Develop Reference

Incorrect image size on different screen size

I have a screen on which I need to display a number of images inside a horizontal LinearLayout.
I designed it for an xhdpi. I set the sizes of each ImageView to 100dp, and on an emulator (xhdpi 768x1280 4.7" screen) it looks something like
this while on a tablet emulator (xhdpi 1534x2048 9" screen) it looks like this.
In the latter, the images aren't scaled properly to look like it does on the smaller screen.
Is there a way to make it look the same on both screen sizes?

to make your layout adjust on different screen you need to design it to be responsive. Yes like what G.Dator said, you can use weight attribute. Here's the example :
<LinearLayout
android:layout_height="200dp"
android:layout_width="match_parent"
android:orientation="horizontal">
<ImageView
android:layout_width="0dp"
android:layout_height="200dp"
android:layout_weight="25"/>
<ImageView
android:layout_width="0dp"
android:layout_height="200dp"
android:layout_weight="25"/>
<ImageView
android:layout_width="0dp"
android:layout_height="200dp"
android:layout_weight="25"/>
<ImageView
android:layout_width="0dp"
android:layout_height="200dp"
android:layout_weight="25"/>
</LinearLayout>
Please let me know if you have further question.

Actually, the image is the same size in 2 devices. The problem is the difference between your dp width of your phone (384dp) and your tablet (767dp). There're few ways to resolve it:
using multiple layout files for sw360 and sw720. You can check this Google Guide
Using the same weight for all your ImageView with adjustViewBound=true to keep your image ratios.
Using code to set your ImageView size programmatically.

In addition to implementing a responsive layout structure (like what #Bhimbim mentioned), there is a library (https://github.com/intuit/sdp) which can be useful when you want to code once and use it on multiple different devices, it offers you sdp unit instead of dp which helps your view to scale better.
Example:
layout_width="#dimen/_30sdp"
layout_height="#dimen/_30sdp"
(Sorry i couldn't comment as i have registered recently).

Set Width And Height For Phone And Tablet

i am developing webview android app for phone and tablet, and i am using tablelayout, this is my front page
i want to set width and height that will fit to screen when comes to tablet or big screen, how can i ? this is my xml
<TableRow
android:id="#+id/tableRow1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
>
<Button
android:id="#+id/button"
android:layout_weight=".50"
android:layout_height="150dp"
android:background="#drawable/hindi"
/>
<Button
android:id="#+id/button1"
android:layout_weight=".50"
android:layout_height="150dp"
android:background="#drawable/punjabi"
/>
</TableRow>

Do you mean you want different layouts that will fill the screen for tablets and other big screens?
Example:
tablets = 1 row has 3 buttons
big screens = 1 row has 5 buttons
I think the best way to do this is to create different XML layouts for each screen size. You can have 1 layout for phones (ex. 2 buttons per row) and 1 layout for tablets (ex. 3-4 buttons per row). You can then adjust the layout separately. I suggest you read the How to Support Multiple Screens section of the Android developer docs for more info, since I can't see you're entire XML.
Also, if you're table and TableRow fills-up the entire width of the screen, I suggest using match_parent instead of wrap_content.

Too much padding around Button's Text

I have a fragment that takes up the whole screen, with Buttons and a SeekBar which scale to fit it, as well as fixed size TextViews. I use linear horizontal and vertical layouts with weights to achieve this.
The problem is I can't get the button text large enough without it making the buttons expand in size. For some reason, any text size greater than about 35sp makes the button expand, no matter how big the button is. This screen shot shows the button sizes have plenty of space for the text:
Ideally I would like the "<" and ">" characters to fill the buttons. (I was going to programmatically change the font size according to the button size, e.g. for different screen sizes) but haven't tried since I can't even get the static layout to work.
Edit: I would like to avoid images, since if I had 15 buttons, and 8 buckets, that would be 120 images I need!
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/VerticalLinearLayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:paddingBottom="0dp"
android:paddingLeft="0dp"
android:paddingRight="0dp"
android:paddingTop="0dp" >
<!-- ........ -->
<TextView
android:id="#+id/trackTextView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge" />
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="2" >
<Button
android:id="#+id/trackPreviousButton"
style="android:buttonBarStyle"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
android:text="#string/button_track_previous"
android:textSize="35sp" />
<Button
android:id="#+id/trackNextButton"
style="android:buttonBarStyle"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
android:text="#string/button_track_next"
android:textSize="35sp" />
</LinearLayout>
<SeekBar
android:id="#+id/seekBar"
style="#style/tallerBarStyle"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1" />
<!-- ........ -->
</LinearLayout>
I have tried adding the following line to Buttons, but it only makes a small difference, if any:
android:padding="0dp"
Advice on getting the font height to fill the buttons without padding is my primary question. (But if the problem of dynamically sizing the text to fill the buttons for different screen sizes can be solved at the same time, that would be brilliant).
Edit: it turns out that using larger font sizes affects the effect of weighting for the height of the linear layouts, which is why there seemed to be padding - larger font size increased the button size, not because of the padding (which was 0) but because of the weighting

