Hi ,
Today I am going to share another demo in Android architecture series i.e. View Model . Firstly let me explain a short introduction of View Model:
So as I previously said, View Model is used to retain the data of configuration changes. So here I am going to explain a demo code , to check that View Model is really helpful to retain data while configuration changes (switching between landscape and portrait mode) or not .
In my demo code , I am taking one integer array , and getting one random number from that array .That random number will show on text-view. I will take 2 text-views , to hold the random number fetching from integer array. Among these two text-views , one will show the number normally while configuration changes and other text-view will show the number using view-model.So let's start:
-> Firstly I am adding following dependencies in build.gradle(app) file :
-> Before moving to activity java class, I have sub-classed , ViewModel class , with name :
RandomNumViewModel.java , please take a look on code:
Today I am going to share another demo in Android architecture series i.e. View Model . Firstly let me explain a short introduction of View Model:
- Survives Configuration changes i.e. Screen-rotation
- Not same as onSaveInstanceState (it is used to store small amount of data)
- View Model used for large data such as :Bitmap or user list
- store and manage UI related data
- Destroyed only if the user activity is completely destroyed, in onCleared()
- Communication layer between DB and UI
For more understanding , please refer : Android Developer View Model
So as I previously said, View Model is used to retain the data of configuration changes. So here I am going to explain a demo code , to check that View Model is really helpful to retain data while configuration changes (switching between landscape and portrait mode) or not .
In my demo code , I am taking one integer array , and getting one random number from that array .That random number will show on text-view. I will take 2 text-views , to hold the random number fetching from integer array. Among these two text-views , one will show the number normally while configuration changes and other text-view will show the number using view-model.So let's start:
-> Firstly I am adding following dependencies in build.gradle(app) file :
implementation "android.arch.lifecycle:runtime:1.1.1"
implementation "android.arch.lifecycle:extensions:1.1.1"
annotationProcessor "android.arch.lifecycle:compiler:1.1.1"
-> Take one layout named : view_model_layout.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="@+id/textview7"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:textSize="25sp"
android:textColor="#085937"
android:textStyle="bold"
android:text="TextView" />
<TextView
android:id="@+id/textview8"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/textview7"
android:layout_centerHorizontal="true"
android:layout_marginTop="30dp"
android:textSize="25sp"
android:textColor="#085937"
android:textStyle="bold"
android:text="TextView" />
</RelativeLayout>
-> Before moving to activity java class, I have sub-classed , ViewModel class , with name :
RandomNumViewModel.java , please take a look on code:
package com.development.view_model;
import android.arch.lifecycle.ViewModel;
import java.util.Random;
public class RandomNumViewModel extends ViewModel {
private int[] items = new int[]{1, 2, 3, 44, 65, 87, 22, 65, 87, 22, 90, 63, 4, 8, 50};
private Random random = new Random();
/**
* mRandomNumber , this variable should retain its value,
* on configuration change
*/
private int mRandomNumber = 0;
/**
* used to create a random number from array
* @return
*/
public int createNumber(){
mRandomNumber = items[random.nextInt(items.length)];
return mRandomNumber;
}
/**
* used to get the random number
* @return
*/
public int getRandArrayElement(){
if(mRandomNumber == 0){
mRandomNumber = createNumber();
return mRandomNumber;
}else{
return mRandomNumber;
}
}
}
-> Now take a look on my java file , I have named it as : ViewModelActivity.java
import android.arch.lifecycle.ViewModel;
import java.util.Random;
public class RandomNumViewModel extends ViewModel {
private int[] items = new int[]{1, 2, 3, 44, 65, 87, 22, 65, 87, 22, 90, 63, 4, 8, 50};
private Random random = new Random();
/**
* mRandomNumber , this variable should retain its value,
* on configuration change
*/
private int mRandomNumber = 0;
/**
* used to create a random number from array
* @return
*/
public int createNumber(){
mRandomNumber = items[random.nextInt(items.length)];
return mRandomNumber;
}
/**
* used to get the random number
* @return
*/
public int getRandArrayElement(){
if(mRandomNumber == 0){
mRandomNumber = createNumber();
return mRandomNumber;
}else{
return mRandomNumber;
}
}
}
-> Now take a look on my java file , I have named it as : ViewModelActivity.java
package com.development.view_model;
import android.arch.lifecycle.ViewModelProviders;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.widget.TextView;
import com.development.R;
import java.util.Random;
public class ViewModelActivity extends AppCompatActivity {
TextView txt,txt1;
private int[] items = new int[]{1, 2, 3, 44, 65, 87, 22, 65, 87, 22, 90, 63, 4, 8, 50};
private Random random = new Random();
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.view_model_layout);
txt = (TextView)findViewById(R.id.textview7);
txt1 = (TextView)findViewById(R.id.textview8);
int num = getRandArrayElement();
/**
* it's value should change on configuration change
*/
txt.setText(""+num); // normal way to set data on textview
/**
* Setting textview using View Model
* it's value should retain on configuration change
*/
RandomNumViewModel randomNumViewModel =
ViewModelProviders.of(this).get(RandomNumViewModel.class);
int num1 = randomNumViewModel.getRandArrayElement();
txt1.setText(""+num1);
}
public int getRandArrayElement(){
return items[random.nextInt(items.length)];
}
}
That's it , build and run the code, you can check that the value of one text-view will change , but value of another text-view will not change , while configuration changes (switching between landscape and portrait mode) , I have run my code , you can check the screen shots for various steps of screen-rotation:
import android.arch.lifecycle.ViewModelProviders;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.widget.TextView;
import com.development.R;
import java.util.Random;
public class ViewModelActivity extends AppCompatActivity {
TextView txt,txt1;
private int[] items = new int[]{1, 2, 3, 44, 65, 87, 22, 65, 87, 22, 90, 63, 4, 8, 50};
private Random random = new Random();
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.view_model_layout);
txt = (TextView)findViewById(R.id.textview7);
txt1 = (TextView)findViewById(R.id.textview8);
int num = getRandArrayElement();
/**
* it's value should change on configuration change
*/
txt.setText(""+num); // normal way to set data on textview
/**
* Setting textview using View Model
* it's value should retain on configuration change
*/
RandomNumViewModel randomNumViewModel =
ViewModelProviders.of(this).get(RandomNumViewModel.class);
int num1 = randomNumViewModel.getRandArrayElement();
txt1.setText(""+num1);
}
public int getRandArrayElement(){
return items[random.nextInt(items.length)];
}
}
Portrait Mode
Landscape Mode
Here in above screenshots, we can clearly see , that the second text-view , which is using View-Model , to show (retain) the number value , doesn't change while screen-rotation , but the first one changes its value.
