FragmentPagerAdapter VS FragmentStatePagerAdapter

FragmentPagerAdapter

This version of the pager is best for use when there are a handful of typically more static fragments to be paged through, such as a set of tabs. The fragment of each page the user visits will be kept in memory, though its view hierarchy may be destroyed when not visible. This can result in using a significant amount of memory since fragment instances can hold on to an arbitrary amount of state. For larger sets of pages, consider FragmentStatePagerAdapter.


FragmentStatePagerAdapter

This version of the pager is more useful when there are a large number of pages, working more like a list view. When pages are not visible to the user, their entire fragment may be destroyed, only keeping the saved state of that fragment. This allows the pager to hold on to much less memory associated with each visited page as compared to FragmentPagerAdapter at the cost of potentially more overhead when switching between pages.

• FragmentPagerAdapter stores the whole fragment in memory, and could increase a memory overhead if a large amount of fragments are used in ViewPager.
• In contrary its sibling, FragmentStatePagerAdapter only stores the savedInstanceState of fragments, and destroys all the fragments when they lose focus.
• Therefore FragmentStatePagerAdapter should be used when we have to use dynamic fragments, like fragments with widgets, as their data could be stored in the savedInstanceState.Also it wont affect the performance even if there are large number of fragments.
• In contrary its sibling FragmentPagerAdapter should be used when we need to store the whole fragment in memory.
• When I say the whole fragment is kept in memory it means, its instances wont be destroyed and would create a memory overhead. Therefore it is advised to use FragmentPagerAdapter only when there are low number of fragments for ViewPager.
• It would be even better if the fragments are static, since they would not be having large amount of objects whose instances would be stored.

To be more detail,

FragmentStatePagerAdapter:

• with FragmentStatePagerAdapter,your unneeded fragment is destroyed.A transaction is committed to completely remove the fragment from your activity's FragmentManager.
• The state in FragmentStatePagerAdapter comes from the fact that it will save out your fragment's Bundle from savedInstanceState when it is destroyed.When the user navigates back,the new fragment will be restored using the fragment's state.

FragmentPagerAdapter:

• By comparision FragmentPagerAdapter does nothing of the kind.When the fragment is no longer needed.FragmentPagerAdapter calls detach(Fragment) on the transaction instead of remove(Fragment).
• This destroy's the fragment's view but leaves the fragment's instance alive in the FragmentManager.so the fragments created in the FragmentPagerAdapter are never destroyed.

OOPS Concept

Abstraction

abstraction is a process of hiding the implementation details from the user, only the functionality will be provided to the user. In other words, the user will have the information on what the object does instead of how it does it.

Abstract Class

A class which contains the abstract keyword in its declaration is known as abstract class.

• Abstract classes may or may not contain abstract methods, i.e., methods without body ( public void get(); )
• But, if a class has at least one abstract method, then the class must be declared abstract.
• If a class is declared abstract, it cannot be instantiated.
• To use an abstract class, you have to inherit it from another class, provide implementations to the abstract methods in it.
• If you inherit an abstract class, you have to provide implementations to all the abstract methods in it.

Abstract Methods

If you want a class to contain a particular method but you want the actual implementation of that method to be determined by child classes, you can declare the method in the parent class as an abstract.

• abstract keyword is used to declare the method as abstract.
• You have to place the abstract keyword before the method name in the method declaration.
• An abstract method contains a method signature, but no method body.
• Instead of curly braces, an abstract method will have a semoi colon (;) at the end.

                                           

                                                inheritance

Inheritance allows a Child class to inherit properties from its parent class. In Java this is achieved by using extends keyword. Only properties with access modifier public and protected can be accessed in child class.

What is multiple inheritance and does java support?

Ans) If a child class inherits the property from multiple classes is known as multiple inheritance. Java does not allow to extend multiple classes. The problem with with multiple inheritance is that if multiple parent classes have a same method name, then at runtime it becomes diffcult for the compiler to decide which method to execute from the child class. To overcome this problem it allows to implement multiple Interfaces. The problem is commonly referred as What is Diamond Problem.

                                              Encapsulation

Binding (or wrapping) code and data together into a single unit is known as encapsulation. For example: capsule, it is wrapped with different medicines.

