Content Providers - Consuming data from a Content Provider using Content Resolver

-

Content Providers are used to share data between applications

When is it necessary to implement Content Provider?

  • When we have to expose our apps data with other app
  • Need some complex data copy functionality from our app
  • We intend to use : 
    Cursor Loader
    Cursor Adapter
    AbstractThreadedSyncAdapter
What kind of data can Content Provider Expose?
Data from Database
FIle Data(JSON, XML, Audio, Video, Photos)
Networked Data - AbstractThreadedSyncAdapter

How to implement Content Provider?
We need to make sure we have primary keys defined in our tables else Content Providers will not work properly
Implement Custom ContentProvider class
Define proper Content URIs for data to be exposed

Content URI?
Is an important concept to access any data from a ContentProvider. 
Assuming we are sharing data from database :
Content URI has 3 components :
Content : content://
Authority : Package Name of the App
Path : User Defined String Constants




Suppose App2 needs some data from App1
App2 will use an API called ContentResolver(Data Request) using which we will hit App1 database and the content provider defined in App1 will respond back using the format called Cursor(Data Resposne).
Cursor is an API which allows us to traverse through those rows defined in that particular tabular format data. Its a reference which we want to iterate over a table with multiple no of rows.
It is Inter Process Communication(IPC). What content provider does is it provides a kind of abstraction from handling this IPC.
Eg : In real world scenario, we have the Contacts App(APP1) and WhatsApp(APP2). It doesn't matter how the data is stored in Contacts App, it may be in JSON file, DB, File or XML. As long as content provider exposes that data, APP2 should be able to parse through the data being returned from the content provider defined in Contacts App.
The Context object contains a method called getContentResolver() which returns the instance of a Content Resolver. To hit the correct Content Provider, we should know the Uniform Resource Identifier(URI). URI is something like a URL which we use to hit a website.
URI will be unique to that Content Provider. The Content Resolver provides us certain methods using which we can perform CRUD & Batch operations.

Usual SQL Statement :
    SELECT col1, col2 FROM table_name WHERE col1 = value ORDER BY col2
Equivalent Query Method :
    getContentResolver().query(<ContentProvider>.Content_Uri, mProjection, mSelectionClause, mSelectionArgs, mSortOrder)
<ContentProvider>.CONTENT_URI : Most of the content providers are defined under android.provider package.
mProjection : Nothing but the number of columns that we want to query from table which is nothing but the string array representing the names of column which we need to query from content provider 
mSelectionClause : Equivalent to WHERE clause. Its a String datatype. 
mSelectionArgs : If we want to pass any arguments during runtime 
mSortOrder : The order in which the query need to be sorted

Comments

Post a Comment

Popular posts from this blog

Android - Using KeyStore to encrypt and decrypt the data

-
import android.content.Context; import android.os.Build; import android.security.keystore.KeyGenParameterSpec; import android.security.keystore.KeyProperties; import android.support.annotation. RequiresApi ; import android.util.Base64; import java.io.UnsupportedEncodingException; import java.security.InvalidAlgorithmParameterException; import java.security.InvalidKeyException; import java.security.KeyStore; import java.security.KeyStoreException; import java.security.NoSuchAlgorithmException; import java.security.NoSuchProviderException; import java.security.UnrecoverableKeyException; import javax.crypto.BadPaddingException; import javax.crypto.Cipher; import javax.crypto.IllegalBlockSizeException; import javax.crypto.KeyGenerator; import javax.crypto.NoSuchPaddingException; import javax.crypto.SecretKey; import javax.crypto.spec.GCMParameterSpec; public class KeyStoreUtil { private static final String FIXED_IV = "467096543987" ; KeyStore keyStore ; Contex...
Read more

Stack and Queue

-
Image
  What is Stack? Stack is a linear data structure that follows the specific order to perform the operations. For example, if we want to access the element in the array we can do it any time but in the case of stack data structure, there is only one sequence to access the element. In the stack, we insert the element from one end with push operation and delete the element from the same end using pop operation. The end of the stack used to perform all the operations is called the top of the stack. Therefore, a stack follows the LIFO (Last In First Out) principle, which means the element that is inserted last will be the first element to come out of the stack. The most important thing to remember in the stack data structure is that it stores the elements of the same data type only.     Let us understand the condition to check whether the stack is empty for full: Condition to Check if Stack is Empty int Empty() { if (top ==- 1 ) return 1 ; else return 0 ; }   Con...
Read more

Java Reflection API

-
Java Reflection  is a process of examining or modifying the run time behavior of a class at run time The  java.lang.Class  class provides many methods that can be used to get metadata, examine and change the run time behavior of a class. The java.lang and java.lang.reflect packages provide classes for java reflection The java.lang.Class class performs mainly two tasks: provides methods to get the metadata of a class at run time. provides methods to examine and change the run time behavior of a class. How to get the object of Class class? There are 3 ways to get the instance of Class class. They are as follows: forName() method of Class class getClass() method of Object class the .class syntax 1) forName() method of Class class is used to load the class dynamically. returns the instance of Class class. It should be used if you know the fully qualified name of class.This cannot be used for primitive types. Let's see the simple example of forName() meth...
Read more