Do you know SMTP? is it use SOAP or REST?

Ans : 

SMTP : SMTP (Simple Mail Transfer Protocol) is a TCP/IP protocol used in sending and receiving e-mail.

SOAP and REST both allow you to create your own API. API stands for Application Programming Interface. It makes it possible to transfer data from an application to other applications. An API receives requests and sends back responses through internet protocols such as HTTP, SMTP, and others.

It use SOAP web-service. SOAP is protocol and rules are maintained by World wide web consortium(W3C).

Design such button in that text should be displayed below image

Ans : 

1) Select button and go to Attribute Inspector in your storyboard.

2) Assign Image to the button. (Don't use background Image)

3) Set Title text to that button.

4) Now you need to set edge and Inset so first select image from edge and set Inset as you need and then select title from edge and set inset as per your need.

Difference between viewdidload and viewwillappear?

Ans : 

ViewDidLoad - It is excecuted once. So writer settings like set label text in ViewDidLoad.

ViewWillAppear - It is called every time when view appear.

ViewDidLoad - It is called when view is begin constructed.

ViewWillAppear - When view is about ready to appear.

ViewDidLoad :  It is automatically called when view controller completely loaded into memory. Override this method to perform additional initialization on views that were loaded from xib.

I.e instance variable initialization, database access, network request

ViewWillAppear :  It is called when View is about to added on view hierachy. If we want to change some, then we have to override this method.Like change orientation, change screen data.

Suppose your tableview data will be changed periodically. Then you have to write [tableview reloaddata] in ViewWillApper.

Read UIViewController LifeCycle

What are join in sql? Explain Types of Join

Ans :

Join : When we need data from more than 1 table, then we can fetch data from those table using joining those table. It will return only matching data from two tables.

Select * from table1 t1 inner join table2 t2 on t1.column1 = t2.column1

Types of Join :

1. Inner Join : If we use inner join between two table, then only data exists in both table, are returned.

2. Outer Join :
    Left Outer Join : It returns all data from left table(table1) and only matching data from both table.
    Right Outer Join : It returns all data from right table(table2) and only matching data from both table.

3. Cross Join : It is like cartesian join. It returns all records from both table and it returns table1.count * table2.count records in returns. Suppose table1 has 4 records and table2 has 3 records and returns 4*3 records.

4. Self Join : If some column's reference has in same table then self join is used. It is same like inner join but here both left and right table are same. Its like if you table and Columns are such as MainID, Name, ParentID then you can make query like
Select * from table t1 join table t2 on t1.MainID = t2.ParentID

Difference between Strong and Weak in iOS

Ans : 

Strong

A strong property means that you want to “own” the object. Only when you set the property to nil will the object be  destroyed. Unless one or more objects also have a strong reference to the object. This is the one you will use in most cases.

1. Creates ownership between property and assigned value.

1. This is default for object property in ARC so it does not let you worrying about reference count and release the reference automatically.

1. It is replacement for retain. We use if and only if we need to use as retain.

1. Retain count will be incremented.

1. Creates non-ownerships between property and assigned value.

1. Strong is used on parent object and weak is used on child object when parent is released then child object reference is also set to nil

1. It helps to prevents retain cycles.

1. It doesn’t protect the referenced object when collection by garbage collector.

1. Weak is essentially assigned, un-retain property.

1. Retain count will not be incremented.

Weak

Weak property means you don’t want to have control over the objects lifecycle. The object only lives on while another objects has a strong reference to it. If there are no strong references to the object then it will be destroyed. 

Weak reference is useful to avoid situation like retain cycle. Retain cycle occurs when two or more objects have strong reference to each other. This two object will never be freed in memory due to strong reference. So to avoid weak reference, One object has a strong ownership reference to another object, and another object should be have a weak reference to first object.

Strong references should be used when a parent object is referencing a child object and never the other way around. That is, a child class should not have a strong reference to the parent class.

Weak references should be used to avoid retain cycles and an object has the possibility to become nil at any point of it’s lifetime.

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