How to reach the elements of the layout using Pref

问题:

I've tried to make a custom preference layout, because I wanted to make a color picker with it.

I used the solution here:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    getFragmentManager().beginTransaction().replace(android.R.id.content, new PrefFragment()).commit();
}

I wanted to edit the value of the TextView on the layout, that's why I added the lines with the TextView in it.

The problem is that it threw a NullPointerException on the setText line, because I think the findViewById() method returned null.

PrefFragment.java:

public class PrefFragment extends PreferenceFragment {

    private TextView titleTV;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        addPreferencesFromResource(R.xml.preferences);
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        titleTV = (TextView) getActivity().findViewById(R.id.title);
        titleTV.setText(R.string.pref_bgcolor);
    }
}

preferences.xml:

<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
<Preference
    android:title="@string/pref_bgcolor"
    android:summary="@string/pref_bgcolor_sum"
    android:key="hu.atsoft.myip.color"
    android:widgetLayout="@layout/color_pref"/>
</PreferenceScreen>

color_pref.xml:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/color_preference">

    <TextView
        android:id="@+id/title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:paddingLeft="5dip"
        android:paddingRight="5dip"
        android:paddingTop="5dip"
        android:singleLine="true"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:textColor="@android:color/black"/>

    <TextView
        android:id="@+id/summary"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:padding="5dip"
        android:layout_alignParentLeft="true"
        android:layout_below="@id/title"
        android:singleLine="true"
        android:textAppearance="?android:attr/textAppearanceSmall"/>

    <ImageView
        android:id="@+id/color_preview"
        android:layout_width="20dip"
        android:layout_height="20dip"
        android:background="@android:color/darker_gray"
        android:layout_alignParentRight="true"
        android:layout_centerVertical="true"
        android:layout_margin="5dip"/>

</RelativeLayout>

What should I use to reach the elements instead of the findViewById() method?

回答1:

You should use custom Preference:

PreferenceWithTip.class

public class PreferenceWithTip extends Preference {
    private static final String TAG = "PreferenceWithTip";
    String pTitle = null;
    String tipstring = null;

    @SuppressLint("Recycle")
    public PreferenceWithTip(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);

        Log.i(TAG,"PreferenceWithTip invoked");
        TypedArray ta = context.obtainStyledAttributes(attrs, R.styleable.PreferenceWithTip);
        tipstring = ta.getString(R.styleable.PreferenceWithTip_tipstring);
        pTitle = ta.getString(R.styleable.PreferenceWithTip_titlestring);
        ta.recycle();
    }

    public PreferenceWithTip(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    @Override
    protected void onBindView(View view) {
        super.onBindView(view);
        TextView pTitleView = (TextView)view.findViewById(R.id.title);
        pTitleView.setText(pTitle);
        TextView pTipView = (TextView)view.findViewById(R.id.summary);
        pTipView.setText(tipstring);
    }

    @Override
    protected View onCreateView(ViewGroup parent) {
        return LayoutInflater.from(getContext()).inflate(R.layout.color_pref,
                parent, false);
    }


}

attr.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="PreferenceWithTip">
        <attr name="tipstring" format="string"></attr>
        <attr name="titlestring" format="string"></attr>
    </declare-styleable>
</resources>

preferences.xml:

<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
<com.test.mytest.PreferenceWithTip
            preference:tipstring="a"
            preference:titlestring="title" >
        </com.test.mytest.PreferenceWithTip>
</PreferenceScreen>