In encapsulation, the variables of a class will be hidden from other classes, and can be accessed only through the methods of their current class.

The encapsulation is achieved by combining the methods and attribute into a class. The class acts like a container encapsulating the properties. The users are exposed mainly public methods.The idea behind is to hide how thinigs work and just exposing the requests a user can do.Encapsulation is used for access restriction to a class members and methods.

Access modifier keywords are used for encapsulation in object oriented programming. For example, encapsulation in java is achieved using private, protected and public keywords.

                                        

                           Polymorphism

When one task is performed by different ways i.e. known as polymorphism. For example: to convince the customer differently, to draw something e.g. shape or rectangle etc.

In java, we use method overloading and method overriding to achieve polymorphism.

Another example can be to speak something e.g. cat speaks meaw, dog barks woof etc.

Mehtod overriding: Overriding occurs when a class method has the same name and signature as a method in parent class. When you override methods, JVM determines the proper method to call at the program’s run time, not at the compile time.

Overloading: Overloading is determined at the compile time. It occurs when several methods have same names with:

• Different method signature and different number or type of parameters.
• Same method signature but different number of parameters.
• Same method signature and same number of parameters but of different type

Example of Overloading

int add(int a,int b)
 float add(float a,int b)
 float add(int a ,float b)
 void add(float a)
 int add(int a)
 void add(int a) //error conflict with the  method int add(int a)

class BookDetails {
  String title;
  setBook(String title){}
}
class ScienceBook extends BookDetails {
  setBook(String title){} //overriding
  setBook(String title, String publisher,float price){} //overloading
}

Code Standand

• Bad coding
• Not following standard
• Not keeping performance in mind
• History, Indentation, Comments are not appropriate.
• Readability is poor
• Open files are not closed
• Allocated memory has not been released
• Too many global variables.
• Too much hard coding.
• Poor error handling.
• No modularity.
• Repeated code.

Secure An adroid app

https://code.tutsplus.com/articles/how-to-secure-an-android-app--cms-26385

Activity And FragmentActivity

A FragmentActivity is a subclass of Activity that was built for the Android Support Package.

The FragmentActivity class adds a couple new methods to ensure compatibility with older versions of Android, but other than that, there really isn't much of a difference between the two. Just make sure you change all calls to getLoaderManager() and getFragmentManager() to getSupportLoaderManager() and getSupportFragmentManager() respectively.

1. Fragment is a part of an activity, which contributes its own UI to that activity. Fragment can be thought like a sub activity. Where as the complete screen with which user interacts is called as activity. An activity can contain multiple fragments.Fragments are mostly a sub part of an activity.
2. An activity may contain 0 or multiple number of fragments based on the screen size. A fragment can be reused in multiple activities, so it acts like a reusable component in activities.
3. A fragment can't exist independently. It should be always part of an activity. Where as activity can exist with out any fragment in it.
4. 
   

Run other Thread in Main Thread

Make sure that your background worker threads have access to a Context object (can be the Application context or the Service context). Then just do this in the background worker thread:

// Get a handler that can be used to post to the main thread
Handler mainHandler = new Handler(context.getMainLooper());

Runnable myRunnable = new Runnable() {
    @Override 
    public void run() {....} // This is your code
};
mainHandler.post(myRunnable);

Gladle

Gradle is an automated build toolkit that allows the way in which projects are built to be configured and managed through a set of build configuration files. This includes defining how a project is to be built, what dependencies need to be fulfilled for the project to build successfully and what the end result (or results) of the build process should be. The strength of Gradle lies in the flexibility that it provides to the developer. The Gradle system is a self-contained, command-line based environment that can be integrated into other environments through the use of plug-ins. In the case of Android Studio, Gradle integration is provided through the appropriately named Android Studio Plug-in.

Although the Android Studio Plug-in allows Gradle tasks to be initiated and managed from within Android Studio, the Gradle command-line wrapper can still be used to build Android Studio based projects, including on systems on which Android Studio is not installed.

The configuration rules to build a project are declared in Gradle build files and scripts based on the Groovy programming language.

http://www.techotopia.com/index.php/An_Overview_of_Gradle_in_Android_Studio