[Android]  FragmentからActivityへ画面遷移＋Toolbarに戻るボタン表示の実装メモ

Tab上のFragmentでボタンを押す、Activityを表示する簡単な画面を実装しました。
また、遷移後の画面ではToolbarに戻るボタンが表示されます。

TAB02とTAB03の画面は載せていませんが、TAB01と同じようなFragmentとlayoutを増やしているだけです。
まだ勉強中なので、おかしい部分があるかもしれません。。

#作ったもの
※注意：ボタンテキストは「ToFragment」ではなく「ToActivity」でした…。
<img width="470" alt="スクリーンショット 2019-02-09 16.02.05.png" src="https://qiita-image-store.s3.amazonaws.com/0/281645/c5991f80-d686-3fa0-976a-70ef102713a7.png">
Button押下後の画面
<img width="470" alt="スクリーンショット 2019-02-09 16.06.26.png" src="https://qiita-image-store.s3.amazonaws.com/0/281645/d626ae2a-e84c-43ad-86db-e5dc1647ca47.png">

#MainActivity.java
```java:MainActivity.java
public class MainActivity extends AppCompatActivity {

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

        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        OriginalFragmentPagerAdapter adapter = new OriginalFragmentPagerAdapter(getSupportFragmentManager());
        ViewPager viewPager = findViewById(R.id.viewPager);
        viewPager.setOffscreenPageLimit(3);
        viewPager.setAdapter(adapter);

        TabLayout tabLayout = findViewById(R.id.tabLayout);
        tabLayout.setupWithViewPager(viewPager);

    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {

        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

}
```

#Tab01Fragment.java
```java:Tab01Fragment.java
public class Tab01Fragment extends Fragment {

    public Tab01Fragment() {
        // Required empty public constructor
    }


    private int cnt = 0;

    public static Tab01Fragment newInstance(int count){
        //Fragment インスタンス化
        Tab01Fragment tab01Fragment = new Tab01Fragment();

        //Bundleにパラメータを設定
        Bundle args = new Bundle();
        args.putInt("Counter", count);
        tab01Fragment.setArguments(args);

        return tab01Fragment;
    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_tab01, container, false);
    }


    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

        Bundle args = getArguments();

        if(args != null){
            int count = args.getInt("Counter");
            cnt = count + 1;
        }

        Button appButton = view.findViewById(R.id.Button);
        appButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(getActivity(), AppComDetailsActivity.class);
                startActivity(intent);
            }
        });
    }
}
```

#Tab01NextActivity.java
```java:Tab01NextActivity.java
public class Tab01NextActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_tab01_next);

        // Backボタンを有効にする
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        getSupportActionBar().setHomeButtonEnabled(true);

    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {

        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        switch (item.getItemId()) {
            case android.R.id.home:
                finish();
            default:
                break;
        }

        return super.onOptionsItemSelected(item);
    }
}
```
#Layout / activity_main.xml
```xml:activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/main_content"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context=".MainActivity">

    <android.support.design.widget.AppBarLayout
        android:id="@+id/appbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:paddingTop="@dimen/appbar_padding_top"
        android:theme="@style/AppTheme.AppBarOverlay">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:layout_weight="1"
            android:background="?attr/colorPrimary"
            app:layout_scrollFlags="scroll|enterAlways"
            app:popupTheme="@style/AppTheme.PopupOverlay"
            app:title="@string/app_name">

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

    </android.support.design.widget.AppBarLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        app:layout_behavior="@string/appbar_scrolling_view_behavior">

        <android.support.design.widget.TabLayout
            android:id="@+id/tabLayout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content">

            <android.support.design.widget.TabItem
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="Left" />

            <android.support.design.widget.TabItem
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="Center" />

            <android.support.design.widget.TabItem
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="Right" />
        </android.support.design.widget.TabLayout>

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

        </android.support.v4.view.ViewPager>

    </LinearLayout>

</android.support.design.widget.CoordinatorLayout>
```
#Layout / fragment_tab01.xml
```xml:fragment_tab01.xml
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".Tab01Fragment">

    <android.support.constraint.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <Button
            android:id="@+id/Button"
            android:layout_width="211dp"
            android:layout_height="wrap_content"
            android:layout_marginStart="8dp"
            android:layout_marginTop="8dp"
            android:layout_marginEnd="8dp"
            android:layout_marginBottom="8dp"
            android:text="ToFragment"
            android:textAllCaps="false"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.503"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.393" />
    </android.support.constraint.ConstraintLayout>

    <!--</LinearLayout>-->

</FrameLayout>
```
#Layout / activity_tab01_next.xml
```xml:activity_tab01_next.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"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#876"
    tools:context=".Tab01NextActivity">

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="表示されたActivity"
        android:textSize="24sp"
        android:textStyle="bold"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.502"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.425" />

</android.support.constraint.ConstraintLayout>
```

#Menu / menu_main.xml
```xml:menu_main.xml
<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    tools:context=".MainActivity">
    <item
        android:id="@+id/action_settings"
        android:orderInCategory="100"
        android:title="@string/action_settings"
        app:showAsAction="never" />
</menu>
```
#OriginalFragmentPagerAdapter.java
```java:OriginalFragmentPagerAdapter.java
public class OriginalFragmentPagerAdapter extends FragmentPagerAdapter {

    private CharSequence[] tabTitles = {"Tab01", "Tab02", "Tab03"};

    public OriginalFragmentPagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public CharSequence getPageTitle(int position) {
        return tabTitles[position];
    }

    @Override
    public Fragment getItem(int position) {
        switch (position) {
            case 0:
                return new Tab01Fragment();
            case 1:
                return new TabSystemFragment();
            case 2:
                return new TabAbnormalFragment();
            default:
                return null;
        }
    }

    @Override
    public int getCount() {
        return tabTitles.length;
    }
}
```

#Value / strings.xml
```xml:strings.xml
<resources>
    <string name="app_name">SampleApp</string>
    <string name="action_settings">Settings</string>
    <string name="section_format">Hello World from section: %1$d</string>

    <!-- TODO: Remove or change this placeholder text -->
    <string name="hello_blank_fragment">Hello blank fragment</string>

    <string name="appcount_label">Packages found</string>

</resources>
```

おわり！