Question

I want to calculate how much views are displayed on screen at a time if view width is fixed. For that I get one Layout add some views in it with fixed size and run it.

But as per my calculation I get wrong number of child to displayed on screen as it shows on screen.

Please tell me where I am wrong?

Here is my code…

   In Activity ...
    ----
     LinearLayout featured_listlayout_horizontallayout=(LinearLayout)findViewById(R.id.featured_listlayout_horizontallayout);
            LayoutInflater inflater=LayoutInflater.from(getApplicationContext());
            for(int i=0;i<20;i++){
                LinearLayout childItem=(LinearLayout)inflater.inflate(R.layout.childitemlayout,null);
                Button btn=(Button)childItem.findViewById(R.id.btn);
                btn.setText("Item"+(i+1));
                featured_listlayout_horizontallayout.addView(childItem);
            }

    DisplayMetrics dm = new DisplayMetrics();
    getWindowManager().getDefaultDisplay().getMetrics(dm);

    final int height = dm.heightPixels;
    float screenWidth = dm.widthPixels;//Screen Width in pixel

    float itemWidth=getResources().getDimension(R.dimen.featured_text);//itemWidth in DP
    itemWidth=convertDpToPixel(itemWidth, getApplicationContext());// convert itemWidth into pixel

    System.out.println("screenWidth "+screenWidth+" itemWidth "+itemWidth);

    float noOfItem=screenWidth/itemWidth;
    System.out.println("noOfItem "+noOfItem);

    -----

    convertPixelsToDp method:


    public float convertPixelsToDp(float px,Context context){
            Resources resources = context.getResources();
            DisplayMetrics metrics = resources.getDisplayMetrics();
            float dp = px / (metrics.densityDpi / 160f);
            return dp;
        }  

  convertDpToPixel method:

   public float convertDpToPixel(float dp,Context context){
        Resources resources = context.getResources();
        DisplayMetrics metrics = resources.getDisplayMetrics();
        float px = dp * (metrics.densityDpi/160f);
        return px;
    }

    activity_main.xml

    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity" >

        <HorizontalScrollView
            android:layout_width="match_parent"
            android:layout_height="wrap_content" >

            <LinearLayout
                android:id="@+id/featured_listlayout_horizontallayout"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:paddingBottom="5dp" >
            </LinearLayout>
        </HorizontalScrollView>

    </RelativeLayout>


    childitemlayout.xml

    <?xml version="1.0" encoding="utf-8"?>
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="@dimen/featured_text"
        android:layout_height="@dimen/featured_image"
        android:orientation="vertical" 
        android:background="#0000ff">

        <Button android:id="@+id/btn"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:text="Button"
                android:background="#ff00ff"/>


    </LinearLayout>



    dimen.xml

    <?xml version="1.0" encoding="utf-8"?>
    <resources>
             <dimen name="featured_text">80dp</dimen>
             <dimen name="featured_image">60dp</dimen>
    </resources>

Answer 1

But as per my calculation I get wrong number of child to displayed on
screen as it shows on screen.

You get the width of the screen in pixels:

float screenWidth = dm.widthPixels;

and for the width of the items you get the width in pixels but you also transform it into dp:

float itemWidth=getResources().getDimension(R.dimen.featured_text);
itemWidth=convertPixelsToDp(itemWidth, getApplicationContext());

And then you try to use those two values together.

Either use pixels or dp.

Edit 2:

You should really read about the inflate() methods of the LayoutInflater class. You need to inflate the views with the proper LayoutParams and this is done by providing the ViewGroup that will be the parent of the inflated layout file. So you need to do:

LinearLayout childItem = (LinearLayout) inflater.inflate(
                    R.layout.aaaaaaaaaaaa, featured_listlayout_horizontallayout, false);

If you don’t do this, your inflated views will not have the set size on them(as you have probably seen they will wrap their content). After you’ve done the modification above and you want to find out the number of children that wopuld be visible(completely or partially) before you actually add them in the layout(using the dimension you set in the xml layout) you just divide the screen width to the dimension from the resources:

int screenWidth = dm.widthPixels;
int itemWidth=getResources().getDimension(R.dimen.featured_text);
int noOfItem=screenWidth/itemWidth;
// if we have a remainder from the division it means there is extra space
// so we need to check if we have more items so there is another child partially showing
int rem = screenWidth % itemWidth;
if (rem != 0) {
    noOfItem += 1;
}

Edit 1:

Your current code will not work and you didn’t understand my answer. dm.widthPixels returns the screen width(which your HorizontalScrollView fills) in pixels. getResources().getDimension(R.dimen.featured_text) will return the value of that dimension resource in pixels. There is no need for methods to transform those values, just use them directly. Even so your code will not work right as you wanted because you don’t take care of assigning the proper LayoutParams to your views. You should inflate the child layout like this:

LinearLayout childItem = (LinearLayout) inflater.inflate(
                    R.layout.aaaaaaaaaaaa, featured_listlayout_horizontallayout, false);

Also, I would just use the code below(used in the onCreate method) to find out the visible children on the screen(completely visible or partial visible):

featured_listlayout_horizontallayout.post(new Runnable() {

        @Override
        public void run() {
            DisplayMetrics dm = new DisplayMetrics();
            getWindowManager().getDefaultDisplay().getMetrics(dm);
            // screen width
            final float screenWidth = dm.widthPixels;
            final int count = featured_listlayout_horizontallayout
                    .getChildCount();
            int realWidth = 0;
            int visibleChildren = 0;
            for (int i = 0; i < count; i++) {
                final View child = featured_listlayout_horizontallayout
                        .getChildAt(i);
                realWidth += child.getWidth();
                if (realWidth < screenWidth) {
                    visibleChildren++;
                } else {
                    visibleChildren++;
                    break;
                }
            }
            // visibleChildren now has the visible children on the screen
        }

    });