Android – How to Convert ‘dp’ to ‘px’?

androiduser-interface

I am reading this article: http://developer.android.com/guide/practices/screens_support.html

It says that the formula Android uses to convert between a dp unit to a px unit is the following:

    px = dp * (dpi / 160)

The article also gives an example when the dpi is 240, which gives us px = 1.5 (I'm calculating for one single dp pixel)

However, what exactly does 1.5 mean here? Once the px units are actually the physical device pixels, will Android draw 1 or 2 pixels?

Best Answer

It depends on the context.

If the dp value is used in a context that implies size, like the android:layout_width attribute, the logic described for Resources.getDimensionPixelSize() will be used. That is, the px value will be rounded to the nearest integer value, with the special case that if px > 0, then the actual value will be at least 1.

If the dp value is used in a context that implies offset, like the android:insetLeft attribute of the Inset Drawable, the logic described for Resources.getDimensionPixelOffset() will be used. That is, the px value will simply be truncated to an integer value.

Sometimes the unmodified floating point value is used, such as for the android:dashWidth attribute of the <stroke/> tag in a Shape Drawable, but this is pretty rare. Usually either the size or the offset logic is used, even if the floating point value could be used.

Related Solutions

Android DP to PX Conversion – Convert DP, PX, SP

DP to PX:

public static int dpToPx(float dp, Context context) {
    return (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dp, context.getResources().getDisplayMetrics());
}

SP to PX:

public static int spToPx(float sp, Context context) {
    return (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, sp, context.getResources().getDisplayMetrics());
}

DP to SP:

public static int dpToSp(float dp, Context context) {
    return (int) (dpToPx(dp, context) / context.getResources().getDisplayMetrics().scaledDensity);
}

Xamarin.Android – How to Convert dp to px

Solution to "First code":

Xamarin tends to move constants into their own enums. COMPLEX_UNIT_DIP can be found on ComplexUnitType enum. Also you cannot have < HEIGHT > in your code you actually need to pass in dips to get the equivalent pixel value. in the example below I am getting pixels in 100 dips.

var dp = 100;
int pixel = (int)TypedValue.ApplyDimension(ComplexUnitType.Dip, dp, Context.Resources.DisplayMetrics);

Solution to "Second code":

You need to explicitly cast 'DisplayMetrics.DensityDefault' to a float and the entire round to an int:

int pixel = (int)System.Math.Round(dp * (displayMetrics.Xdpi / (float)DisplayMetrics.DensityDefault));

I prefer the first approach as the second code is specifically for calculating along the "x dimension": Per Android docs and Xamarin.Android docs, the Xdpi property is

"The exact physical pixels per inch of the screen in the X dimension."

Best Answer

Related Solutions

Android DP to PX Conversion – Convert DP, PX, SP

Xamarin.Android – How to Convert dp to px

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