Develop Reference

Android : set width and height of bitmap base on screen size programmatically

let say I have Bitmap A with the dimensions 165x15.7 which is displayed correctly on 320x240 screen size with 0.75 density. if i want to show the bitmap images on different screen size like 480x320 with 1.0 density, how to set the bitmap width and height dynamically on different screen size? i want to do it programmatically,I don't want to use xml/ multiple layouts/ multiple dimensions.
any help would be appreciated. thank you.
here is for the example
320x240 screen dimension
480x320 screen dimension
as you can see the screenshot above, the example logo look smaller on 480x320 screen dimension

You can get the scale factor of device screen to scale the image size with this code :
getResources().getDisplayMetrics().density;
This will give you:
ldpi = 0.75
mdpi = 1.0
hdpi = 1.5
xhdpi = 2.0
xxhdpi = 3.0
xxxhdpi = 4.0
source : https://stackoverflow.com/a/10948031/6217595

If I have an image 50dp wide/tall in xhdpi, what size do I make for mdpi?

I am working with a graphic designer at the moment who is trying to verify what sizes images I am currently using in my app so he can create new images in the right size for all resolution modes (designing the image at the smallest size and then scaling it for the other modes).
In my app, I am emulating a device that is 720 x 1280: xhdpi, and on this device, an ImageView is set to size 50dp x 50 dp.
Is it correct to say 50 dp xhdpi -> 25 dp mdpi? 100px? Or 50px? What exactly? What is the correct size that we should be making for the smallest size?

According to Android Documentation.
From a base image size, there is a 3:4:6:8:12:16 scaling ratio in drawable size by DPI.
LDPI - 0.75x
MDPI - Original size // means 1.0x here
HDPI - 1.5x
XHDPI - 2.0x
XXHDPI - 3x
XXXHDPI - 4.0x
According to the upper difference you can calculate the ImageSize resoultion.
Update :
you have create different size of Image like HDPI, MDPI, XHDPI. but that is not mean that you can set ImageView Height and Width according to it's Drawable.
Example :
let's some device have small screenSize but it is high density support so you have to set high resolution density Image but the Size of the ImageView you have create small in that case.

Resolution 768 x 1280

Is it possible to make a layout for this nexus 4 resolution . my app give problem with custom views.
i have
layout-hdpi
layout-xhdpi
layout-xxhdpi
i know xhdpi includes 768 x 1280 and 720 x 1280 .

dpi only partially depends on resolution. It is a measure of how tightly the pixels are packed on the screen. Thus, it is a function of both resolution, as well as the physical size of the screen.
Saying 768 x 1280 px = xhdpi may be correct for some devices, but incorrect for others. For example, what if you have a 10 inch screen that has that resolution? That would most likely be ldpi.
In order to support multiple screens, please follow this guide: http://developer.android.com/guide/practices/screens_support.html
You may want to use dp's instead of pixels in your layouts for setting widths and heights. You can then customize layouts based on the current width of the device by using layout directories such as layout-sw320dp ("smallest width 320 dp").

Best quality image allocation from resources based on resolution/density

I'm struggling with a pretty trivial task in the Android "multiple-screen sizes" domain.
What I'm trying to achieve
A layout matching the screen width, with a nine-patch background which resizes (only horizontally, since there is always enough vertical space). Here is a dummy image:
My goal is, depending on the screen resolution, to display the image at the highest resolution possible, by using a set of different sizes, eg. 320x45, 480x67, 600x87, 720x101, without any down-scaling. I'm hoping for a non-programmatic solution.
An example with the above mentioned image sizes would be:
3.7" Nexus One (480 x 800) - the 480x67 image would look best.
4.7" Galaxy Nexus (720 x 1280) - the 720x101 image.
4.7" Nexus 4 (768 x 1280) - again the 720x101 image, stretching to the full 768 px width and becoming 768x101.
Issue
The whole Android resource allocation revolves around dps (density-independent pixels), when in fact I want to display an image based on the actual available pixels.
If I allocate the 480x67 image to res/drawable-mdpi and a 600x87 to res/drawable-hdpi, then image would display correctly on a 5.4" display of 480x800, i.e. mdpi display. However, a 4" 480x800 displays qualifies as hdpi and the system would appoint the 600x87 image, which won't fit the screen.
I tried the smallestWidth parameter as described in the online guide, but that yields strange results. For instance, a 3.7" 480 x 800 display (hdpi) uses my drawable-sw320dp image, although there is a drawable-sw480dp resource available too.
What is the best way to assign a stretchable, width-matching image with the best possible quality? Isn't there any non-programmatic solution?
Thanks in advance!

