Per the question here,
What's "tools:context" in Android layout files?
The 'tools' namespace reference (xmlns:tools="http://schemas.android.com/tools") has begun to appear in my layouts recently, and I want to know more. The original post only described the 'tools:context' attribute, but I have also noticed usage of the "tools:listitem" attribute appearing when I have designated a preview layout item for a listview, i.e.
<ListView
android:id="#+id/lvCustomer"
tools:listitem="#layout/customer_list_item" >
</ListView>
Are there more elements?
What brought me to this 'tools' namespace is that I want to be able to have 'preview-only' text (i.e. in a TextView or EditText) when using the layout designer in eclipse.
Currently, I assign the 'text' or 'hint' property for previewing text when arranging my layouts... but then I always have to remember to clear the preview value from within the code.
Ideally, instead of
<string name="preview_customer_name">Billy Bob's Roadhouse Pub</string>
...
<TextView
android:id="#+id/tvCustomerName"
android:text="#string/preview_customer_name"
</TextView>
have a something like:
<TextView
android:id="#+id/tvCustomerName"
tools:previewText="#string/preview_customer_name"
</TextView>
Thanks-
We've just added support for designtime attributes like this in Android Studio 0.2.11. See http://tools.android.com/tips/layout-designtime-attributes for more.
Think of them as design time helpers only.They do not get processed in actual view rendering at run time.
For example you want to set background of some view in your layout design when working on android studio so that you can make clear distinction where that particular view is.So you would normally do that with
android:background="#color/<some-color>"
Now risk is that sometimes we forget to remove that color and it gets shipped in apk.
instead you can do as follows:
tools:background="#color/<some-color>"
These changes will be local to android studio and will never get transferred to apk.
And also check out http://tools.android.com/tech-docs/tools-attributes for more options.
You will find tool attribute when you set object in graphical layout.
Listview (in graphical mode) -> right Click -> Preview List Content -> Choose Layout...
produces:
tools:listitem="#layout/customer_list_item"
See in layout XML below. There are 2 namespace in use "xmlns:android" and "xmlns:tools".
Tools namespace is used when the developer wants to define placeholder content that is only used in preview or in design time. Tools namespace is removed when we compiled the app.
So in the code below, I want to show the placeholder image (image_empty) that will only be visible at design time, and image1 will the actual image that will be shown when the application launch
Related
When I saw the TabBar and the Flyout menu in .NET Maui I started wondering if its possible to create your own global object for your application.
does anyone know how to do this?
(I want to add a status icon at the corner of my screen without having to manually add it to all pages.)
You can create a simple Floating Button and add it to your pages.
You can create an image with a transparent background in your favorite editor and then assign it a location on the Page.
You can refer to the following code:
<AbsoluteLayout>
<!--Other components-->
<ImageButton Source="icon.png"
BackgroundColor="Green"
CornerRadius="80"
AbsoluteLayout.LayoutFlags="PositionProportional"
AbsoluteLayout.LayoutBounds=".95,.95,80,80" />
</AbsoluteLayout>
I'm using android studio 4.1.1 and kotlin.
I'm trying to learn programming Android apps using Android Studio and Kotlin. I have a question that a couple of tutorials and searching threads have not answered for me. How does control pass from the MainActivity.kt class to another class, i.e: FirstFragment.kt?
I'm doing fine with other things I'm learning in tutorials, but I cannot figure this out.
Example:
I create a new Basic Activity app in Android Studio with Kotlin. In the java directory, I see these classes: FirstFragment.kt, MainActivity.kt and SecondFragment.kt.
In the res/layout/ directory, I see: activity_main.xml, content_main.xml, fragment_first.xml and fragment_second.xml.
Question 1) When the app loads in an emulator, I see the button and textView from the fragment_first.xml. How does this happen? I cannot see in the code where it says, "load fragment_first.xml".
MainActivity.kt has setContentView(R.layout.activity_main) which loads that layout. activity_main.xml has <include layout="#layout/content_main" />. But from there, I do not know where to find the code that loads the fragment_first.xml layout.
I believe that when fragment_first.xml loads, control passes from MainActivity.kt to FirstFragment.kt, yes? Question 2). Is this because of the onCreate function?
Thanks for helping me to understand this better.
There are multiple ways to load a fragment. Traditionally, you use the FragmentManager to create a Fragment transaction that tells the Activity to place a Fragment into the view hierarchy and start managing its lifecycle.
More recently, they have added the Navigation component, which can be used in place of directly using the FragmentManager.
In the current new project Basic Activity, the layout activity_main.xml includes the layout content_main. In content_main.xml, you'll see that it includes a fragment element that is set to the Fragment (using the name parameter) NavHostFragment, which is a special Fragment that the Navigation component uses to host children fragments that are specified in a navigation XML file. This fragment element also specifies the navigation xml file using the navGraph property. It specifies nav_graph.xml, which you'll find in the res/navigation directory.
