SetContentView() is a part of android.app.Activity class. It helps to set our content or render our layout on the screen.
Based on the value given by the user, views will be inflated and rendered after the measurement of the screen, root view, and its child views. Well, here is everything you need to know about setContentView() method.
These all methods available from API level 1. Let’s talk more about these types.
This method uses layout constant from automatically generated R.java class. R.java class holds many static constant values in nested classes. So that you can access directly by specifying R class and nested class.
Nested Layout class contains layout resource constants to ease the availability of actual files in the resource directory.
At runtime, System will select the appropriate layout based on orientation and other factors like language and region. But default it will select the layout in res/layout directory. Eg:
Here, R.layout.activity_main is an integer value contained inside of layout class in R.java file. Using this integer value Android system will look in res/layout directory. That’s how android finds the correct layout.
If you are using XML layout do not try to initialize views before calling setContentView(R.layout.layout_name), because without inflating the layouts, there are no actual views in memory. It will lead to NullpointerException.
Set any view as your activity’s content. View’s height and width set to MATCH_PARENT as default.
//create a textview object
//set text to textview
You probably need to add an import android.widget.TextView; statement.
setContentView(View view, ViewGroup.Layoutparams)
Extension of setContentView(View view) method. Here you can specify view’s parameters.
You can add child views to Linearlayout using addView() method.
You can call many times setContentView() method, but it works only at the last call.
You can use setContentView() outside of the onCreate() method.
ListActivity does not use setContentView() Because it already contains a listview and use setListAdapter() to populate.
In fragments, LayoutInflater does layout rendering work with inflate() method. Just equivalent to setContentView().
Sometimes, you need to display a layout from many layouts based on any condition. Like showing login or signup page. So there is no need to create two activities. Just use if statement or other depends on your needs and do just like below.
That’s all for now. Is there any suggestions, please comment below.
If you are new to android development world, you may have doubts about the word “layout”.
So let’s start here,
In Android, layout describes the appearance of the app. Layouts are just resourced files. The instructions or content in layout decides to position your widget and make your user interface.
The layout contains view, viewgroup objects and <merge> tag. Just like HTML, It must have a root element. It can contain more GUI widgets like Button, TextView etc. Nested elements are also supported.
An app can have more than one screens based on developer needs. So you can have many layouts as you want.
Layout resource names must contain only lowercase a-z, 0-9, or underscore otherwise, you might end with an error.
How to create layout in android?
You can use XML straightforward vocabulary to specify your UI. For beginners, you can check it out drag and drop feature. It helps us to drag a view which you want and drop it wherever you want in layout design. The XML code will automatically complete by android studio.
For localization (translating strings into different languages), XML layout would be a better idea.
Note: You must put xmlns:android attribute with android namespace inside root element.
For an example: assume LinearLayout as your root element.
It’s not generally recommended. There may be occasions to make your layout at runtime. But it mixes up UI code and code that controlling app behavior. So it may become difficult to tweak and refine user interface.
Where is layout files located at?
Android studio automatically creates a directory to hold your layout files – layout subdirectory.
In your project structure
all resource files stored in res (resources folder).
How to create a layout file in android studio?
Right Click on your default layout subdirectory
New -> Layout resource file -> Enter layout Name and click OK.
Also give details of the root element, source set, Directory name and other available qualifiers.
How to rename layout file in android studio?
Right click on your layout file which want to rename
Refactor -> Rename -> give new file name -> Refactor. You can use shift + F6 key also.
Those messages in the listview are sent by my crush to me.
Yes, that was the best dream I ever had ;-).
I’m just kidding…
Let’s back to topic,
When beginners make an app for showing a collection of data, Most of them prefer ListView. It is easy to work with listview when comparing its successor RecyclerView. Although ListView becomes old now, uses of ListView still goes on.
Beginners use it well with adapter strategy. But Android API provides an easy way to build a listview.
In this tutorial you will learn to construct listview easily and less code.
The android:entries XML attribute helps us achieve our target.
Easy to populate ListView, Spinner, Gallery and ListPreference.
Only static, unchanging string data allowed. So you can’t use with data from internet, database, shared preferences etc.
How android:entries works ??
As shown in the picture, android:entries attribute needs an array resource name, not the file name which contains array resource. You can define array resource in strings.xml. Not only listview, Spinner, ListPreference, and gallery also use android:entries attribute. But gallery deprecated in API level 16. As a successor of ListView, RecyclerView doesn’t hold entries attribute.
When the user runs the app, Listview constructor takes the array resource referred in the entries attribute. Then the constructor makes an adapter itself with the simple_list_item_1 layout in SDK. Then assign it to the listview.
Actually, we just point our data to the listview, listview does the all other work.
This is the way how it works.
Create a new project
In Android Studio, create a new project File -> New -> Project
Application Name: Simple ListView Ex Company Domain: androidride.com
Android convention to use the reverse of the domain name. that’s never a problem for you. click Next
Choose your minimum SDK
It is necessary to choose the minimum SDK that you want. tick the phone and tablet checkbox for making the app for only phone and tablet.
Select empty activity template
For this project, we just need an empty activity. So just select the empty activity template and click next.
Create a new empty activity and layout
Next screen prompt for making an activity class file and its layout.
Activity Name : MainActivity
Tick the generate the layout checkbox if it’s not checked. Click finish. Now, you will see the MainActivity class
Change toolbar and status bar color
You can skip this step if you don’t want to alter the default style. Open res/values/colors.xml and paste the code below for to make a red colored toolbar.
If you wish to add other widgets to your layout, then you can add viewgroups like RelativeLayout, LinearLayout and other. Then just replace the XML namespace ( xmlns:android=”http://schemas.android.com/apk/res/android”) from listview to the root element.
Run the app. You will get the output like below.
How does ListView know did user click on list item ??
Based on tapping sound.
No, Here comes Listener. Listener waits for the events. Such as tapping, touching events.
Here we use OnItemClickListener nested class. Its onItemClick(…) method will trigger when an item in the listview clicked. So place the code that wants to run when click event happens.
Create and Instantiate listview variable
In onCreate() method, create listview variable and instantiate using findViewById(int id) method. In this case, id is listview, we must use the same id in XML description. Type cast the returned View object to the ListView.
In onItemClick(…) method, Implement code to reveal the content in listview row. First, Use adapterview’s getItemAtPosition(int position) method to retrieve the data from listview item row. getItemAtPosition() returns data as object in the given position.