Including layouts: a working example

Here's a working example of including one layout inside another.

Let me know if you have any issues or questions.
This works with, and probably requires, a AVD version of 2.1 or thereabouts.



contents of droidTest1.java:

package androidforbeginners.droidTest1;

import android.app.Activity;
import android.os.Bundle;

public class droidTest1 extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
}


contents of main.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="combining layouts"
/>

<include android:id="@+id/cell1" layout="@layout/layout2" />
<include android:id="@+id/cell2" layout="@layout/layout3" />


</LinearLayout>



Contents of layout2.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="100px"
android:background="#0033cc"
>
<TextView
android:layout_width="fill_parent"
android:layout_height="40px"
android:text="layout2"
/>
<CheckBox
android:layout_width="fill_parent"
android:layout_height="40px"
/>
</LinearLayout>


Contents of layout3.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="100px"
android:background="#0066cc"
>
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="layout3"
/>
<CheckBox
android:layout_width="fill_parent"
android:layout_height="wrap_content"
/>
</LinearLayout>


Output:



You could also include multiple occurrences of the one layout in your main.xml like this if you wanted:

contents of main.xml (revised):

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="combining layouts"
/>

<include android:id="@+id/cell1" layout="@layout/layout2" />
<include android:id="@+id/cell2" layout="@layout/layout2" />
<include android:id="@+id/cell3" layout="@layout/layout2" />
<include android:id="@+id/cell4" layout="@layout/layout2" />


</LinearLayout>


Although if you do this, I can't see a way to reference individual repeating items.

I think include is more including a single layout across multiple Activities.

Let me know in the comments if you know a way.

Till next time: Enjoy!

Layout Tricks: Creating Reusable UI Components

The Android platform offers a wide variety of UI widgets, small visual construction blocks that you can glue together to present users with complex and useful interfaces. However applications often need higher-level visual components. To meet that need, and to do so efficiently, you can combine multiple standard widgets into a single, reusable component.

For example, you could create a reusable component that contains a progress bar and a cancel button, a panel containing two buttons (positive and negative actions), a panel with an icon, a title and a description, and so on. You can create UI components easily by writing a custom View, but you can do it even more easily using only XML.

In Android XML layout files, each tag is mapped to an actual class instance (the class is always a subclass of View, The UI toolkit lets you also use three special tags that are not mapped to a View instance: <requestFocus />, <merge /> and <include />. This article shows how to use <include /> to create pure XML visual components.

The <include /> element does exactly what its name suggests; it includes another XML layout. Using this tag is straightforward as shown in the following example:


<com.android.launcher.Workspace
android:id="@+id/workspace"
android:layout_width="fill_parent"
android:layout_height="fill_parent"

launcher:defaultScreen="1">

<include android:id="@+id/cell1" layout="@layout/workspace_screen" />
<include android:id="@+id/cell2" layout="@layout/workspace_screen" />
<include android:id="@+id/cell3" layout="@layout/workspace_screen" />

</com.android.launcher.Workspace>


In the <include /> only the layout attribute is required. This attribute, without the android namespace prefix, is a reference to the layout file you wish to include. In this example, the same layout is included three times in a row. This tag also lets you override a few attributes of the included layout. The above example shows that you can use android:id to specify the id of the root view of the included layout; it will also override the id of the included layout if one is defined. Similarly, you can override all the layout parameters. This means that any android:layout_* attribute can be used with the <include /> tag. Here is an example:



<include android:layout_width="fill_parent" layout="@layout/image_holder" />
<include android:layout_width="256dip" layout="@layout/image_holder" />



Getting started with Android Development using Eclipse

The Google Android platform offers a easy and quick way to develop applications for the mobile device. First of all, lets start with the tools we will need to start developing our own Android applications.

The best IDE (Integrated development environment) t to develop Android is Eclipse.



The Android SDK

We will need another tool to work with Android. This tool is called the SDK (Software Development Kit), we have download it from here and place in somewhere handy on your computer (C:/Android/SDK if we are on Windows, for example, or ./home/YOURUSERNAME/Android/SDK if we use a *nix system).

It doesn't really matter where you put it, just don't forget where, because in next steps we will have to enter the path to the SDK into the Eclipse environment.


