
    }

Everything happens in Fragment. generatePlaces method is called after onViewCreated. How to solve my problem?

Is there an element with "button_id" as id in your place_button.xml? — Abhishek Patel, Jul 25 '17 at 15:11

Ayaz Alifov · Accepted Answer · 2017-07-25T15:36:17.770

Probably you have an issue due to absence of a Button id

<?xml version="1.0" encoding="utf-8"?>
<Button
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/button_id"
        android:layout_width="50dp"
        android:layout_height="50dp"
        android:background="@drawable/real_place_background"
        android:textColor="#202020"/>

UPDATE:

When you do inflation, you already get your Button view, no need to do findViewById.

In general I don't think inflating a view in your case is a good approach. Better create buttons:

private void generatePlaces()
{
    for (int i = 1; i <= n; i++)
    {
        Button place = new Button(this.context);

        place.setTextColor(ContextCompat.getColor(this.context, R.color.background_color));
        place.setTypeface(typefaceForPlaces);
        place.setId(i + 0);
        place.setBackgroundResource(R.drawable.real_place_background);
        place.setLayoutParams(new LinearLayout.LayoutParams(dpToPx(50), dpToPx(50)));

        places.add(place);

    }
}

private int dpToPx(int dp)
{
    return (int) (dp * Resources.getSystem().getDisplayMetrics().density);
}

Can converting from dp to px cause problems in some big or small screens? — neo, Jul 25 '17 at 15:32
Too big or small buttons or not showing some parts of buttons in screen. — neo, Jul 25 '17 at 15:35
It can of course if you set too big values to buttons. It depends on your requirements and how you use them. — Ayaz Alifov, Jul 25 '17 at 15:39

score 1 · Answer 2 · answered Jul 25 '17 at 15:23

I think it is because you change the id of the button, on the next iteration you get a null pointer exception. I'd say create button views programmatically entirely, not from an xml and then append those to the parent view. Or look into something like listviews.

I'd say go with your earlier approach and refer to this question for converting to DP.

How to inflate Button to LinearLayout progmatically in this case?

2 Answers2