If you open nav_graph.xml, you'll see that it has FirstFragment set as the home fragment, so that is what pulls it up as the first fragment that you see.
Basically, the control flow is:
Activity's onCreate() sets content view to activity_main, which includes content_main.
content_main includes a NavHostFragment that is automatically inserted in the view hierarchy so the Activity starts running it.
The NavHostFragment is set in the XML to use nav_graph, which tells it to load FirstFragment first.
An app uses ExpandableListActivity, and the usage of ExpandableListView is standard based on the document:
<ExpandableListView
android:id="#id/android:list"
android:layout_width="match_parent"
android:layout_height="0dip"
android:layout_weight="1"
android:divider="#android:color/transparent"
android:dividerHeight="5dip"
android:layout_marginTop="10dip">
</ExpandableListView>
Android Studio 3.2 has the following warning:
How can I get rid of the warning?
This is probably a typo. Change it to:
"#android:id/empty"
and
"#android:id/list"
See also https://developer.android.com/reference/android/app/ListActivity
ListActivity has a default layout that consists of a single,
full-screen list in the center of the screen. However, if you desire,
you can customize the screen layout by setting your own view layout
with setContentView() in onCreate(). To do this, your own view MUST
contain a ListView object with the id "#android:id/list" (or R.id.list
if it's in code)
I don't know what is ( id="#id/android:list")
give it an normal id ( #+id/androidlist )
and handle it in your code
but if you learn how to work with ExpandableListView
I prefer this link tutorial for you ExpandableListView Link
GL sir
The eClipse only creates one acitivity_main.xml file, but Android studio creates two xml layout files. The default layout for acitivity_main.xml is the CoordinatorLayout but for content_main.xml is RelativeLayout.
Why need two xmls ? The default is to refer activity_main as: setContentView(R.layout.activity_main), but I find setContentView(R.layout.content_main) also works.
What is the relationship between these two layouts ?
Is there any difference If I drop a button view to the content_main.xml or I drop a button view to activity_main.xml ?
Thanks
Why create 2 files :
These 2 files are created to make your work EASIER. As main file contain your stuff like FAB, toolbar in Coordinate layout. Now your content file is file in which you can make UI of view without interrupting the basic flow. I personally recommend this.
Why need two xmls ? The default is to refer activity_main as:
setContentView(R.layout.activity_main), but I find
setContentView(R.layout.content_main) also works.
These will work as after all these are layout files so can set as content view.
Is there any difference If I drop a button view to the content_main.xml or I drop a button view to activity_main.xml ?
No difference at all.
I have an app that has a screen like this (on a 10" tablet) :
Now I need to amend the app to also work on a phone. As the screens will be smaller, I want to take the "split view" UI and change it so that the left hand side list view is shown on its own, then on selecting a row the appropriate right hand side list view is then shown.
How do I handle this in the app, as one activity currently handles both listviews, and I guess the phone will need two one for each listview.
How do I detect which one to do?
thanks
See Supporting Different Screen Sizes.
Typically this is done using Fragments, but the basic idea is the same whether you use fragments or not. You create two different layouts for your Activity depending on the screen size.
Save the default layout single-pane for phones at res/layout/activity_main.xml
Save the dual-pane tablet layout at res/layout/activity_main_twopane.xml
Then you use layout alias files with the screen size qualifiers described in the link to determine when the tablet layout should be used. For example to show the dual-pane layout on large screens and on screens with at least 600dp in the widest direction (includes large screen phones such as the Galaxy S3), you could do this:
res/values-large/layout.xml contains:
<resources>
<item name="activity_main" type="layout">#layout/activity_main_twopane</item>
<bool name="twopane">true</bool>
</resources>
res/values-sw600dp/layout.xml contains:
<resources>
<item name="activity_main" type="layout">#layout/activity_main_twopane</item>
<bool name="twopane">true</bool>
</resources>
The Android system will take care of loading the proper layout file (either res/layout/activity_main.xml or res/layout/activity_main_twopane.xml) when your Activity loads the layout:
setContentView(R.layout.activity_main);
Just remember that the views that don't exist in the single-pane layout will be null when you try to access them (e.g., there won't be two ListViews anymore). Checking whether a certain View exists is one way to detect which layout you are using.
Also note the use of optional Boolean resources in XML files. This is a handy way to pass the "is it a large screen or small screen" variable to your Java code. You can access Boolean resources in your Activity like this:
boolean isTwoPane = getResources().getBoolean(R.bool.twopane);
You should have a look at the MasterDetailedFlow Navigation template. Eclipse:NewProject>check create Activity>select "MasterDetailedFlow" Navigatoin type. Have a look at Data Binding on Android