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Lesson 4

Android Developer Fundamentals V2

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User Interaction

Android Developer Fundamentals V2

RecyclerView

This work is licensed under a Creative Commons Attribution 4.0 International License.

Android Developer Fundamentals V2

RecyclerView

This work is licensed under a Creative Commons Attribution 4.0 International License.

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4.4 RecyclerView

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Android Developer Fundamentals V2

RecyclerView

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Contents

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  • RecyclerView Components
  • Implementing a RecyclerView

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Android Developer Fundamentals V2

RecyclerView

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What is a RecyclerView?

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  • RecyclerView is scrollable container for large data sets
  • Efficient
    • Uses and reuses limited number of View elements
    • Updates changing data fast

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Android Developer Fundamentals V2

RecyclerView

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RecyclerView Components

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Android Developer Fundamentals V2

RecyclerView

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Components

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Overview

  • Data
  • RecyclerView scrolling list for list items—RecyclerView
  • Layout for one item of data—XML file
  • Layout manager handles the organization of UI components in a View—Recyclerview.LayoutManager
  • Adapter connects data to the RecyclerView—RecyclerView.Adapter
  • ViewHolder has view information for displaying one item—RecyclerView.ViewHolder

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Android Developer Fundamentals V2

RecyclerView

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Components

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How components fit together overview

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Android Developer Fundamentals V2

RecyclerView

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Layout Manager

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What is a layout manager?

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Android Developer Fundamentals V2

RecyclerView

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Adapter

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What is an adapter?

  • Helps incompatible interfaces work together
    • Example: Takes data from database Cursor and prepares strings to put into a View
  • Intermediary between data and View
  • Manages creating, updating, adding, deleting View items as underlying data changes
  • RecyclerView.Adapter

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Android Developer Fundamentals V2

RecyclerView

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Adapter

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What is a ViewHolder?

  • Used by the adapter to prepare one View with data for one list item
  • Layout specified in an XML resource file
  • Can have clickable elements
  • Is placed by the layout manager
  • RecyclerView.ViewHolder

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Android Developer Fundamentals V2

RecyclerView

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Implementing RecyclerView

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Android Developer Fundamentals V2

RecyclerView

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Implementation

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Steps Summary

  1. Add RecyclerView dependency to build.gradle if needed
  2. Add RecyclerView to layout
  3. Create XML layout for item
  4. Extend RecyclerView.Adapter
  5. Extend RecyclerView.ViewHolder
  6. In Activity onCreate(), create RecyclerView with adapter and layout manager

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Android Developer Fundamentals V2

RecyclerView

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app/build.gradle

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Add dependency to app/build.gradle

Add RecyclerView dependency to build.gradle if needed:

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dependencies {

...

compile 'com.android.support:recyclerview-v7:26.1.0'

...

}

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Android Developer Fundamentals V2

RecyclerView

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Activity layout

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Add RecyclerView to XML Layout

<android.support.v7.widget.RecyclerView

android:id="@+id/recyclerview"

android:layout_width="match_parent"

android:layout_height="match_parent">

</android.support.v7.widget.RecyclerView>

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Android Developer Fundamentals V2

RecyclerView

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Item layout

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Create layout for 1 list item

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<LinearLayout …>

<TextView

android:id="@+id/word"

style="@style/word_title" />

</LinearLayout>

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Android Developer Fundamentals V2

RecyclerView

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Adapter: Create

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Implement the adapter

public class WordListAdapter

extends RecyclerView.Adapter<WordListAdapter.WordViewHolder> {

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public WordListAdapter(Context context,

LinkedList<String> wordList) {

mInflater = LayoutInflater.from(context);

this.mWordList = wordList;

}

}

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Android Developer Fundamentals V2

RecyclerView

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Adapter: onCreateViewHolder()

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Adapter has 3 required methods

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  • onCreateViewHolder()
  • inBindViewHolder()
  • getItemCount()

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Let's take a look!

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RecyclerView

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Adapter: onCreateViewHolder()

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onCreateViewHolder()

@Override

public WordViewHolder onCreateViewHolder(� ViewGroup parent, int viewType) {

// Create view from layout

View mItemView = mInflater.inflate(

R.layout.wordlist_item, parent, false);

return new WordViewHolder(mItemView, this);

}

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Android Developer Fundamentals V2

RecyclerView

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Adapter: onBindViewHolder()

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onBindViewHolder()

@Override

public void onBindViewHolder(� WordViewHolder holder, int position) {

// Retrieve the data for that position

String mCurrent = mWordList.get(position);

// Add the data to the view

holder.wordItemView.setText(mCurrent);

}

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Android Developer Fundamentals V2

RecyclerView

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Adapter: getItemCount()

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getItemCount()

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@Override

public int getItemCount() {

// Return the number of data items to display

return mWordList.size();

}

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Android Developer Fundamentals V2

RecyclerView

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Adapter: ViewHolder Class

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Create the view holder in adapter class

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class WordViewHolder extends RecyclerView.ViewHolder { //.. }

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If you want to handle mouse clicks:

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class WordViewHolder extends RecyclerView.ViewHolder

implements View.OnClickListener { //.. }

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Android Developer Fundamentals V2

RecyclerView

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ViewHolder: Constructor

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View holder constructor

public WordViewHolder(View itemView, WordListAdapter adapter) {

super(itemView);

// Get the layout

wordItemView = itemView.findViewById(R.id.word);

// Associate with this adapter

this.mAdapter = adapter;

// Add click listener, if desired

itemView.setOnClickListener(this);

}

// Implement onClick() if desired

​

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Android Developer Fundamentals V2

RecyclerView

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Create RecyclerView

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Create the RecyclerView in Activity onCreate()

mRecyclerView = findViewById(R.id.recyclerview);

mAdapter = new WordListAdapter(this, mWordList);

mRecyclerView.setAdapter(mAdapter);

mRecyclerView.setLayoutManager(new

LinearLayoutManager(this));

​

​

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Android Developer Fundamentals V2

RecyclerView

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Practical: RecyclerView

  • This is rather complex with many separate pieces. So, there is a whole practical where you implement a RecyclerView that displays a list of clickable words.

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  • Shows all the steps, one by one with a complete app

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Android Developer Fundamentals V2

RecyclerView

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Learn more

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Android Developer Fundamentals V2

RecyclerView

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What's Next?

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  • Concept Chapter: 4.5 RecyclerView
  • Practical: 4.5 RecyclerView

Android Developer Fundamentals V2

RecyclerView

This work is licensed under a Creative Commons Attribution 4.0 International License.

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END

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Android Developer Fundamentals V2