Now I explain one by one first of all we see the architecture of file formed
There many important file and directories are created.
AndroidManifest.xml : It is configuration file which is formed for Helloandroid application
Default.properties or project.properties: It is used by Eclipse and android. Hence please do not edit this file.
/gen/hell.abh.com/HelloandroidActivity.java: The name of Application which is created i.e. named as "HelloandroidActivity"
/gen/hell.abh.com/R.java: It is generated Resource file do not edit this file.
/assets folder:Here uncomplied file resource stored.
/res folder: it is place where application resource include such as graphic,animation ,layout file and row file.
/res/drawable:Application icon graphic resource which is default stored.
/res/layout/main.xml: It is layout file used for Helloandroid project.It is very important file.
/res/values/string.xml: It is path where string resources are defined. Here string is resources for android. actually it is value folder it is very important folder it define resouces such as
arrays.xml-Xml file define the array
colors.xml-Xml file define color.It define background color for UI
dimens.xml-Xml file which define value of UI eg 40px,40px by R.dimens class,
string.xml-Xml file used to define text String to be used in your application
styles.xml-Xml file which is define the style of application
I am going to explain the main.xml which lie under /res/layout/main.xml
The layout of the application can be determine by the xml.file or source code . main.xml is a file which determine the layout your application i.e. user interface before explaining each line of main.xml I want to tell what is view ?
View: Views are user interface as object such as button or TextField, Radiobutton etc. and ViewGroup is container which determine how the views are laid out such as Grid or vertical. you would notice one important thing by seeing the above chart it is clear that ViewGroup may consist of ViewGruop and View also but View can never consist ViewGroup.
When you make any new android application. Two view is always formed LinearLayout and TextView .
Line 1:<?xml version="1.0" encoding="utf-8"?>
xml version="1.0" is simple version which is used currently specify in form of "1.x"
encoding ="utf-8" It may be possible that Xml file may contain the non ASCII characters, so we have to use unicode
Line 2:<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
<LinearLayout is Tag of LinearLayout which is default defined in the android application LinearLayout Tag.The namespace is defined by the xmlns attribute in the start tag(LinearLayout) of an element.The namespace declaration has the following syntax. xmlns:prefix="URI". namespace(prefix android) is used in each line main.xml file.
Line 3: android:layout_width="fill_parent"
android is namespace and layout_width is the attribute of LinearLayout tag. fill_parent is value of attribute .fill_parents stretches the contents to fill container.you can choose the number of value by pressing CTRL+SPACEBAR
Line 4: android:layout_height="fill_parent"
layout_height is attribute of LinearLayout tag. The value of layout_height is fill_parent and wrap_content.The wrap_content means Views occupies the place in container as it should be.
Line 5:android:orientation="vertical"
android:orientation define the layout orientation it may be specify the vertical or Horizontal
Line 6:<TextView
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/hello" />
android:text="@string/hello" />
There is two method for set the android:text
(1) The first Method is the set the android:text attribute to raw string
<TextView
-----------
-----------
android:text="It is my first porgram" />
(2)The second method is the use the string resources called "my_program" which should be define in string.xml file
<TextView
-----------
-----------
android:text="@string/my_program" />
When you use first method android SDK give warning "Hardcoded string "hello", should use @string resource" you may ignore. when you use second method you must edit explcity in string.xml file in resource file
<?xml version="1.0" encoding="utf-8"?>
<resources>
<string name="hello">It is my first android program</string>
<string name="app_name">Helloandroid</string>
</resources>
but i prefer that you must use second method.
It is Graphical representaion of string.xml. Here is two string resouce is given
hello(String)
app_name(String)
you can change the value of both attribute.Here we change the value of Hello string "It is my first android program". you must save before going forward
When you change These change reflect in the file (string.xml). resource file when you edit
String resources through the Graphical mode, automatically string.xml resource file updated
Now execute the program once again.your change will reflect in program.
package hello.abh.com;
import android.app.Activity;
import android.os.Bundle;
public class HelloandroidActivity extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
}
Line 1: package hell.abh.com this is namespace conversion in every android application
Line 2: import android.app.Activity Since each application is start with a activity Activity is necessary to imported
Line 3: import android.os.Bundle is another package which is needed.
Line 4: HelloandroidActivity is our class which extends Activity class.
Line 5:public void onCreate(Bundle savedInstanceState) it is method of Activity class which is overridden it has parameter savedInstanceState.It is current state information is bundled as savedInstanceState in other word we can say that All current state information is bundled as in savedInstanceState that is object which held in memory.Here we will not directly handle but we must be aware of the presence
Line 6:super.onCreate(savedInstanceState) This line is very important because it call to base Activity class to perform setup work for Helloandroid. If you do not write this line , you will receive run-time exception error. Remember it always call under onCreate(BudlesavedInstanceState)
Before explaining the line setContentView(R.layout.main) we want to tell what is R in this code
R is stand for Resources. we have been talking about only two file main.xml and Helloandroid.java.source file.main.xml is a xml file which determine the layout of the application and Helloandroid is source code which used main.xml file with the help or R.class file.R.class file act as communication link between your source code and main.xml file.
It has all reference ID of all the resources in your
There are two ways you can access a resource:
Android is based upon the MVC pattern but There is no programming which is universally perfectly framed in MVC pattern. MVC is a concept rather than a programming framework . You can implement your own MVC in any platforms. As long as you stick to the following basic idea
/assets folder:Here uncomplied file resource stored.
/res folder: it is place where application resource include such as graphic,animation ,layout file and row file.
/res/drawable:Application icon graphic resource which is default stored.
