Relation between dp and android different screen size

Question

I want to make folders of dimens according to screen size and not according to density so what will be the dp values for each screen size. I want to adjust my DP value according to screen size only and not according to density so is there any formula for calculating dp for different screen size . As there is a relation between density , pixel and dp . But i want it for different screen size . It is like for normal-xhdpi screen and for normal-xxhdpi screen the size of the button should be same as independent of density as name suggest of "DP"

Answer 1

Create three different Layouts Folder in your res folder for all devices and use the dimensions accordingly.

Generic Layout Folders

res/layout-small
res/layout-normal
res/layout-large
res/layout-xlarge

After you are done with making your Normal/Medium Layouts follow these steps:

1. Convert the Normal Dimensions for other Screen Sizes.
2. Copy your Normal Layout xml files in to other Folders.
3. Change the suffix of the dimensions used according to the folder that you are in
4. Resize the Image Resources in your drawable folder (Width and Height - Same technique as we used for converting the dimens) and put them in their respective drawable folder (drawable-ldpi, drawable-mdpi, drawable-hdpi, drawable-xdpi and so on).
5. Then your Layouts should work on every device with correct positioning.

For converting Values

0.75 - ldpi  (small)   //mdpi dimens *0.75
1.0  - mdpi  (normal)  //First create these dimensions
1.5  - hdpi  (large)   //mdpi dimens *1.5
2.0  - xhdpi (xLarge)  //mdpi dimens *2.0

For Example

android:layout_width="66dip" //in normal
android:layout_width="100dip"//in large 66*1.5=100(approx)
android:layout_width="52dip" //in small 66*0.75=52(approx)

Also new Qualifier has been introduced - SmallestWidth - AvailableScreenWidth - AvailableScreenHeight

read more about it here https://developer.android.com/guide/practices/screens_support.html

If you are looking in Java code

 /// convert dp to pixels
   public static int dp2px(Context context, float dp) {
      return Math.round(dp * context.getResources().getDisplayMetrics().density);
   }

I hope this helps.

Answer 2

public static float dpToPx(Resources rs,float dp){
        DisplayMetrics metrics = rs.getDisplayMetrics();
        float px = dp * (metrics.densityDpi/160f);
        return px;
    }

public static float pxToDp(Resources rs,float px){ 
        DisplayMetrics metrics = rs.getDisplayMetrics();
        float dp = px / (metrics.densityDpi / 160f);
        return dp;

    }