• Chapter 8: Intents
• Chapter 9: Fragments
• Chapter 10: Navigation
• Chapter 16: Jetpack, LiveData, ViewModel, and Room

• 23-24. Managing Constraints using Constraint Sets -- UI by Java, skip
• 27-29. Android Touch and Multi-touch Event Handling -- good, have to skip
• *30-31. An Introduction to Android Fragments
• 32-39. Modern Android App Architecture with Jetpack
• *40-41. An Overview of the Navigation Architecture Component
• 46. Creating a Tabbed Interface using the TabLayout Component -- cover partially
• *47-48. Working with the RecyclerView and CardView Widgets
• *47-50. Working with the RecyclerView and CardView Widgets
• *52-53. An Overview of Android Intents
• 56. A Basic Overview of Java Threads, Handlers and Executors
• More ...

• RecyclerView -- list representation for data or navigation, #1 nav
• Intent -- multiple screens, overkill
• ViewPager2 + Tabbed -- #2 nav
• Fragment -- multiple
• Navigation -- #3 nav
• Bluetooth and Services
• More ...

<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
...
    <TextView
        android:id="@+id/vv_tvTitle"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/rc_strTitle"
...

    <androidx.recyclerview.widget.RecyclerView	##### RecyclerView
        android:id="@+id/vv_rvList"
        android:layout_width="wrap_content"
...

	<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
...
	    <TextView
        android:id="@+id/vv_tvCell"	##### RecyclerView List Cell, just a textView now
...
	

public class MainActivity extends AppCompatActivity {
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		...
		RecyclerView lv_recyclerView = findViewById(R.id.vv_rvList);
		// ##### small issue
		lv_recyclerView.setLayoutManager(new LinearLayoutManager(this));
		String[] lv_data = new String[32];
		for (int i = 0; i < 32; i++) {
			lv_data[i] = i+"th Element";
		}
		// #### major issue -- NEED an Adapter (user defined) together
		lv_recyclerView.setAdapter(new MyRecyclerViewAdapter(lv_data));
	}
}
	

// https://www.willowtreeapps.com/craft/android-fundamentals-working-with-the-recyclerview-adapter-and-viewholder-pattern

// ##### need 2 -- Adapter and ViewHolder 
public class MyRecyclerViewAdapter extends RecyclerView.Adapter<MyRecyclerViewAdapter.MyViewHolder> {
    private final String[] mv_data;

    // ##### ViewHolder as static inner class (subclass)
    public static class MyViewHolder extends RecyclerView.ViewHolder {
        private final TextView cv_tvCell;
        public MyViewHolder(View view) {
            super(view);
            // (1)##### binding between Adapter variable and XML layout widgets #####	
            cv_tvCell = view.findViewById(R.id.vv_tvCell);
        }
    }


    // ##### customized constructor, more info in future
    public MyRecyclerViewAdapter(String[] data) {
        mv_data = data;
    }

    // ##### connection between Adapter and ViewHolder
    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        // (2)##### A new view which defines the list cell UI
		View lv_view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.recyclerview_row, parent, false);
        return new MyViewHolder(lv_view);
    }

    // ##### Replace the contents of a view (invoked by the layout manager)
    @Override
    public void onBindViewHolder(MyRecyclerViewAdapter.MyViewHolder holder, int position) {
        // (3)##### draw list cell by data(index) #####
        holder.cv_tvCell.setText(mv_data[position]);
    }

    // ##### MUST, Return the size of your dataset (invoked by the layout manager)
    @Override
    public int getItemCount() {
        return mv_data.length;
    }
}

• 2 Layout -- 1.main, 2.list cell
• 2 Java -- 1.main, 2. adapter
• Adapter works with 1.data(passed from main), 2.holder (as inner class)
• Adapter associates 1.list cell xml with 2.ViewHolder in @override onCreateViewHolder
• ViewHolder update list cell in @override onBindViewHolder()

• Layout background color
• TextView Font Size to 24sp
• Create margin to separate cells

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="46sp"	
    android:layout_margin="8dp"				##### here
    android:background="@color/purple_200">		##### here

    <TextView
        android:id="@+id/vv_tvCell"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/app_name"
        android:textSize="24sp" />			##### here

</LinearLayout>

• 1.MyViewHolder(View view)
• 2.onCreateViewHolder(ViewGroup parent, int viewType)
• 3.onBindViewHolder(MyViewHolder holder, int position)

In a nutshell, The Activity class will implement an interface for onClick event, 
this interface will be passed to the RecyclerView Adapter class, then the ViewHolder class
in the RecyclerView will call onClick method defined in the interface, which will pass the
view and position of the clicked item to the onClick implementation in the Activity class.