I believe that by combining density and screen size resource qualifiers you can achieve a close to optimal behavior.
Lets assume this kind of resource folders structure:
drawable-normal-hdpi - A normal size dictates minimum width of
320dp. hdpi dictates 1.5X dp to pixel multiplier. So the minimum px
width of the normal hdpi bucket is 480px. We put here a 480px wide
image.
drawable-normal-xhdpi - Again size dictates 320dp but this time
with 2X multiplier. So we use a 640px wide image.
drawable-xlarge-mdpi - Size means at least 720dp. mdpi multiplier
is 1X, so we use a 720px wide image.
Now lets look at some devices to see how they fall in with those buckets:
Nexus one - normal hdpi. Actual px width: 480px. The image fits
perfectly.
Galaxy nexus - normal xhdpi. We could fit a 720px image, so the
640px image we use isn't optimal - but it's very close.
Nexus 4 is just like the Gnex.
Nexus 10.1 (1280X800) - xlarge mdpi. We could fit 800px, our image
is 720px. Again not ideal but close enough.
Worst case scenario: image used could have 5-10% better quality.
Best case: perfect fit.
The main down side of this method is that you need to provide a lot of resources and folders to account for all the permutations of sizes and densities (even worse if you need to combine that with more qualifiers for locale, orientation and so on). However, as far as my Android understanding goes I don't think you can achieve something better than this without coding.
A remark regarding smallestWidth: Your example for the weird behavior is actually the expected behavior.
hdpi multiplier is 1.5 - So a 480px wide hdpi display is exactly 320dp wide. This makes the drawable-sw320dp the right choice, as documented. I'm not sure if you can combine the smallestWidth qualifier with the dpi qualifier. If it's possible you might get more accurate results than just size modifiers. But this would mean a lot more permutations for a 5% increase in image quality. Probably not worth it.

Actually, your method is not how it is supposed to be. I will suggest 2 ways for you, one is easy but doing programmatically, other one is using a custom view.
Method 1 - Programmatically
DisplayMetrics displaymetrics = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(displaymetrics);
int screenWidth = displaymetrics.widthPixels;
// this will determine "scale ratio" so using which image height and width won't matter
int imageOriginalHeight = 101; // your original image height
int imageOriginalWidth = 720; // your original image width
int imageScaleHeight = (screenWidth*imageOriginalHeight) / imageOriginalWidth;
LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(screenWidth, imageScaleHeight);
imageView.setLayoutParams(params);
imageView.setImageResource(R.drawable.file);
Method 2 - Custom View
You can use a custom view called ScaleImageView which is written by Maurycy Wojtowicz.
Class is defined like below:
This view will auto determine the width or height by determining if
the height or width is set(exact size or match_parent) and scale the
other dimension depending on the images dimension This view also
contains an ImageChangeListener which calls changed(boolean isEmpty)
once a change has been made to the ImageView
Here is how you are going to implement it.
Create a class named ScaleImageView.java and copy contents of the link above.
In your xml file, create a ScaleImageView, just same like ImageView (the example I am writing below is for filling screenwidth, and scaling height according to that so there will be no empty spaces on right/left)
<com.project.customview.ScaleImageView
android:id="#+id/scaleImageView"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:adjustViewBounds="true"
android:scaleType="fitCenter"
android:src="#drawable/file" />
If you need to declare and set programmatically in your Activity, it is also the same as using ImageView:
imageView = (ScaleImageView)findViewById(R.id.scaleImageView);
imageView.setImageResource(R.drawable.file);

In android you have the option hdpi, mdpi, xdpi,etc..
folders for that , you have to create different images according your device resolution and put your images at there after confirming your device resolution and density category.
for the more reference why it'll happen you can see here
here i explain some chart may be helpful to you.
Low density Small screens QVGA 240x320 (120dpi):
drawable-small-ldpi (240x320)
drawable-small-land-ldpi (320x240)
Low density Normal screens WVGA400 240x400 (x432) (120dpi):
drawable-ldpi (240 x 400 )
drawable-land-ldpi (400 x 240 )
Medium density Normal screens HVGA 320x480 (160dpi):
drawable-mdpi (320 x 480 )
drawable-land-mdpi (480 x 320 )
Medium density Large screens HVGA 320x480 (160dpi):
drawable-large-mdpi (320 x 480 )
drawable-large-land-mdpi (480 x 320)
Galaxy Tab ( 240 dpi ):
drawable-large (600 x 1024)
drawable-large-land (1024 x 600)
High density Normal screens WVGA800 480x800 (x854) (240 dpi):
drawable-hdpi (480 x 800)
drawable-land-hdpi (800 x 480)
Xoom (medium density large but 1280x800 res) (160 dpi):
drawable-xlarge (800 x 1280)
drawable-xlarge-land (1280 x 800)

How should i know the phone that has the specified arguments is the hdpi or ldpi

As the titles,the following is some arguments of the psd of my phone:
The width pixels:
The height pixels:
The width of document is:13.333 inch
The height of document is :7.5 inch
so the dpi will be 96,and we will know the phone is just a ldpi phone as the http://developer.android.com/guide/practices/screens_support.html
can anyone tell me whether it is right or not.

If your graphics are designed to display at 96 pixels/inch, then they are not a good match for Android. The minimum density devices are nominally 120 pixels/inch (called LDPI). If you put your graphics in res/drawable-ldpi, they will appear about 96/120 (or about 3/4) their original size (in inches).
If the images are displayed on a higher density device, Android will automatically scale the images up, so they will keep this size ratio regardless of actual device pixel density.
The only way to fix this is to rescale your images before adding them to yuor project. You will get the best quality if you rescale to each of the nominal pixel densities (120, 160, 240, and 320; you could also throw in 213 for tvdpi screens).