Passing Arguments in Android using Safe Args by Navigation Library

 Passing Arguments from Fragment to Fragment using Safe Args provided by Navigation 

Android Bundle 

• Fragments contain arguments in the form of an Android Bundle. 
• It is a Key Value store also known as dictionary or associative array. 
• Dictionary is a data structure where we use a unique key such as string to fetch an associated value. 
• There are limited types that can be stored as values in a bundle. Primitive types such as char, int and float along with various types of arrays, char sequence, and few data classes such as array list. 

Use Case :

• Declare the arguments and assign val 
• Pass the arguments to the fragments. 

argBundle = Bundle()
argBundle.putString(CoolConstants.ARGUMENTS_KEY_STRING, "Content")
argBundle.putInt(CoolConstants.ARGUMENTS_KEY_INT, 14)

val fragment = PlayFragment()
fragment.arguments = argBundle

This works but it can generate bugs likes : 

• Types : we have to make sure the types match 
• Getting an integer from a string within the bundle returns a default value of zero. 
• If we try to get an argument as a string that you haven't set in the bundle it will return null. 
• There is no way to guarantee that what you pass into fragment A is what recipient asks for on the other end. 

val name = arguments?.getString(CoolConstants.ARGUMENTS_KEY_STRING)

Safe Args

• Safe Args is a gradle plugin that generates code to helps guarantee that the arguments on both side match up. 
• It also simplifies argument passing. 

Use Case:

• Add the classpath for the navigation-safe-args-gradle-plugin into project Gradle file 
• Apply plugin to app Gradle file 

// safe args
def nav_version = "2.3.2"
classpath "androidx.navigation:navigation-safe-args-gradle-plugin:$nav_version"

apply plugin: "androidx.navigation.safeargs"

apply plugin: "androidx.navigation.safeargs"

id "androidx.navigation.safeargs"

view.findNavController().
navigate(PlayFragmentDirections.actionPlayFragmentToGamewonFragment(answer as String))

var args = arguments?.let { GamelostFragmentArgs.fromBundle(it) }
lost_answer.text = args?.answer?:""