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How to update content of the activity without creating new Activity?

I'm trying to make an app and I have made a blueprint for a specific activity, but I don't know how to implement it. The layout contains few buttons at the top of the activity, and each button features some information, which is displayed inside the view. The view which needs to be updated is present under the buttons. I don't want the activity to be changed, instead it should update the contents of the View, which is different for each category/button.
By doing some research I have realised that the "Tab Layout" can be used to achieve my requirements, but I don't want the tabs and I need some stylish buttons as a replacement.
I know I'm not the best at describing, so I have looked upon Dribble and found one design which is 100% similar to blueprint.
I want to achieve this using XML and Java using Android Studio! Every suggestion will be a great support foy my app.
Thanks a lot.

As far as I know, you could achieve that by using fragments (which is the same concept you would have used on TabLayout). I don't really know how much knowleadge you have on Android, but if you know what a Fragment is, it should be easy for you to recreate the idea.
You have 3 buttons for 3 different fragments, so you must design every fragment by separate and change it depending the button you click.

How to change layout on button click in android app?

I am new in Android so correct me if i am wrong. When another activity is opened, the first one is destroyed. So i have to pass all variables to the new activty if i don't want to lose the data. Or, can I run another not UI thread that manages my data?
Basically I need to change layout in my app on button click. Is there any way to do it within the same activity or i have to start another activity with the new layout?

You can use one activity in your app and do what you want in fragments. Navigation is good tool to use for relating fragments to each other.

well initially you can use a single activity and in that activity you can call multiple fragments as per your need,
and for the data you can use MVVM architecture with room architecture, it saves your lots of time and code.
and go with navigation graph if you want a quick and easy implementation.
you can start all this with this demo.

How to change app theme from ordinary "Blank Activity" to "Master/Detail Flow"

I have an application that works on the basic theme "Blank Activity" and what i would like to do is to change it to a "Master/Detail Flow" theme. I do know that this will make my application work on android SDK 11 + (android 3.0 Honeycomb +), that is OK with me. The issue is i don't know where to start from, what are the basic steps to make this BIG conversion? I couldn't find any example to help me out with this issue. What should i be looking for. i am sure this has been done, can you at least please give me some pointer on how to do this?
my Application is not that complicated it uses activities, async tasks, DB, custom lists,... it is very basic. I use the custom list to display data and when i click on it it displays much more details, so I thought what better way to do this in a more professorial matter than the "Master/Detail Flow". If you have any tutorial regarding the "Master/Detail Flow" that you can hook me up with that might help.

I have an application that works on the basic theme "Blank Activity"
and what i would like to do is to change it to a Master/Detail Flow"
theme.
I think a change of the application flow would be more appropriate then a change of theme. Two obvious questions that would appear are why do you suddenly want to make this change and are sure your app makes sense in a master/detail flow? The answer would most likely be positive but you should answer them nonetheless.
I do know that this will make my application work on android SDK 11 +
(android 3.0 Honeycomb +), that is OK with me
I don't see why you're app couldn't run on versions below with the new master/detail stuff.
The issue is i don't know where to start from, what are the basic
steps to make this BIG conversion? I couldn't find any example to help
me out with this issue. What should i be looking for. i am sure this
has been done, can you at least please give me some pointer on how to
do this?
You haven't provided details about how is your app implemented. The change would revolve around fragments so a BIG question would be if the current single pane version is built using the fragments framework.
If your app is built using fragments then making the change shouldn't be too hard. You'd need to:
establish which parts(fragments) should be combined in an activity(from your old ones) to make the master/detail(when the space would allow it)
change the multi pane activity to accommodate the new fragment(s). This should be easy to do but it would depend on the size of the features exposed by each of those fragments.
modify the rest of the activities(for when the app will not run in the multi pane mode), this would be small changes as the activities would mainly remain as the current version
If your app isn't built using fragments, then what I said above still applies but you'd need to also actually make the required fragments wrapping whatever functionality your app has. This would most likely result in a big code refactoring.

Here is a tutorial about the Master/Detail template in Android - An Android Master/Detail Flow Tutorial.
As far as I understand your application is up and running - so I'm not sure whether it is worth it to try rewriting it, unless you are experiencing some problems of course. :)
In general the master/details flow requires the following steps:
Implement a ListFragment showing basic information of your items
Implement a Fragment showing detailed information about a particular item
Make an xml layout file for large devices (located in layout-sw600dp folder for example). In this layout you have to put both your fragments.
Write a general version of this layout file (i.e. file with the same name but located in the layout folder), which contains only the ListFragment.
Let your activity handle onItemClick event from the ListFragment. Each time an item is clicked, you have to check if the activity is showing both fragments or only the ListFragment. If both are visible, you have to notify the details fragment that new item is selected so it can show its data. Otherwise you have to create new details fragment (you reuse it of course), pass it some information about the selected item (so it can show the item's data) and replace the ListFragment with the new one.
That a basic overview, but it should be enough to give you some idea about this flow. If you need any more details - just let me know. :)

Master/detail flow and blank activity is not same as you want to change by only changing app theme or app base theme. It will be better, if you first design master/detail flow template using UI fragments, then according integrate you blank activity with the master template making necessary changes. And for master/detail flow tutorial just google it, you will find lots of example there.

