Challenge: Adding First and Last Buttons

Android Programming (3rd Edition) 11. Using ViewPager
1

Here is my solution to the challenge including the bonus

CrimePagerActivity.java 
package com.bignerdranch.android.criminalintent;

import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentStatePagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;

import java.util.List;
import java.util.UUID;

public class CrimePagerActivity extends AppCompatActivity {
    private static final String EXTRA_CRIME_ID = "com.bignerdranch.android.criminalintent.crime_id";

    private ViewPager mViewPager;
    private List<Crime> mCrimes;
    private Button mFirstButton;
    private Button mLastButton;

    public static Intent newIntent(Context packageContext, UUID crimeId) {
        Intent intent = new Intent(packageContext, CrimePagerActivity.class);
        intent.putExtra(EXTRA_CRIME_ID, crimeId);
        return intent;
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_crime_pager);

        UUID crimeId = (UUID) getIntent().getSerializableExtra(EXTRA_CRIME_ID);

        mViewPager = (ViewPager) findViewById(R.id.crime_view_pager);
        mCrimes = CrimeLab.get(this).getCrimes();

        FragmentManager fragmentManager = getSupportFragmentManager();
        mViewPager.setAdapter(new FragmentStatePagerAdapter(fragmentManager) {

            @Override
            public Fragment getItem(int position) {
                Crime crime = mCrimes.get(position);
                return CrimeFragment.newInstace(crime.getID());
            }

            @Override
            public int getCount() {
                return mCrimes.size();
            }
        });

        for (int i = 0 ; i < mCrimes.size() ; i++) {
            if (mCrimes.get(i).getID().equals(crimeId)) {
                mViewPager.setCurrentItem(i);
                break;
            }
        }

        mViewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

                if (mViewPager.getCurrentItem() == 0) {
                    mFirstButton.setVisibility(View.INVISIBLE);
                } else {
                    mFirstButton.setVisibility(View.VISIBLE);
                }

                if (mViewPager.getCurrentItem() == mViewPager.getAdapter().getCount() - 1) {
                    mLastButton.setVisibility(View.INVISIBLE);
                } else {
                    mLastButton.setVisibility(View.VISIBLE);
                }
            }

            @Override
            public void onPageSelected(int position) {
            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });

        mFirstButton = (Button) findViewById(R.id.first_crime);
        mFirstButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                mViewPager.setCurrentItem(0);
            }
        });

        mLastButton = (Button) findViewById(R.id.last_crime);
        mLastButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                mViewPager.setCurrentItem(mViewPager.getAdapter().getCount() - 1);
            }
        });

    }
}
activity_crime_pager.xml 
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.v4.view.ViewPager
        android:id="@+id/crime_view_pager"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
    </android.support.v4.view.ViewPager>

    <Button
        android:id="@+id/first_crime"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|left"
        android:layout_margin="16dp"
        android:text="First"/>

    <Button
        android:id="@+id/last_crime"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|right"
        android:layout_margin="16dp"
        android:text="Last"/>

</FrameLayout>
1 Like
2

My solution where I removed all unchanged code. Check this solution ONLY if you stuck:

CrimePagerActivity.java 
CrimePagerActivity extends AppCompatActivity {
    ...
    private Button mFirstButton;
    private Button mLastButton;
    ...

    @Override
    public void onCreate(Bundle savedInstanceState) {
        ...
        mViewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {

            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
                // Do nothing
            }

            @Override
            public void onPageSelected(int position) {
                mFirstButton.setEnabled(position != 0);
                mLastButton.setEnabled(position != (mCrimes.size() - 1));
            }

            @Override
            public void onPageScrollStateChanged(int state) {
                // Do nothing
            }
        });

        mFirstButton = (Button) findViewById(R.id.first_crime);
        mFirstButton.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                mViewPager.setCurrentItem(0);
            }

        });

        mLastButton = (Button) findViewById(R.id.last_crime);
        mLastButton.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                mViewPager.setCurrentItem(mCrimes.size() - 1);
            }

        });
       ...
    }
}
activity_crime_pager.xml 
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <android.support.v4.view.ViewPager
        android:id="@+id/crime_view_pager"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintRight_toRightOf="parent"/>

    <android.support.constraint.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent">

        <Button
            android:id="@+id/first_crime"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_margin="16dp"
            android:text="First Crime"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintTop_toTopOf="parent"/>

        <Button
            android:id="@+id/last_crime"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_margin="16dp"
            android:text="Last Crime"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintBottom_toBottomOf="parent"/>

    </android.support.constraint.ConstraintLayout>
</android.support.constraint.ConstraintLayout>
1 Like
3

Hi,
I added some code to check if we’ve pages at all (we could have remove the last item’s)

…

        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
            if (mViewPager.getAdapter().getCount() == 0 || mViewPager.getCurrentItem() <= 0) {
                mFirstButton.setVisibility(View.INVISIBLE);
            } else {
                mFirstButton.setVisibility(View.VISIBLE);
            }

            if (mViewPager.getAdapter().getCount() == 0 || mViewPager.getCurrentItem() == mViewPager.getAdapter().getCount() - 1) {
                mLastButton.setVisibility(View.INVISIBLE);
            } else {
                mLastButton.setVisibility(View.VISIBLE);
            }

…