CrimeFragment is a controller that interacts with model and view objects. Its job is to present the details of a specific crime and update those details as the user changes them.

In GeoQuiz, your activities did most of their controller work in activity lifecycle methods. In CriminalIntent, this work will be done by fragments in fragment lifecycle methods. Many of these methods correspond to the Activity methods you already know, such as onCreate(Bundle).

In CrimeFragment.java, add a member variable for the Crime instance and an implementation of Fragment.onCreate(Bundle).

Android Studio can provide some assistance when overriding methods. As you define the onCreate(Bundle) method, type the first few characters of the method name where you want to place the method. Android Studio will provide a list of suggestions, as shown in Figure 7.16.

Figure 7.16  Overriding the onCreate(Bundle) method

Press Return to select the onCreate(Bundle) method, and Android Studio will create the method declaration for you. Update your code to create a new Crime, matching Listing 7.10.

public class CrimeFragment extends Fragment {
    private Crime mCrime;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mCrime = new Crime();
    }
}

There are a couple of things to notice in this implementation. First, Fragment.onCreate(Bundle) is a public method, whereas Activity.onCreate(Bundle) is protected. Fragment.onCreate(Bundle) and other Fragment lifecycle methods must be public, because they will be called by whatever activity is hosting the fragment.

Second, similar to an activity, a fragment has a bundle to which it saves and retrieves its state. You can override Fragment.onSaveInstanceState(Bundle) for your own purposes just as you can override Activity.onSaveInstanceState(Bundle).

Also, note what does not happen in Fragment.onCreate(Bundle): You do not inflate the fragment’s view. You configure the fragment instance in Fragment.onCreate(Bundle), but you create and configure the fragment’s view in another fragment lifecycle method:

    public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState)

This method is where you inflate the layout for the fragment’s view and return the inflated View to the hosting activity. The LayoutInflater and ViewGroup parameters are necessary to inflate the layout. The Bundle will contain data that this method can use to re-create the view from a saved state.

In CrimeFragment.java, add an implementation of onCreateView(…) that inflates fragment_crime.xml. You can use the same trick from Figure 7.16 to fill out the method declaration.

public class CrimeFragment extends Fragment {
    private Crime mCrime;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mCrime = new Crime();
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.fragment_crime, container, false);
        return v;
    }
}

Within onCreateView(…), you explicitly inflate the fragment’s view by calling LayoutInflater.inflate(…) and passing in the layout resource ID. The second parameter is your view’s parent, which is usually needed to configure the widgets properly. The third parameter tells the layout inflater whether to add the inflated view to the view’s parent. You pass in false because you will add the view in the activity’s code.

You are now going to hook up the EditText, Checkbox, and Button in your fragment. The onCreateView(…) method is the place to wire up these widgets.

Start with the EditText. After the view is inflated, get a reference to the EditText and add a listener.

public class CrimeFragment extends Fragment {
    private Crime mCrime;
    private EditText mTitleField;
    ...
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.fragment_crime, container, false);

        mTitleField = (EditText) v.findViewById(R.id.crime_title);
        mTitleField.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(
                CharSequence s, int start, int count, int after) {
                // This space intentionally left blank
            }

            @Override
            public void onTextChanged(
                CharSequence s, int start, int before, int count) {
                mCrime.setTitle(s.toString());
            }

            @Override
            public void afterTextChanged(Editable s) {
                // This one too
            }
        });

        return v;
    }
}

Getting references in Fragment.onCreateView(…) works nearly the same as in Activity.onCreate(Bundle). The only difference is that you call View.findViewById(int) on the fragment’s view. The Activity.findViewById(int) method that you used before is a convenience method that calls View.findViewById(int) behind the scenes. The Fragment class does not have a corresponding convenience method, so you have to call the real thing.

Setting listeners in a fragment works exactly the same as in an activity. In Listing 7.12, you create an anonymous class that implements the verbose TextWatcher interface. TextWatcher has three methods, but you only care about one: onTextChanged(…).

In onTextChanged(…), you call toString() on the CharSequence that is the user’s input. This method returns a string, which you then use to set the Crime’s title.

Next, connect the Button to display the date of the crime, as shown in Listing 7.13.

public class CrimeFragment extends Fragment {
    private Crime mCrime;
    private EditText mTitleField;
    private Button mDateButton;
    ...
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.fragment_crime, container, false);
        ...
        mDateButton = (Button) v.findViewById(R.id.crime_date);
        mDateButton.setText(mCrime.getDate().toString());
        mDateButton.setEnabled(false);

        return v;
    }
}

Disabling the button ensures that it will not respond in any way to the user pressing it. It also changes its appearance to advertise its disabled state. In Chapter 12, you will enable the button and allow the user to choose the date of the crime.

Moving on to the CheckBox, get a reference and set a listener that will update the mSolved field of the Crime, as shown in Listing 7.14.

public class CrimeFragment extends Fragment {
    private Crime mCrime;
    private EditText mTitleField;
    private Button mDateButton;
    private CheckBox mSolvedCheckBox;
    ...
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.fragment_crime, container, false);
        ...
        mSolvedCheckBox = (CheckBox)v.findViewById(R.id.crime_solved);
        mSolvedCheckBox.setOnCheckedChangeListener(new OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton buttonView,
                    boolean isChecked) {
                mCrime.setSolved(isChecked);
            }
        });

        return v;
    }
}

After typing in the code as above, click on OnCheckedChangeListener:

    mSolvedCheckBox.setOnCheckedChangeListener(new OnCheckedChangeListener()

and use the Option+Return (Alt+Enter) shortcut to add the necessary import statement. You will be presented with two options. Choose the android.widget.CompoundButton version.

Depending on which version of Android Studio you are using, the autocomplete feature may insert CompoundButton.OnCheckedChangeListener() instead of leaving the code as OnCheckedChangeListener(). Either implementation is fine. But to remain consistent with the solution presented in this book, click on CompoundButton and hit Option+Return (Alt+Enter).

Select the option to Add on demand static import for 'android.widget.CompoundButton' (Figure 7.17). This will update the code so it matches Listing 7.14.

Figure 7.17  Adding on demand static import

Your code for CrimeFragment is now complete. It would be great if you could run CriminalIntent now and play with the code you have written. But you cannot. Fragments cannot put their views on screen on their own. To realize your efforts, you first have to add a CrimeFragment to CrimeActivity.