Android same screen size with different density
<p>I've read a lot about screen sizes and densities in android .. <br/>
But seems like I'm missing something about it .. <br/>
I've designed my layouts using HVGA emulator skin .. When I tried different screen sizes for HVGA ( 2 to 10 inches ) it just worked fine .. but when I tried using different skin with different density like ( WVGA800 )  it didn't appear like expected .. <br/>
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So when I test my app against (WVGA800 skin )( 4 inch screen size ) there is a white space below the layout (it doesn't fill the whole screen ) but it works fine for (HVGA skin )( 4 inch screen size ) although both of the skins are classified as (normal screen ) but with different densities .. 
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Any ideas why this happened or what is the difference between ( 4inch HVGA ) and (4inch WVGA800 ) !! although they both are described as (normal screen size ) .. <br/>
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Note : I know about (dp - fill parent ..... ) and all these stuff but it seems it doesn't work well for me ..
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