Using the Application Class
Depending on what you're doing in your initialization you could consider creating a new class that extends Application and moving your initialization code into an overridden onCreate method within that class.
public class MyApplicationClass extends Application {
@Override
public void onCreate() {
super.onCreate();
// TODO Put your application initialization code here.
}
}
The onCreate in the application class is only called when the entire application is created, so the Activity restarts on orientation or keyboard visibility changes won't trigger it.
It's good practice to expose the instance of this class as a singleton and exposing the application variables you're initializing using getters and setters.
NOTE: You'll need to specify the name of your new Application class in the manifest for it to be registered and used:
<application
android:name="com.you.yourapp.MyApplicationClass"
Reacting to Configuration Changes [UPDATE: this is deprecated since API 13; see the recommended alternative]
As a further alternative, you can have your application listen for events that would cause a restart – like orientation and keyboard visibility changes – and handle them within your Activity.
Start by adding the android:configChanges node to your Activity's manifest node
<activity android:name=".MyActivity"
android:configChanges="orientation|keyboardHidden"
android:label="@string/app_name">
or for Android 3.2 (API level 13) and newer:
<activity android:name=".MyActivity"
android:configChanges="keyboardHidden|orientation|screenSize"
android:label="@string/app_name">
Then within the Activity override the onConfigurationChanged method and call setContentView to force the GUI layout to be re-done in the new orientation.
@Override
public void onConfigurationChanged(Configuration newConfig) {
super.onConfigurationChanged(newConfig);
setContentView(R.layout.myLayout);
}
OK, let's separate the question of the characters that:
- aren't valid at all in any XML document.
- need to be escaped.
The answer provided by @dolmen in "What are invalid characters in XML" is still valid but needs to be updated with the XML 1.1 specification.
1. Invalid characters
The characters described here are all the characters that are allowed to be inserted in an XML document.
1.1. In XML 1.0
The global list of allowed characters is:
[2] Char ::= #x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD] | [#x10000-#x10FFFF] /* any Unicode character, excluding the surrogate blocks, FFFE, and FFFF. */
Basically, the control characters and characters out of the Unicode ranges are not allowed.
This means also that calling for example the character entity  is forbidden.
1.2. In XML 1.1
The global list of allowed characters is:
[2] Char ::= [#x1-#xD7FF] | [#xE000-#xFFFD] | [#x10000-#x10FFFF] /* any Unicode character, excluding the surrogate blocks, FFFE, and FFFF. */
[2a] RestrictedChar ::= [#x1-#x8] | [#xB-#xC] | [#xE-#x1F] | [#x7F-#x84] | [#x86-#x9F]
This revision of the XML recommendation has extended the allowed characters so control characters are allowed, and takes into account a new revision of the Unicode standard, but these ones are still not allowed : NUL (x00), xFFFE, xFFFF...
However, the use of control characters and undefined Unicode char is discouraged.
It can also be noticed that all parsers do not always take this into account and XML documents with control characters may be rejected.
2. Characters that need to be escaped (to obtain a well-formed document):
The < must be escaped with a < entity, since it is assumed to be the beginning of a tag.
The & must be escaped with a & entity, since it is assumed to be the beginning a entity reference
The > should be escaped with > entity. It is not mandatory -- it depends on the context -- but it is strongly advised to escape it.
The ' should be escaped with a ' entity -- mandatory in attributes defined within single quotes but it is strongly advised to always escape it.
The " should be escaped with a " entity -- mandatory in attributes defined within double quotes but it is strongly advised to always escape it.
Best Answer
to use white space in xml as string use
 . XML won't take white space as it is. it will trim the white space before setting it. So use instead of single white space