Eclipse

Once we have downloaded the SDK we will need the Android plugin for Eclipse. There are a couple of different ways of doing this, depending of the version of Eclipse you are using:

For Eclipse Ganymede :

* Start Eclipse.
* In the Menu, select "Help" and then "Software Updates".
* In the new pop-up window, push the button "Add site ... " and enter the following address and click Ok:

https://dl-ssl.google.com/android/eclipse/

*
* Once this is done, you have to go back to the Updates and Add ons menu. The location we have entered before should appear, click on it, check the "Developer Tools" and click Install.
* Follow the steps to install the plugin.

For Eclipse Europa version

* Start Eclipse
* In the Menu, select "Help" , "Software Updates" and then "Find and Install".
* Click on New Remote Site
* In the new pop-up window, paste 'https://dl-ssl.google.com/android/eclipse/', and click Ok:

* One this is done, the new site should appear in the Add ons list. Click on it and check both “Android Developer Tools” and “Android Editor”.
* Follow the steps to install the plugin.

Hint: If the https://dl-ssl.google.com/android/eclipse/ doest work try "http" instead of "https".

Once we have installed the Eclipse plugin we have to restart the IDE. Now, its time to point to the plugin where the SDK is in our system.

In the Menu, “Window”, select “Preferences”. Select Android from the left panel, click the “Browse” button and locate the SDK directory in your computer, then click OK.

Now we are able to create Android applications on our Eclipse IDE.

How to Install .Apk Apps on you Google Android Phones

1. Install and open the Apps Installer application from the "Android Market".

2. This opens a view showing *.apk application names in the sdcard root directory.(note, if no AppNames are listed you have no .apk files in the root directory of the SDCard)

3. Touch the app name to initiate installation of the app.

4. The app is now installed

How to Non-Market .Apk Application on your Google Android Phones

1. Download and install Google Android SDK. The tool you need is adb.exe.

2. Now type adb in a command shell will display all the options, adb.exe is SDK tool used to install applications and interface with the device.

3. Now Connect Your Android Phone to your computer using USB cable. You need to install Drivers for this. Download Android USB drivers from here. This driver is required for adb to interface with an android phone using USB cable.

4. Go to Android Settings/SD card & phone storage and disable Use for USB storage. You can enable it again later after you installed your third-party application.

5. Go to Settings/Application settings and enable Unknown sources.

6. Connect the G1 to your computer using the USB cable and install the driver you downloaded in step 3. After installing the driver you should see ADB Inteface in Windows Device Manager.

7. If you made it this far, download the APK file to a local folder on your computer, something like C:\MyAPKs will work fine and install it using ADB. The command would be adb install c:\myapks\ and that’s about it.

Anyway, the apk files refers to the Android Package files; and there are numbers of freeware you can try.

The difference between @+id and @android:id

Sometimes you see references in your layout files like:

<listview id="@+id/android:list">

and

<listview id="@android:id/list">

What's the difference?
.. I'm glad you asked ☺

@+id/foo means you are creating an id named foo in the namespace of your application.
You can refer to it using @id/foo.
@android:id/foo means you are referring to an id defined in the android namespace.

The '+' means to create the symbol if it doesn't already exist. You don't need it (and shouldn't use it) when referencing android: symbols, because those are already defined for you by the platform and you can't make your own in that namespace anyway.

This namespace is the namespace of the framework.
for example, you need to use @android:id/list because this the id the framework expects to find.. (the framework knows only about the ids in the android namespace.)

Android Activities

An activity presents a visual user interface for one focused endeavor the user can undertake.

For example, an activity might present a list of menu items users can choose from or it might display photographs along with their captions. A text messaging application might have one activity that shows a list of contacts to send messages to, a second activity to write the message to the chosen contact, and other activities to review old messages or change settings.

Though they work together to form a cohesive user interface, each activity is independent of the others. Each one is implemented as a subclass of the Activity base class.

An application might consist of just one activity or, like the text messaging application just mentioned, it may contain several. What the activities are, and how many there are depends, of course, on the application and its design.

Typically, one of the activities is marked as the first one that should be presented to the user when the application is launched. Moving from one activity to another is accomplished by having the current activity start the next one.

Each activity is given a default window to draw in. Typically, the window fills the screen, but it might be smaller than the screen and float on top of other windows.

An activity can also make use of additional windows — for example, a pop-up dialog that calls for a user response in the midst of the activity, or a window that presents users with vital information when they select a particular item on-screen.

The visual content of the window is provided by a hierarchy of views — objects derived from the base View class. Each view controls a particular rectangular space within the window. Parent views contain and organize the layout of their children. Leaf views (those at the bottom of the hierarchy) draw in the rectangles they control and respond to user actions directed at that space. Views are, therefore, where the activity's interaction with the user takes place.

