android developers - what do you need from the designer?

i am NOT an android developer and im trying to understand what they need in terms of graphical resources to make an app that functions across many android devices.

i have (tried to) read this page http://developer.android.com/guide/practices/screens_support.html , but find it somewhat bewildering. they talk as if screen density is the important thing "Supply alternative bitmap drawables for different screen densities" but then, if you dont know the size of the screen, you cant really think in terms of layout. is the idea to make buttons and logos that are the same size on all screens with the same density, such that on a large screen there is just a bunch of space, and on the small screen its all packed in tight? i dont understand how just thinking in pixel density gets me any closer to knowing what to provide.

are you supposed to create resources for every screen size AND pixel density? say it aint so.

anyway can somebody tell me... if you were developing an app what do you need for graphics? is it possible to provide graphics that are large and just let them scale down? is it inevitable that the devloper will have to mess with the graphics himself anyway? or can he be provided with sets of png files of certain sizes that wi开发者_Go百科ll be ready to use?

thanks!

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Here's what we do at my work place. Suppose we get a desing for the app. We make our designer create 3 psds versions for the same desing. the 3 psd's are for the 3 ranges of desnity. The size used for the psd are

240*320 (Low Density)

320*480 (Medium Density)

480*800 (High Density)

Most of the time when I write layouts, I use wrap_content which means a view must take the size of the content it wraps. Which works most of the time as I have a density specific version of the design so the image i use as background should be suitable. The thing to note is that, in android you can can put the 3 sizes of the same image in different folders such as drawable/ldpi, drawable/hdpi.

Eg: you have a bg.png and have a version for large phones and a version for small phones. You put the big bg.png into hdpi folder and the small png in the ldpi folder. Android will automatically select the appropriate image based on the phone density. But you need to make sure the file name is the same.

There are cases where you need to resize you background images without makeing the image looking too scaled. For this android uses the draw9patch tool. With this tool you can specify areas which can scale and areas that shouldn't scale.

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9 Patch png's are your friend. Read up on them here:

http://developer.android.com/guide/topics/resources/drawable-resource.html#NinePatch

and here:

http://developer.android.com/guide/developing/tools/draw9patch.html

Those are your best bet for any kind of graphic that will stretch nicely (i.e. not gradients, they will come out slightly pixelated on some screens probably) The power of these types of images is that you can tell the system which pixels to repeat if it needs to stretch the graphic. This means that stretching can be done without loss of image quality (again depending on your image and how you choose to make the nine patch. The "show bad patches" button in the draw9patch program will show you potential problems. Hint: keep your repeatable pixels down to 1 on left and 1 on top and you'll have no problems with bad patches) Any graphics that can be made in to 9 patches will only need 1 size since the system can effectively make it whatever size it needs.

are you supposed to create resources for every screen size AND pixel density?

You may if you like. This would ensure that the application will look great across all devices. I understand that this is not feasible for all projects though. In general if you make separate resources for the different densities you'll get something that looks acceptable on most of the devices out there. All of the devices are classified as ldpi, mdpi, or hdpi (there may be an "extra high" level now too, I am not certain off the top of my head) So if you supply graphics for those 3 densities then the system will know where the device falls under and will pull the correct graphics.

is it possible to provide graphics that are large and just let them scale down?

Yes the system will scale down your graphics if needbe. But be aware there are consequences with this approach. First every time the system hast to scale a graphic up or down it is going to taking up CPU and memory to do so. This may not be an issue if you have relatively few things to scale, but if you have many it could cause noticeable lag time during on the lower power phones. Second, To my knowledge all of the graphics in android are raster, which means if you are letting the system scale something up or down image quality is going to decrease some. Again depending on the specific images this may be more or less noticeable on the actually device at runtime.

My best advice is supply them with resources of a few different sizes and run the app on as many different devices as you can. Once you see how your different resources look on the devices of different sizes you'll have a much better feel for which ones you need to supply to get the UI looking as consistent as possible across the largest swath of screen sizes and densities.