Button is not the right widget for your purpose. Use an ImageButton (or even an ImageView) instead.
I was going to programmatically change the font size according to the button size, e.g. for different screen sizes
Your current approach will land you in a lot of problems regarding proper sizing of your UI components. Given the plethora of android devices out there, screen size is just one aspect of the problem. You will also be dealing with varying screen densities. Best approach would be to put size/density buckets (drawable-mdpi/hdpi/xhdpi) to use. Help android in working for you.
Use drawables to indicate next and previous. If you're worried about the drawables being too small for tablet screens, create appropriate drawable resources/folders:
// Phones - 4 to 7 in
drawable-ldpi
drawable-mdpi
drawable-hdpi
drawable-xhdpi
drawable-xxhdpi
// Tablets - 7 to 10 in
drawable-large-mdpi
drawable-large-hdpi
// Tablets - 10 in
drawable-xlarge-mdpi
This list may not be exhaustive. Consider doing some research before finalizing your size/density buckets.
Output:
# drawable size 32dp:
# drawable size 64dp
Now it becomes quite straightforward - finalize drawable size by visual inspection on a phone, on a 7 inch tablet, and on a 10 inch tablet. Then use density scales to create and store appropriately sized drawable in the folders I mentioned above. Let android deal with what bucket to pick from.

The problem is by default buttons include a minHeight attribute. I had the same problem and solved it with just a single line of code in my XML file:
android:minHeight="0dp"

There is a quick and easy solution to your problem!
Auto-sizing text in Android is fiendishly difficult in my experience, especially when padding is involved. I would advise that instead of using an angle bracket character, you use a drawable - there are plenty of arrow icons available online - and an ImageButton. For example:
<ImageButton
android:id="#+id/trackNextButton"
style="android:buttonBarStyle"
android:layout_width="0dp"
android:layout_height="match_parent"
android:layout_weight="1"
android:src="#drawable/left_arrow"
android:scaleType="fitXY"
android:padding="0dp"
android:textSize="35sp" />
By using different ScaleTypes you can alter the stretching of the image. Even better, the screen sizes problem is solved because you can add different drawables for different densities.

Use minWidth="0" or "1" to reduce the horizontal padding on a text Button.

Single Layout for all screen sizes

I have read many documentation on supporting multiple screen sizes but still confused.
I have read like if specified in dp it will get automatically scaled.
In my sample i just have a single layout. there i have placed an edit text.
and given width , suppose 170 dp. suppose width wise it is half the screen in a 5 inch phone emulator.
What i was expecting is, if i show it on an tablet 7inch or 10 inch , there also it will be half the width of the screen (i.e it will get automatically scaled). But it didnt. in a 10 inch tablet it is only very small size.
what should i do to achieve this only through layout xml ( only single xml )

Dont set a Static width for the Textview as android will automatically scale it the the correct size using
android:layout_width="fill_parent"
android:layout_height="wrap_content"
Basically what this does is makes the TextView the full size of the width of the device, and wraps the Height only to the needed height of the text.
YOu could also do warp_content for width to if you wanted. This is the best way. If you set it statically, you will need to create different layouts using XML.

Learn to use layout weights, you can use them like a percentage of 100.
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal" >
<TextView
android:layout_width="0dip"
android:layout_height="wrap_content"
android:layout_weight="50"
android:text="aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa" />
<View
android:layout_width="0dip"
android:layout_height="0dip"
android:layout_weight="50" />
</LinearLayout>
Here the textview takes up 50% of the screen width and the other view is a kind of invisible spacer taking up the other 50% of the screen width.
Which looks something like this (Eclipse XML preview):
As you can see the textview wraps when it gets to 50% of the screen. Working on all sizes of screen.

Android, images and dpi

I am using WVGA800 skin in Android emulator, so the density (hw.lcd.density) is 240. I have to put 4 image buttons (72 pixels per inch) at the bottom of activities view. As the resolution is 480X800, I asummed that the width of image must be 120 pixels. The problem is when application is launched, the 3 buttons take all width and there is no place for 4th button... Then I created button image in Fireworks with resolution 240 pixels per inch and in 120px width, but problem remains. Could somebody explain how to make correct drawables (sizes and dpi) so that they can be displayed pixel in pixel on Android?

If you put your images in res/drawable, Android assumes they're for 160dpi and scales them accordingly for different resolutions.
Your options are either to put the button images into res/drawable-hdpi signaling that they're intended for densities around 240dpi, or into res/drawable-nodpi to make them never scale regardless of the current screen density.
You still reference them as #drawable/whatever in layouts, the engine picks the best match automatically.

Disregard the image DPI entirely. It's irrelevant, all you need to know is the pixel size. What I would actually suggest is to create a NinePatch image to use as your button background. You'll actually need a few to put into a StateListDrawable, as this is how the different focus states are defined (e.g. Pressed, Focused). Once you have your NinePatch, just create a LinearLayout like so:
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
>
<Button
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:background="#drawable/my_nine_patch"
android:text="button 1"
android:layout_weight="1"
/>
<Button
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:background="#drawable/my_nine_patch"
android:text="button 2"
android:layout_weight="1"
/>
<Button
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:background="#drawable/my_nine_patch"
android:text="button 3"
android:layout_weight="1"
/>
<Button
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:background="#drawable/my_nine_patch"
android:text="button 4"
android:layout_weight="1"
/>
</LinearLayout>
Set all the buttons to fill_parent and give them all an equal weight. They'll stretch to fit evenly to the parent, and you don't have to worry at all about specifying a constant pixel or dip size. Also, it'll evenly split onto any Android device, no matter the resolution.

The width is actually 320 pixels, so for 4 buttons across the entire screen set each to 80dip. Android will then adjust your density independent pixels to the proper screen size of 480 pixels.