Develop Reference

Is it bad proactive to create backing subclasses for your layouts if they don't need customization?

I'm new to Android and have recently started adopting the pattern to create an auto-layout-loading custom view based on a layout file. In the layout you use the 'merge' tag as the root, then in the constructor of your view, you inflate that layout into yourself so you are essentially the root of the merged-in controls. Right after you inflate, still in the constructor, you can find the child controls from the layout and assign them to private fields in the custom class so they will always be available, even when using recycler views.
Contrast that with including a layout. In that case, the layout has to define a root element (which can be your custom control, but in that case, you would not inflate the layout into yourself and would have to move the control lookup to onFinishInflate) but otherwise it ends up with the same view hierarchy.
In short, instead of this...
<include layout="#layout/layout_myCustomControl" />
You can now do this...
<com.mydomain.MyCustomControl />
However I find the auto-loading custom control version to be much more flexible and maintainable. The advantages of the second one are not only that you can use custom attributes in the referencing XML layouts (which you can't with the 'include' version) but it also gives you a central place to manage the code as well as layout management/control lookup.
So now I can do this...
<com.mydomain.MyCustomControl
app:myCustomAttribute="Foo" />
And if the control has to have code backing up its behavior, it's nicely encapsulated in the custom view.
Here's an example layout for the auto-loading version...
<?xml version="1.0" encoding="utf-8"?>
<merge xmlns:android="http://schemas.android.com/apk/res/android">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="This is static text in the header" />
<TextView android:id="#+id/dateTextView"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</merge>
And here's the class that uses it...
public class MainHeader extends LinearLayout
{
TextView dateTextView;
public MainHeader(Context context, #Nullable AttributeSet attrs)
{
super(context, attrs);
setOrientation(VERTICAL);
LayoutInflater.from(context).inflate(R.layout.header_main, this);
dateTextView = (TextView)findViewById(R.id.dateTextView);
dateTextView.setText(<<Code for setting date goes here>>);
}
}
But what I'm wondering is if the layout is purely static in nature--say holding a static image and fixed text--is it still considered good practice to use a custom view to represent it? I'd say yes for consistency, plus should I want to extend it in the future, you're already prepared for it and have to do so in just one place regardless of how many places it's used. In contrast, if you included the layout directly in say 20 places, you may have to update all 20 (depending on what's actually changed/needed.)
Pros for the Custom View approach:
Central location for managing layout loading and control lookup
Can support backing code implicitly/internally for updating the view.
Can use attributes when being referenced in other layout files
Better encapsulation (you can hide the layout itself from the outside world exposing behaviors via direct methods)
Can simply be 'new'd' up in code and the layout will automatically load. No inflating or casting needed.
Cons for Custom View approach
When used in Layout files, you now have to also specify width and height making usage a little more verbose.
May add extra classes to your project (not always, but sometimes.)
Again, it seems to me like a no-brainer, but I'm wondering if there's a preferred 'Androidy' way, or is it just a preference up to each developer?

Such approach will add additional level in your view trees. So you only made the UI tree more complex for no good reason. From other side, you can follow next steps to get rid of that side-effect:
<merge /> can only be used as the root tag of an XML layout
when inflating a layout starting with a <merge />, you must specify a parent
ViewGroup and you must set attachToRoot to true (see the
documentation of the inflate() method)
That's it.

Well apparently what I came up with wasn't that unique after all! Here's an article explaining in detail this exact scenario, along with the pros and cons of each. Looks like they too came to the same conclusion.
TrickyAndroid: Protip. Inflating layout for your custom view

Auto adapting Layout

I have a special requirement in one of my project. I have an ArrayList of items and I want to show the Views like in the image below.
All the brown boxes are View's (TextView or LinearLayout or Button). I want to add them in the order they are numbered. Their width depends on the content inside them i.e. length of text in the case of TextView.
When I add a new view, I want it to be on the right side of the previous view if their is space otherwise it should go in the next line/row.
How can I accomplish this?

I like to use FlowLayout. Super simple to use and doesn't require you re-inventing the wheel.
Just change your root view in the xml file to this:
<org.apmem.tools.layouts.FlowLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
>
And thats all it takes!

I used this third party library to solve this.

set Webview to render content with a specific amount of space at top of content

Goal:
I need some space at the top of the content as if the HTML starts off with <BR><BR><BR>
However, I don't want to inject a bunch of those manually because I need to control the amount of space in terms of DP's
How can it be done ?

Set the android:layout_marginTop="xxdp" in your webview attributes.
You can set the background of the activity to a specific color like white so it doesn't seem odd to the user, if you want to.

How I did it in my app was make a second empty LinearLayout and place it above the layout that includes the webview. For example:
<LinearLayout>
<LinearLayout>
</LinearLayout>
<LinearLayout>
//webview
</LinearLayout>
</LinearLayout>
And then I resized the first LinearLayout to a percentage in the GUI.
That's probably the absolute worst way to achieve your goal, but it worked for me.

custom view declared in xml

When declaring custom view in xml, what is the difference between declaring a View of a custom class, or declaring a completely custom view:
<LinearLayout>
<view class="packageName.MyView" android:id="#+id/myView" />
</LinearLayout>
and
<LinearLayout>
<packageName.myView android:id="#+id/myView" />
</LinearLayout>
?
I've created a subclass of EditText, and when instatiating it as View class=".." my Activity crashes with ClassCastException when trying to access MyView:
(MyView) myView = (MyView) findViewById(R.id.myView);
When declared as second option, everything works as expected.

I'm not 100% sure on this, but let me give it a go. A couple of things could be happening. The parser might not understand the class attribute correctly (e.g. it thinks it is part of a stylesheet). I am not sure how the parser handles the class attribute, since I have never seen or used it (in fact, I've never seen the <View> tag used either). A better explanation, though, might be this: the parser is trying to down-cast your View into packageName.myView class and fails (down-casting is always risky; up-casting is always safe).
Regardless of what is happening, I would always use the second option you listed, <packageName.myView android:id...>, instead of using the <View> tag. Reason being, it's redundant to use the <View> tag. Everything in this xml file must be a view (LinearLayout, Button, TextView, etc. are all descendants of the View class).
Hope that helps. If you're really, really curious, you could always download the source code for the parser...

Android: how to use XML for custom view layout

I'm coming from the world of GWT and UIBinder, where I'm used to defining custom components by extending Composite, and then putting all the UI layout code in a MyComponent.ui.xml file. This is a very nice way to build up components from smaller pieces.
I'm trying to achieve the same effect on Android with custom Views. I've been able to programmatically extend View, and then add objects by calling addView(textView). I'd like to be able to do that in XML, but I don't see how to associate an xml layout file with the view (apart the primary res/layout/main.xml file, which provides the primary layout for the app.
How can I layout my custom views in XML?
Edit: My question was unclear. What I'm looking to do is associate a my_widget.xml file with my customized view. Then in my_widget.xml I'd like to define various TextViews, etc, and plug them into my View class.

Use the fully qualified name of your custom view class in place of one of the built-in views. Here's a layout, for instance, that fills the window with your class:
<?xml version="1.0" encoding="utf-8"?>
<my.package.MyCustomView
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/my_view"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
/>

To construct Views from XML, use LayoutInflater.

You can use findViewById (int id) with an id defined in XML. See the example in the android doc here (scroll down to IDs).