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import android.widget.Toast;
import androidx.recyclerview.widget.RecyclerView;

public class MyRecyclerViewAdapter extends RecyclerView.Adapter<MyRecyclerViewAdapter.MyViewHolder> {
    private final String[] mv_data;

    public static class MyViewHolder extends RecyclerView.ViewHolder {
        private final TextView cv_tvCell;

        public MyViewHolder(View view) {
            super(view);
            // Define click listener for the ViewHolder's View
            cv_tvCell = view.findViewById(R.id.vv_tvCell);
//// Method 1:
/*            view.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    Toast.makeText(view.getContext(), "position : " + getLayoutPosition()
                            + " text : " + cv_tvCell.getText(), Toast.LENGTH_SHORT).show();
                }
            });*/
        }
    }

    public MyRecyclerViewAdapter(String[] data) {
        mv_data = data;
    }

    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        // Create a new view, which defines the UI of the list item
        View lv_view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.recyclerview_row, parent, false);
        return new MyViewHolder(lv_view);

//// Method 2: BETTER then Method 3?
/*        MyViewHolder lv_holder = new MyViewHolder(lv_view);
        lv_view.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Toast.makeText(view.getContext(), "position : " + lv_holder.getLayoutPosition()
                        + " text : " + lv_holder.cv_tvCell.getText(), Toast.LENGTH_SHORT).show();
            }
        });
        return lv_holder;*/
    }

    // Replace the contents of a view (invoked by the layout manager)
    @Override
    public void onBindViewHolder(MyRecyclerViewAdapter.MyViewHolder holder, int position) {
        holder.cv_tvCell.setText(mv_data[position]);

//// Method 3: itemView is hidden defined
        holder.itemView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    Toast.makeText(view.getContext(), "position : " + holder.getLayoutPosition()
                            + " text : " + holder.cv_tvCell.getText(), Toast.LENGTH_SHORT).show();
                }
            });
    }

    // Return the size of your dataset (invoked by the layout manager)
    @Override
    public int getItemCount() {
        return mv_data.length;
    }
}

• Change data from String[] to ArrayList (for easy insert/delete)
• FAB click and long click to add/remove items

public class MainActivity extends AppCompatActivity {
    //// HERE
    ArrayList lv_data;
    MyRecyclerViewAdapter lv_adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
		...
        //// HERE
        lv_data = new ArrayList<>();
        for (int i = 0; i < 32; i++) {
            lv_data.add(i+"th Element");
        }
        lv_adapter = new MyRecyclerViewAdapter(lv_data);
        lv_recyclerView.setAdapter(lv_adapter);

		...
        fab.setOnLongClickListener(new View.OnLongClickListener() {
            @Override
            public boolean onLongClick(View view) {
                //lv_data.add(1, "New Item");
                lv_data.remove(2);
                lv_adapter.notifyDataSetChanged();
                return true;
            }
        });
    }

• Chanage data to ArrayList type
• Modify accordingly

public class MyRecyclerViewAdapter extends RecyclerView.Adapter<MyRecyclerViewAdapter.MyViewHolder> {
    //// HERE
    private final ArrayList<String> mv_data;

    //// HERE
    public MyRecyclerViewAdapter(ArrayList<String> data) {
        mv_data = data;
    }

    @Override
    public void onBindViewHolder(MyRecyclerViewAdapter.MyViewHolder holder, int position) {
        //// HERE
        holder.cv_tvCell.setText(mv_data.get(position));
	...
    }

	...
    @Override
    public int getItemCount() {
        //// HERE
        return mv_data.size();
    }

• Add TextView vv_tvModel
• Add TextView vv_tvPrice
• Add TextView vv_tvOS
• Alignment them