/res/layout/main.xml: It is layout file used for Helloandroid project.It is very important file.
/res/values/string.xml: It is path where string resources are defined. Here string is resources for android. actually it is value folder it is very important folder it define resouces such as
arrays.xml-Xml file define the array
colors.xml-Xml file define color.It define background color for UI
dimens.xml-Xml file which define value of UI eg 40px,40px by R.dimens class,
string.xml-Xml file used to define text String to be used in your application
styles.xml-Xml file which is define the style of application
I am going to explain the main.xml which lie under /res/layout/main.xml
The layout of the application can be determine by the xml.file or source code . main.xml is a file which determine the layout your application i.e. user interface before explaining each line of main.xml I want to tell what is view ?
View: Views are user interface as object such as button or TextField, Radiobutton etc. and ViewGroup is container which determine how the views are laid out such as Grid or vertical. you would notice one important thing by seeing the above chart it is clear that ViewGroup may consist of ViewGruop and View also but View can never consist ViewGroup.
When you make any new android application. Two view is always formed LinearLayout and TextView .
Line 1:<?xml version="1.0" encoding="utf-8"?>
xml version="1.0" is simple version which is used currently specify in form of "1.x"
encoding ="utf-8" It may be possible that Xml file may contain the non ASCII characters, so we have to use unicode
Line 2:<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
<LinearLayout is Tag of LinearLayout which is default defined in the android application LinearLayout Tag.The namespace is defined by the xmlns attribute in the start tag(LinearLayout) of an element.The namespace declaration has the following syntax. xmlns:prefix="URI". namespace(prefix android) is used in each line main.xml file.
Line 3: android:layout_width="fill_parent"
android is namespace and layout_width is the attribute of LinearLayout tag. fill_parent is value of attribute .fill_parents stretches the contents to fill container.you can choose the number of value by pressing CTRL+SPACEBAR
Line 4: android:layout_height="fill_parent"
layout_height is attribute of LinearLayout tag. The value of layout_height is fill_parent and wrap_content.The wrap_content means Views occupies the place in container as it should be.
Line 5:android:orientation="vertical"
android:orientation define the layout orientation it may be specify the vertical or Horizontal
Line 6:<TextView
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/hello" />
TextView
is simple a Text.android:layout_width="fill_parent" and
android:layout_height="wrap_content" has a same explanation as i above
is given
android:text="@string/hello" />
There is two method for set the android:text
(1) The first Method is the set the android:text attribute to raw string
<TextView
-----------
-----------
android:text="It is my first porgram" />
(2)The second method is the use the string resources called "my_program" which should be define in string.xml file
<TextView
-----------
-----------
android:text="@string/my_program" />
When you use first method android SDK give warning "Hardcoded string "hello", should use @string resource" you may ignore. when you use second method you must edit explcity in string.xml file in resource file
<?xml version="1.0" encoding="utf-8"?>
<resources>
<string name="hello">It is my first android program</string>
<string name="app_name">Helloandroid</string>
</resources>
but i prefer that you must use second method.
hello(String)
app_name(String)
you can change the value of both attribute.Here we change the value of Hello string "It is my first android program". you must save before going forward
When you change These change reflect in the file (string.xml). resource file when you edit
String resources through the Graphical mode, automatically string.xml resource file updated
Now execute the program once again.your change will reflect in program.
import android.app.Activity;
import android.os.Bundle;
public class HelloandroidActivity extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
}
Line 1: package hell.abh.com this is namespace conversion in every android application
Line 2: import android.app.Activity Since each application is start with a activity Activity is necessary to imported
Line 3: import android.os.Bundle is another package which is needed.
Line 4: HelloandroidActivity is our class which extends Activity class.
Line 5:public void onCreate(Bundle savedInstanceState) it is method of Activity class which is overridden it has parameter savedInstanceState.It is current state information is bundled as savedInstanceState in other word we can say that All current state information is bundled as in savedInstanceState that is object which held in memory.Here we will not directly handle but we must be aware of the presence
Line 6:super.onCreate(savedInstanceState) This line is very important because it call to base Activity class to perform setup work for Helloandroid. If you do not write this line , you will receive run-time exception error. Remember it always call under onCreate(BudlesavedInstanceState)
R is stand for Resources. we have been talking about only two file main.xml and Helloandroid.java.source file.main.xml is a xml file which determine the layout of the application and Helloandroid is source code which used main.xml file with the help or R.class file.R.class file act as communication link between your source code and main.xml file.
It has all reference ID of all the resources in your
res/ directory .source code link the main.xml file through the reference IDs which is generated in R.Java file.
if you see carefully R.java file four reference id ic_launcher,main,app_name,hell. When you complied your application There is
aapt tool that generate R. class.
I
told you that R.java file create all Reference id for /res folder if
you see carefully in the Right hand of panel you will see
ic_launcher.png under /res/drawable-hdpi file that is default image which shown when you execute the program.There is main.xml under /res/layout/main.xml and /res/values/string.xml first one is main.xml resource and latter strings.xml resource
- In source code: By using syntex:eg Syntex- R. resource type.resource name
R.string.hello.actually since it is static class
stringis the resource type andhellois the resource name. - In XML file: By using a special XML syntax that also use resource ID defined in your
Rclass, such as:@string/hello
stringis the resource type andhellois the resource name. You can use this syntax in an XML resource any place.
Android is based upon the MVC pattern but There is no programming which is universally perfectly framed in MVC pattern. MVC is a concept rather than a programming framework . You can implement your own MVC in any platforms. As long as you stick to the following basic idea
- Model: What to render
- View: How to render
- Controller: Events, user interface input
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