android view from layout code example
Example: what is inflater in android
LINK: https://stackoverflow.com/questions/3477422/what-does-layoutinflater-in-android-do
## there are images on the website to see better what's going on.
What does LayoutInflator do?
When I first started Android programming, I was really confused by LayoutInflater and findViewById. Sometimes we used one and sometimes the other.
LayoutInflater is used to create a new View (or Layout) object from one of your xml layouts.
findViewById just gives you a reference to a view than has already been created. You might think that you haven't created any views yet, but whenever you call setContentView in onCreate, the activity's layout along with its subviews gets inflated (created) behind the scenes.
So if the view already exists, then use findViewById. If not, then create it with a LayoutInflater.
Example
Here is a mini project I made that shows both LayoutInflater and findViewById in action. With no special code, the layout looks like this.
enter image description here
The blue square is a custom layout inserted into the main layout with include (see here for more). It was inflated automatically because it is part of the content view. As you can see, there is nothing special about the code.
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
}
Now let's inflate (create) another copy of our custom layout and add it in.
enter image description here
LayoutInflater inflater = getLayoutInflater();
View myLayout = inflater.inflate(R.layout.my_layout, mainLayout, false);
To inflate the new view layout, all I did was tell the inflater the name of my xml file (my_layout), the parent layout that I want to add it to (mainLayout), and that I don't actually want to add it yet (false). (I could also set the parent to null, but then the layout parameters of my custom layout's root view would be ignored.)
Here it is again in context.
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
LinearLayout mainLayout = (LinearLayout) findViewById(R.id.activity_main_layout);
LayoutInflater inflater = getLayoutInflater();
View myLayout = inflater.inflate(R.layout.my_layout, mainLayout, false);
myLayout.setBackgroundColor(ContextCompat.getColor(this, R.color.colorAccent));
TextView textView = (TextView) myLayout.findViewById(R.id.textView);
textView.setText("New Layout");
mainLayout.addView(myLayout);
}
}
Notice how findViewById is used only after a layout has already been inflated.
Supplemental Code
Here is the xml for the example above.
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/activity_main_layout"
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:padding="16dp">
<!-- Here is the inserted layout -->
<include layout="@layout/my_layout"/>
</LinearLayout>
my_layout.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="100dp"
android:layout_height="100dp"
android:background="@color/colorPrimary">
<TextView
android:id="@+id/textView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:padding="5dp"
android:textColor="@android:color/white"
android:text="My Layout"/>
</RelativeLayout>
When do you need LayoutInflater
The most common time most people use it is in a RecyclerView. (See these RecyclerView examples for a list or a grid.) You have to inflate a new layout for every single visible item in the list or grid.
You also can use a layout inflater if you have a complex layout that you want to add programmatically (like we did in our example). You could do it all in code, but it is much easier to define it in xml first and then just inflate it.