• Two ArrayLists for data
• Data defined in String[] then to ArrayList
• DividerItemDecoration.VERTICAL

public class MainActivity extends AppCompatActivity {
    //// HERE
    ArrayList lv_data01, lv_data02;
	...
    @Override
    protected void onCreate(Bundle savedInstanceState) {
	...
        //// HERE
        String[] lv_Model = {"iPad","Xoom","Playbook","TouchPad","Surface"};
        String[] lv_OS = {"iOS","Android","BlackBerry","WebOS","Windows"};

        lv_data01 = new ArrayList<>();
        lv_data02 = new ArrayList<>();
        Collections.addAll(lv_data01, lv_Model);
        Collections.addAll(lv_data02, lv_OS);

        lv_adapter = new MyRecyclerViewAdapter(lv_data01, lv_data02);
        lv_recyclerView.setAdapter(lv_adapter);
        lv_recyclerView.addItemDecoration(new DividerItemDecoration(this, DividerItemDecoration.VERTICAL));

	...
        fab.setOnLongClickListener(new View.OnLongClickListener() {
            @Override
            public boolean onLongClick(View view) {
                //// HERE
                lv_data01.remove(2);
                lv_data02.remove(2);
                lv_adapter.notifyDataSetChanged();
                return true;
            }
        });
    }

• Two ArrayLists data
• Three TextViews cv_tvModel, cv_tvOS, cv_tvPrice
• Accoringly

public class MyRecyclerViewAdapter extends RecyclerView.Adapter<MyRecyclerViewAdapter.MyViewHolder> {
    //// HERE
    private final ArrayList<String> mv_data01, mv_data02;

    public static class MyViewHolder extends RecyclerView.ViewHolder {
        //// HERE
        private final TextView cv_tvModel, cv_tvOS, cv_tvPrice;

        public MyViewHolder(View view) {
            super(view);
            // Define click listener for the ViewHolder's View
			//// MODIFY HERE
        }
    }
	//// MODIFY HERE
    public MyRecyclerViewAdapter(...
    }
	...
    @Override
    public void onBindViewHolder(MyRecyclerViewAdapter.MyViewHolder holder, int position) {
	//// MODIFY HERE
	//// including click
    }
    @Override
    public int getItemCount() {
	//// MODIFY HERE
    }

• Very effective (Mac Dock)
• Too much iOS (one of the two iOS primary navations)
• iPhone dial etc.
• Android 'borrow' then 'pride' won't allow, but still a lot use now

• Android Answer to Bottom Tab
• Primitive look, need heavy customization
• Combined with ViewPager

• Swipe left right
• Combined with ViewPager
• Tab + ViewPager is one of the primary Android Nav

• Too much iOS (one of the two iOS primary navations)
• iPhone mail etc.
• Android 'borrow' then 'pride' won't allow, but still a lot use now
• Android 'improves' to primary/detail flow

• Android Answer to List
• Hamburger button -- some likes it, some hates it
• However, it becomes so popular -- now iOS and Windows adopt it
• Both hamburger button and left-right edge swipe will bring out the side menu

• Intent
• Fragment

• Hard code in Java -- Interface Bulder (IB)
• Jetpack Navigation -- Storyboard

• Screen 1 has a textview and a button
• Button click will enter 2nd screen, then nothing
• Navigation back button (at the bottom) returns 1st screen

• vv_tvOut1
• vv_btnTo2

• Right Click Java -> New -> Activity -> Empty Activity
  
• Android Studio automatically generates Java+XML

• Leave it now
• Or change background color

• Leave it now

import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;

import com.example.a11_intent.databinding.ActivityMainBinding;
public class MainActivity extends AppCompatActivity {
    private ActivityMainBinding binding;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //setContentView(R.layout.activity_main);
        binding = ActivityMainBinding.inflate(getLayoutInflater());
        setContentView(binding.getRoot());

        binding.vvBtnTo2.setOnClickListener(
                new View.OnClickListener() {
                    @Override
                    public void onClick(View view) {
                        ////Context ctx =  MainActivity.this;
                        // need MainActivity.this since 'this' is new OnclickListener
                        Intent lv_it = new Intent(MainActivity.this, MySecondActivity.class);
                        startActivity(lv_it);
                    }
                });
    }
}

• Add a button vv_btnTo1
• Center it

• 1.Toolbar button at the top
• 2.Button
• 3.Navigation button at the buttom