android px dp,Formula px to dp, dp to px android

In most of the cases, conversion functions are called frequently. We can optimize it by adding memoization. So,it does not calculate every-time the function is called.

Let's declare a HashMap which will store the calculated values.

private static Map pxCache = new HashMap<>();

A function which calculates pixel values :

public static float calculateDpToPixel(float dp, Context context) {

Resources resources = context.getResources();

DisplayMetrics metrics = resources.getDisplayMetrics();

float px = dp * (metrics.densityDpi / 160f);

return px;

}

A memoization function which returns the value from HashMap and maintains the record of previous values.

Memoization can be implemented in different ways in Java. For Java 7 :

public static float convertDpToPixel(float dp, final Context context) {

Float f = pxCache.get(dp);

if (f == null) {

synchronized (pxCache) {

f = calculateDpToPixel(dp, context);

pxCache.put(dp, f);

}

}

return f;

}

Java 8 supports Lambda function :

public static float convertDpToPixel(float dp, final Context context) {

pxCache.computeIfAbsent(dp, y ->calculateDpToPixel(dp,context));

}

Thanks.