Introduction

I want to fold and stretch the contents of the recyclerview!

References

I referred to this. https://github.com/thoughtbot/expandable-recycler-view This one is easier to understand! !!

Implementation

First, add the build.gradle library.

`build.gradle`


dependencies {
    compile 'com.thoughtbot:expandablerecyclerview:1.3'
    compile 'com.android.support:recyclerview-v7:25.3.1'
}

Next, create a parent-only `ViewHolder``` and a child-only `ViewHolder```. ViewHolder makes the data and the View displayed on the screen related. Of course, since there are a parent view and a child view, two ViewHolders are required.

`Parent_ViewHolder.java`


package This is my package
import android.view.View;
import android.widget.TextView;

import com.thoughtbot.expandablerecyclerview.viewholders.GroupViewHolder;

public class Parent_ViewHolder extends GroupViewHolder {

    private TextView text1;

    public Parent_ViewHolder(View itemView) {//Get id of parent view
        super(itemView);
        text1 = (TextView)itemView.findViewById(R.id.parenttext);
    }
    public void set(String i){//Change the acquired id
        text1.setText(i);
    }
}

`Child_ViewHolder.java`


package This is my package;

import android.view.View;
import android.widget.TextView;

import com.thoughtbot.expandablerecyclerview.viewholders.ChildViewHolder;

public class Child_ViewHolder extends ChildViewHolder {

    private TextView text1;

    public Child_ViewHolder(View itemView) {//Get id of child view
        super(itemView);
        text1 = (TextView)itemView.findViewById(R.id.childtext);
    }
    public void set(String i){//Change the acquired id
        text1.setText(i);
    }
}

Then, we will create an adapter that associates these. Is it a place where parents and children are related, that is, like a home? : raised_hand:

`Home_Adapter.java`


package This is my package;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import com.thoughtbot.expandablerecyclerview.ExpandCollapseController;
import com.thoughtbot.expandablerecyclerview.ExpandableRecyclerViewAdapter;
import com.thoughtbot.expandablerecyclerview.models.ExpandableGroup;

import java.util.List;

public class Home_Adapter extends ExpandableRecyclerViewAdapter<Parent_ViewHolder, Child_ViewHolder> {

    private ExpandCollapseController expandCollapseController;

    public Home_Adapter(List<? extends ExpandableGroup> groups) {
        super(groups);
        this.expandCollapseController = new ExpandCollapseController(expandableList, this);
    }

    @Override
    public Parent_ViewHolder onCreateGroupViewHolder(final ViewGroup parent, final int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.parent_item, parent, false);
        return new Parent_ViewHolder(view);
    }

    @Override
    public Child_ViewHolder onCreateChildViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.child_item, parent, false);
        return new Child_ViewHolder(view);
    }

    @Override
    public void onBindGroupViewHolder(Parent_ViewHolder holder, int flatPosition, ExpandableGroup group) {
        holder.set(String.valueOf(flatPosition));//Parent_Call the function created by viewHolder
    }

    @Override
    public void onBindChildViewHolder(Child_ViewHolder holder, int flatPosition, ExpandableGroup group, int childIndex) {
        holder.set(String.valueOf(childIndex));//Child_Call the function created by viewHolder
    }

}

onCreateViewHolder Extends the contents of the specified xml file for the specified view.
onBindViewHolder Called by RecyclerView to display the data at the specified position.

Next, we will create a layout to be related.

`parent_item.xml`


<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">
    <TextView
        android:background="@color/colorPrimaryDark"
        android:id="@+id/parenttext"
        android:text="parent"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize" />
</LinearLayout>

`child_item.xml`


<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">
    <TextView
        android:id="@+id/childtext"
        android:text="Child"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize" />
</LinearLayout>

Next, now that the adapter and layout are complete, let's run it as a program. : point_up:

`MainActivity.java`


package jp.app.oomae.hisaki.expandable_recyclerview;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.DefaultItemAnimator;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.RecyclerView;

import static jp.app.oomae.hisaki.expandable_recyclerview.Home.makehome;

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.recyclerview);

        RecyclerView recyclerView = (RecyclerView)findViewById(R.id.recyclerview);
        recyclerView.setLayoutManager(new GridLayoutManager(this, 1));
        Home_Adapter adapter = new Home_Adapter(makehome());
        recyclerView.setAdapter(adapter);//Set the adapter
    }
}

And let's set up a recyclerview on the main screen.

`recyclerview.xml`


<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">
    <android.support.v7.widget.RecyclerView
        android:background="@color/colorAccent"
        android:id="@+id/recyclerview"
        android:scrollbars="vertical"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</LinearLayout>

Next, let's decide the number of parents and children to display. This time it is a static implementation, but if you change this, I think it will be dynamic. maybe,,, First, implement the parent and child data groups.

`Parent.java`


package my guy;
import com.thoughtbot.expandablerecyclerview.models.ExpandableGroup;
import java.util.List;

public class Parent extends ExpandableGroup<Child> {
    public Parent(String title, List<Child> items) {
        super(title, items);
    }
}

`Child.java`


package my guy;

import android.os.Parcel;
import android.os.Parcelable;

public class Child implements Parcelable {
    private String name;

    public Child(String name) {
        this.name = name;
    }

    protected Child(Parcel in) {
        name = in.readString();
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeString(name);
    }

    @Override
    public int describeContents() {
        return 0;
    }

    public static final Creator<Child> CREATOR = new Creator<Child>() {
        @Override
        public Child createFromParcel(Parcel in) {
            return new Child(in);
        }

        @Override
        public Child[] newArray(int size) {
            return new Child[size];
        }
    };
}

Next, let's create a house that associates `Parent.java``` with `Child.java```. (There can be no house with multiple parents and multiple children, but it feels like an accommodation ??)

`Home.java`


package jp.app.oomae.hisaki.expandable_recyclerview;

import java.util.Arrays;
import java.util.List;

public class Home{
    final private static int parents_num = 9;//Number of parents
    final private static int child_num = 5;//Number of children

    public static List<Parent> makehome() {
        Parent[] num = new Parent[parents_num];
        for(int i = 0; i < parents_num; i++) {
            num[i] = new Parent("parent" + String.valueOf(i),receive_child());
        }
        return Arrays.asList(num);
    }

    public static List<Child> receive_child() {
        Child[] num = new Child[child_num];
        for(int i = 0; i < child_num; i++) {
            num[i] = new Child("child" + String.valueOf(i));
        }
        return Arrays.asList(num);
    }
}

Here we combine the child data and the parent data.

That's all the code. We are looking for criticisms and criticisms. : muscle_tone3:

This code

https://github.com/hisakioomae/Expandable_Recyclerview_sample/tree/master

Folding and unfolding the contents of the Recyclerview

Introduction

References

Implementation

build.gradle

Parent_ViewHolder.java

Child_ViewHolder.java

Home_Adapter.java

parent_item.xml

child_item.xml

MainActivity.java

recyclerview.xml

Parent.java

Child.java

Home.java