For example, a view might display a small image and initiate an action when the user taps that image. Android has a number of ready-made views that you can use — including buttons, text fields, scroll bars, menu items, check boxes, and more.

A view hierarchy is placed within an activity's window by the Activity.setContentView() method. The content view is the View object at the root of the hierarchy.

Activity Lifecycle

Activities in the system are managed as an activity stack.
When a new activity is started, it is placed on the top of the stack and becomes the running activity -- the previous activity always remains below it in the stack, and will not come to the foreground again until the new activity exits.

An activity has essentially four states:

If an activity in the foreground of the screen (at the top of the stack), it is active or running.

If an activity has lost focus but is still visible (that is, a new non-full-sized or transparent activity has focus on top of your activity), it is paused.

A paused activity is completely alive (it maintains all state and member information and remains attached to the window manager), but can be killed by the system in extreme low memory situations.

If an activity is completely obscured by another activity, it is stopped.

It still retains all state and member information, however, it is no longer visible to the user so its window is hidden and it will often be killed by the system when memory is needed elsewhere.

If an activity is paused or stopped, the system can drop the activity from memory by either asking it to finish, or simply killing its process. When it is displayed again to the user, it must be completely restarted and restored to its previous state.

There are three key loops you may be interested in monitoring within your activity:

The entire lifetime of an activity happens between the first call to onCreate(Bundle) through to a single final call to onDestroy().

An activity will do all setup of "global" state in onCreate(), and release all remaining resources in onDestroy(). For example, if it has a thread running in the background to download data from the network, it may create that thread in onCreate() and then stop the thread in onDestroy().

The visible lifetime of an activity happens between a call to onStart() until a corresponding call to onStop(). During this time the user can see the activity on-screen, though it may not be in the foreground and interacting with the user. Between these two methods you can maintain resources that are needed to show the activity to the user.

For example, you can register an IntentReceiver in onStart() to monitor for changes that impact your UI, and unregister it in onStop() when the user an no longer see what you are displaying. The onStart() and onStop() methods can be called multiple times, as the activity becomes visible and hidden to the user.

The foreground lifetime of an activity happens between a call to onResume() until a corresponding call to onPause(). During this time the activity is in front of all other activities and interacting with the user.

An activity can frequently go between the resumed and paused states -- for example when the device goes to sleep, when an activity result is delivered, when a new intent is delivered -- so the code in these methods should be fairly lightweight.

The entire lifecycle of an activity is defined by the following Activity methods. All of these are hooks that you can override to do appropriate work when the activity changes state. All activities will implement onCreate(Bundle) to do their initial setup; many will also implement onPause() to commit changes to data and otherwise prepare to stop interacting with the user.

You should always call up to your superclass when implementing these methods.

protected void onCreate(Bundle icicle);

Called when the activity is first created. This is where you should do all of your normal static set up: create views, bind data to lists, etc. This method also provides you with a Bundle containing the activity's previously frozen state, if there was one.

Always followed by ..




protected void onStart();

Called when the activity is becoming visible to the user.

Followed by onResume() if the activity comes to the foreground, or onStop() if it becomes hidden.

protected void onRestart();

Called after your activity has been stopped, prior to it being started again. Always followed by onStart()

protected void onResume();
Called when the activity will start interacting with the user. At this point your activity is at the top of the activity stack, with user input going to it.

Always followed by onPause().

protected void onPause();
Called when the system is about to start resuming a previous activity. This is typically used to commit unsaved changes to persistent data, stop animations and other things that may be consuming CPU, etc. Implementations of this method must be very quick because the next activity will not be resumed until this method returns.

Followed by either onResume() if the activity returns back to the front, or onStop() if it becomes invisible to the user.

protected void onStop();
Called when the activity is no longer visible to the user, because another activity has been resumed and is covering this one. This may happen either because a new activity is being started, an existing one is being brought in front of this one, or this one is being destroyed.

Followed by either onRestart() if this activity is coming back to interact with the user, or onDestroy() if this activity is going away.

protected void onDestroy();
The final call you receive before your activity is destroyed. This can happen either because the activity is finishing (someone called finish() on it, or because the system is temporarily destroying this instance of the activity to save space. You can distinguish between these two scenarios with the isFinishing() method.

A first hand look at building an Android application