Question

I use a button with an image as its background, this image has a size of 30×29, but it’s resized and enlarged x2 (I think). Here is the XML code of my button :

<Button
        android:id="@+id/buttonBack"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="12dp"
        android:layout_marginTop="10dp"
        android:background="@drawable/bouton_back"
        android:maxHeight="30dp"
        android:maxWidth="30dp" />

And in Java :

backButton = (Button) findViewById(R.id.buttonBack);

What is wrong with that ? I do the same with other buttons and there is no problem… thank you.

Answer 1

Are you supplying bouton_back in your resources using multiple densities? Using dp units to size your button isn’t sufficient; you must also provide multiple sizes of your images:

• ldpi: 120dpi
• mdpi: 160dpi
• hdpi: 240dpi
• xhdpi: 320dpi

The conversion formula is as follows:

px = dp * (dpi / 160)

Where px is the final image size in pixels, dp is the desired size in density-independent units, and dpi is the target density.

Simplifying this formula, using the size in pixels of your mdpi images as the baseline:

ldpi = mdpi * 0.75
hdpi = mdpi * 1.5
xhdpi = mdpi * 2.0

Going back to your sample code, if you want a button that is 30dp by 30dp, you should be providing images for each density:

• ldpi: 23px x 23px
• mdpi: 30px x 30px
• hdpi: 45px x 45px
• xhdpi: 60px x 60px