Develop Reference

How to make a layout of an activity visible through programming?

I have a layout as indicated below:
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:visibility="invisible">
<LinearLayout
android:layout_height="match_parent"
...
The associated activity is like this:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.act_login);// here is the layout
}
I'm trying to make it visible in the following way:
LinearLayout layoutActLogin = (LinearLayout) findViewById(R.layout.act_login);
layoutActLogin.setVisibility(View.VISIBLE);
But Android Studio told me that there is an error about R.layout.act_login

findViewById is for views, not layouts.
You should put an ID in your view like:
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/my_view"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:visibility="invisible">
<LinearLayout
android:layout_height="match_parent"
...
Then get the view reference and make it visible
View viewActLogin = findViewById(R.id.my_view);
viewActLogin.setVisibility(View.VISIBLE);

You can not change visibility of Layout. you can only change visibility of Views inside.
You can assign id to you view by using android:id tag in you layout. You can read more about this here.
In your case. Just give some Id to your View/ViewGroup, and reference that View from your Activity and using findViewById method and change its visibility.

You're misunderstanding how layouts and views work. Layouts define what is shown on-screen to a user during an activity, set by calling setContentView() within the Activity's onCreate() method. Views are individual elements within the layout, which are accessed with the R.id prefix using findViewById().
In your example you'll need to apply an ID to the root ConstraintLayout (using android:id) to be able to access it:
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/parent_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:visibility="invisible">
Then you can access it with:
ConstraintLayout layoutActLogin = (ConstraintLayout) findViewById(R.id.parent_layout);
layoutActLogin.setVisibility(View.VISIBLE);
EDIT Looking at your code I now realise you want to control the root ConstraintLayout, which makes my answer almost identical to Eduardo Herzer's. Leaving my answer up due to the added explanation at the beginning.

Set onClickListener on view from included layout not working

I have one layout which includes other layout inside. I tried to set onClikeListener on ImageView inside the included layout, but it's not working. But when I set background drawable it works. I don't know why. Here is my code:
//custom header
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/sticky_header"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="vertical">
<ImageView
android:id="#+id/iv_header_close"
android:layout_width="60dp"
android:layout_height="55dp"
android:background="#drawable/big_cross_icon" />
</LinearLayout>
//activity_detail
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#f1f2f6">
<include
android:id="#+id/header"
layout="#layout/custom_header"/>
</RelativeLayout>
//in Activity
View header = findViewById(R.id.header);
iv_header_close = (ImageView)header.findViewById(R.id.iv_header_close);
iv_header_close.setBackgroundDrawable(getResources().getDrawable(R.drawable.big_edit_icon));
iv_header_close.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
finish(); //not working
}
});
I wonder why I can access to child view inside included layout but can't set OnClickListner. Thank you so much :)

Create your iv_header_close like this:
ImageView iv_header_close = (ImageView) findViewById(R.id.iv_header_close);
Instead of calling finish() Try to call YourActivity.this.finish()
What's happening is that, inside the onClick of your imageview, you don't have access to your activity so you have to access your activity using YourActivity.this if you want to access the methods of your activity.

In case anybody is having the same issue five years later...
Using the onClick attribute on the view (ImageView, Button... mine was a button) inside the included layout file fixes the problem. However, note that the onClick attribute is now deprecated

Add background image to individual fragments

I have an app with multiple fragments and I would like to know how to add a background that is different for each fragment. The layout I am using has scrollable tabs which all use the same xml file. I also have a MainActivity that sets the view and an adapter for each fragment. I know you can add a background using the xml file with android:background or something of the sort as well as setting it to the view in the main activity but I can't figure out how to do it to each tab. Thank you for any help!

To add background to fragment, you have to wrap it in some container
<LinearLayout
android:id="#+id/linearlayout01"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="#ccc"
android:layout_weight="1"
android:orientation="vertical">
<fragment android:name="com.example.simplefragmentexample.LayOutOne"
android:id="#+id/frag_1"
android:layout_width="fill_parent"
android:layout_height="fill_parent" />
</LinearLayout>
If you wish to use same xml file, you should set images programmatically
LinearLayout l = (LinearLayout) findViewById(R.id.linearlayout01);
l.setBackground(Image);
or use several xmls with android:background.

You can get the root View of the fragment with the Fragment getView() method. Then you can set the background of the View using one of the setBackground() methods of the View. For example to set a random background color to each fragment:
for ( Fragment f : fragments ) {
f.getView().setBackgroundColor ( (new Random()).nextInt() );
}
PS: I never used fragments, therefore my answer could be wrong.

How to use a custom view in layout xml

I have made a custom view that I'm setting inside the onCreate() method in the Main Activity.
Like this:
compassView = new CompassView(this);
setContentView(compassView);
My question is. How do I reference the view in xml, so I can put it inside a linearlayout together with other controls?