Here are some links from developer.android.com fragment-ui and adaptui
These are some guidelines about fragments but they are told using a master/Detail app.
Also dont forget to checkout the news reader app provided as sample in the second link.

If you have a recent version of the Android SDK, you should be able to create a new Android application and during that process you can elect to have the wizard create a Master/Detail Flow app for you. It will create a basic working app so that you can look through the code and understand the necessary parts.
Then, depending on how simple your app is, you may want to move all your present code to the new application or vise versa.
Macro changes that will happen:
Change all your current Activities to extend Fragment instead.
You will have to create a FragmentActivity to call your Fragments. This will basically be the boilerplate code, with just the names of your Fragments added to it.
Don't forget to double check your Manifest!
In your converted Fragments that previously extended Activity:
Everywhere you needed a Context, switch that with getActivty() (or create a global variable so that it is only called once)
Change onCreate() to
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
mView = inflater.inflate(R.layout.fragment_signals, container, false);
setHasOptionsMenu(true); // Add if you want to display a Menu
// Your initiation code here
return mView;
}
If you have a menu, change it to
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
inflater.inflate(R.menu.activity_main, menu);
super.onCreateOptionsMenu(menu, inflater);
}
And that's it for basic applications. When you first change Activities to Fragments, there will be many errors. But, they are all easy to fix.

New to android fragments - looking for a few answers

I'm fairly new to android, and have been working on an app for a few weeks. I want the app to run on handhelds and tablets. I decided to implement fragments after running things on my tablet and am having trouble getting my head around it to get the ball rolling. My app is like most: The first page you see is a menu list of various activities you can navigate to, some of which call other activities. I've read countless tutorials, but still have a few questions, I'm hoping someone can help with. I haven't had any luck finding the answers on the internet.
1) Should the main menu be in a fragment or just remain an activity that calls fragments?
(I'm thinking it should be a fragment as well)
2) I've read that the activities are just a portal to the fragment, so in the main menu all of my logic should go in the fragment?
3) Why does eclipse throw a dummy class into the wizard setup? Shouldn't this package just be deleted and the array adapter or whatever be put into the logic of the main menu or do I require another class for a good reason?
4) I also read somewhere that the Main activity must be called Main.java is this true? I don't see why it would be.
I realize these are all probably pretty simple questions to someone that has a grasp on fragments, but I don't!
Thanks for any answers
Ken

1) Yes, if you are handling logic and ui, and you are attempting to do your best and want to have a structure that you can easily support multiple screen sizes, your menu should be a fragment.
I think the activity is the mechanism to handle what fragments to display.
So on a phone the first activity just displays the menu fragment and launches a new activity to handle the selection.
While on a tablet you might have the menu fragment on the left side of the screen and do a fragment transition for the right side of the screen upon user selection
2) Your activity still has work to do to coordinate those fragments as my example in 1.
3) You don't need that class
4) You can name anything at all, anything at all. Pay attention to what's specified in your manifest. Your app can even have multiple starting points / icons in the launcher if you specify it as such in the manifest.

1) If you want different layouts depending on device and/or orientation then yes. Maybe you want the main menu to be located in a pane on the left on a tablet while it's a full screen list on a phone.
2) This is a bit more tricky to answer. It all depends on how you design your application, and there really is not right or wrong here. You could opt for an MVC like approach where you put the actual logic in a controller. You could let your Activity deal with what happens when a menu item is selected. You could use an eventbus (Otto or Guava) to communicate between fragments. It's up to you.
3) Not needed
4) No, you don't have to name it Main.java. I think you may be confusing this with the public static void main(String[] args) entry point of a standard J2SE program?

View different images depending on what item in my list view I click

I'm fairly new to Android programming and I've got this project I need to finish and I'm currently stuck.
I've got a standard listview in a Menu class with an array containing around 20 different elements. So what I want to do is load images in an imageview depending on which item in the listview I click, and since I'm a beginner the only idea I had was to make a new activity for each imageview which seems like a pretty bad way to do it since I'd need about 20-30 new activities..
To sum things up what I want is:
Code for making ONE activity that will display a different image depending on which item in the listview I click, probably pretty basic coding I want as simple solution as possible.
If possible I'm also looking for a solution that includes an SQLite database that stores the URL of an image and then display it in a single activity, also depending on which item I press in my current listview.
(I hope you understand my needs, and if you need I can also post my current code for the Menu class if it helps you help me) Or you can just show me a different way to make this work, I appreciate every answer! Thanks in advance!
NOTE
And please keep in mind, I'm a noob at Java and Android so keep it rather simple or at least explain what you do.

When you click on a list item, display the image in another view in the same layout, unless you want the image to take up the entire screen real estate. If you want it in the entire screen, go to a new Activity by sending the activity an Intent.
Activities are the "controller" of your application. They interact with the visible UI and the input from the user. You don't need a separate activity for each image, just an activity that's associated with a "place" in the UI (an ImageView) where you'll display the image.
I'd start by adding the images as resources under res/drawable before going on to databases.
You are going to have to do most of this yourself. There really isn't any substitute for taking the time to learn Java and Android. There are several tutorials and Android University classes under the Resources tab in the Developers Guide; I suggest you do all of them.