Assuming your CompassView is a class which is placed in the Package called ,
com.android.sample
Create a XML like this,
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<com.android.sample.CompassView
android:id="#+id/compassview"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
/>
</LinearLayout>
And now as usual, setContentView(R.layout.xmlname); in your onCreate().
And compassView = (CompassView)findViewbyId(R.id.compassview);

setContentView("here put your xml layout")
In .xml layout just simple add ur View:
<com.example.widget.CompassView
android:id="#+id/..."
style="#style/..." >
</com.example.widget.CompassView>

First of all, you must override any constructor of your superclass. If you don't do that you will get a run time error and you activity will never be opened. Then you should use the fully qualified class name like this:
<your_package_name.your_class_name
android:id="#+id/mycompass"
your attributes here
...
/>

You will have to add your custom view In your xml file, something like this:
<yourpackagename.yourCustomViewClass
android:id="#+id/myCustomView"
android:layout_width="fill_parent"
android:layout_height="fill_parent" />
After this, you can access this view through its id, like you would have done for any other View

How to specify id when uses include in layout xml file

In my layout xml file, I have included other layout xml file (each
with a different android id).
<include layout="#layout/view_contact_name" android:id="+id/test1"/>
<include layout="#layout/view_contact_name" android:id="+id/test2"/>
But when I run it in the emulator, and start Hierarchy Viewer, each of
the layout still shows 'NO_ID', and in my code, I have
findViewById(R.id.test1) and findViewById(R.id.test2) both returns null.
Can anyone please help me with my problem ?

Specify the ID in the <include>
<include layout="#layout/test" android:id="#+id/test1" />
Then use two findViewById to access fields in the layout
View test1View = findViewById(R.id.test1);
TextView test1TextView = (TextView) test1View.findViewById(R.id.text);
Using that approach, you can access any field in any include you have.

I found out, that if you are using <merge> tag in your include layout, then the ID of include transfers to the merge tag which is not real view.
So either remove merge, or replace it with some layout.
Tor Norbye wrote:
The <include> tag is not a real view, so findByView will not find it. The #id attribute (and any other attributes you've set on the include tag) gets applied on the root tag of the included layout instead. So your activity.getView(R.id.included1) should in fact be the <TextView> itself.

Romain Guy indicates that you can override the ID of an included layout by putting an android:id attribute inside the <include> tag.
<include android:id="#+id/cell1" layout="#layout/workspace_screen" />

I think the top answer misses the most important point and might mislead people into thinking the <include/> tag creates a View that holds the include contents.
The key point is that include's id is passed to the root view of the include's layout file.
Meaning that this:
// activity_main.xml
<include layout="#layout/somelayout" android:id="#+id/someid"/>
// somelayout.xml
<?xml version="1.0" encoding="utf-8"?>
<ImageView
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
/>
Becomes this:
// activity_main.xml
<ImageView
android:id="#+id/someid"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
/>

yes is like this, but careful when the layout inserted in include field is a custom one and you want to access that root layout. That layout in this case #layout/test test, is actually returned in first line.
test test1View = (test)findViewById(R.id.test1);

you must set id each include tag
included child element set a
new id. if you look how to generate new id, look at this entry:
https://stackoverflow.com/a/15442898/1136117

Problem is we try to use id which is not declared in current layout file.
Instead of declaring again, id can be simply referred using #+id/. If you refactor original id name through Android Studio it does refactor in included layout as well.
<include layout="#layout/toolbar"/>
<TextView
android:id="#+id/txt_description"
android:layout_width="match_parent"
android:layout_height="wrap_content"
**android:layout_below="#+id/toolbar"**
android:layout_marginTop="16dp"
android:paddingLeft="8dp"
android:paddingRight="8dp"/>

In a case of using <RecyclerView> find the id of <include> by using an instance of inflated view or else it will return null.
public class ViewHolder extends RecyclerView.ViewHolder {
private mTextView;
public ViewHolder(View view) {
super(view);
View include_1 = view.findViewById(R.id.include_1);
mTextView = (TextView) include_1.findViewById(R.id.text_id);
}
}

If you have set id to either root tag of included layout then you can use that id
or you can set id to included layout.
But you can not set id to both it may throw exception.
<include layout="#layout/view_contact_name" android:id="+id/test1"/>
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content">
....
</LinearLayout>
Or
<include layout="#layout/view_contact_name"/>
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
android:id="#+id/llBottomMainView"
android:layout_width="match_parent"
android:layout_height="wrap_content">
....
</LinearLayout>

When talking about include you either have an id on the root view inside the included layout file or on the include line itself and not on both. For example:
<include layout="#layout/layout1" android:id="#+id/layout1"/>
Layout 1 file
<RelativeLayout
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="#+id/layout2">
</RelativeLayout>
The above example is wrong because technically you have two id's declared for the same layout. So what you have to do is pick which element will have the id.

To specify the id when you are including a xml file is like setting it to any xml element
Example:
*list_layout.xml*
`<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<androidx.recyclerview.widget.RecyclerView
android:id="#+id/rvNames"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
</LinearLayout>`
*activity_main.xml*
`<RelativeLayout
tools:context=".MainActivity">
<include
layout="#layout/list_layout"
android:id="#+id/myList" />
</RelativeLayout>`
Now if you want to get that to use in .kt file, just use normally findViewById
Exemplo
*MainActivity.kt*
`val myList: RecycleView = findViewById(R.id.myList)`

Wow, I can't believe this question doesn't have the right answer yet. It's simple tags suck. You can only change things that start with android:layout_ which android:id doesn't match. So the answer is you can't. Sorry. What you can do instead is create a class that will be a ViewGroup which will inflate the included views inside, then add that as a tag in your layout, but that's about it.