android4.0中Fragment定製item背景

原創

AnndyPeng

2020-06-28 10:33

我們知道android3.0之後加入了Fragment的使用，這裏探討下我學習Fragment時遇到的定製其item背景的方法。

第一我們要在base/core/res/res/drawable/下定義item背景使用的selector屬性xml文件

1.preference_background_bottom.xml

<selector xmlns:android="http://schemas.android.com/apk/res/android">
  <item android:state_pressed="true" android:drawable="@drawable/preference_background_bottom_pressed" /> 
  <item android:state_focused="true" android:drawable="@drawable/preference_background_bottom_pressed" />
  <item android:drawable="@drawable/preference_background_bottom_normal" />
</selector>

2.preference_background_center.xml

<selector xmlns:android="http://schemas.android.com/apk/res/android">
  <item android:state_pressed="true" android:drawable="@drawable/preference_background_center_pressed" /> 
  <item android:state_focused="true" android:drawable="@drawable/preference_background_center_pressed" />
  <item android:drawable="@drawable/preference_background_center_normal" />
</selector>

3.preference_background_single.xml

<selector xmlns:android="http://schemas.android.com/apk/res/android">
  <item android:state_pressed="true" android:drawable="@drawable/preference_background_single_pressed" /> 
  <item android:state_focused="true" android:drawable="@drawable/preference_background_single_pressed" />
  <item android:drawable="@drawable/preference_background_single_normal" />
</selector>

4.preference_background_top.xml

<selector xmlns:android="http://schemas.android.com/apk/res/android">
  <item android:state_pressed="true" android:drawable="@drawable/preference_background_top_pressed" /> 
  <item android:state_focused="true" android:drawable="@drawable/preference_background_top_pressed" />
  <item android:drawable="@drawable/preference_background_top_normal" />
</selector>

第二我們在base/core/res/res/values/styles.xml中定義一個style

    <style name="Widget.PreferenceListView" parent="Widget.AbsListView">
        <item name="android:listSelector">@android:color/transparent</item>
        <item name="android:divider">@android:drawable/preference_divider</item>
        <item name="android:footerDividersEnabled">false</item>
    </style>

第三我們修改base/core/res/res/layout/preference_list_fragment.xml中ListView使用剛纔定義的style

<ListView android:id="@android:id/list"
        style="@style/Widget.PreferenceListView"
        android:layout_width="match_parent"
        ......

第四修改base/core/java/android/preference/PreferenceGroupAdapter.java類

1.定義兩個變量

private List<Integer> mPreferenceCategoryIndex;    //記錄所有item的index
private int mCurrentIndex;    //記錄當前item的index

2.在構造函數中對mPreferenceCategoryIndex進行初始化

mPreferenceCategoryIndex = new ArrayList<Integer>();

3.在flattenPreferenceGroup函數中更新mPreferenceCategoryIndex的值，修改如下

 private void flattenPreferenceGroup(List<Preference> preferences, PreferenceGroup group) {
        // TODO: shouldn't always?
        group.sortPreferences();

        final int groupSize = group.getPreferenceCount();
        for (int i = 0; i < groupSize; i++, mCurrentIndex++) {
            final Preference preference = group.getPreference(i);
            
            if (preference instanceof PreferenceCategory) {
                mPreferenceCategoryIndex.add(mCurrentIndex + 1);
            }
       ......

4.添加getCurrentCategoryOffset函數，用來獲取當前item位置

private int[] mCCOCache = new int[2];

    private int[] getCurrentCategoryOffset(int position) {
        List<Integer> list = mPreferenceCategoryIndex;
        int end = getCount();
        int size = list.size();
        int offset = 0;

        mCCOCache[0] = 0;
        mCCOCache[1] = end;

        for (int i = size - 1; i >= 0; i--) {
            int t = list.get(i);
            if (position >= t) {
                offset = t;
                mCCOCache[0] = offset;
                if (i < size - 1) {
                    mCCOCache[1] = list.get(i + 1) - 1;
                } else {
                    mCCOCache[1] = end;
                }
                break;
            } else {
                mCCOCache[1] = t - 1;
            }
        }
        return mCCOCache;
    }

5.修改getView方法，處理item的背景，修改原生的return preference.getView(convertView, parent);爲以下：

      ......
        View v = preference.getView(convertView, parent);
        if (!(preference instanceof PreferenceCategory)) {
            int[] offset = getCurrentCategoryOffset(position);
            if (offset[1] - offset[0] == 1) {
                v.setBackgroundResource(com.android.internal.R.drawable.preference_background_single);
            } else if (position == offset[0]) {
                v.setBackgroundResource(com.android.internal.R.drawable.preference_background_top);
            } else if (offset[1] - position == 1) {
                v.setBackgroundResource(com.android.internal.R.drawable.preference_background_bottom);
            } else {
                v.setBackgroundResource(com.android.internal.R.drawable.preference_background_center);
            }
        }
        return v;

到此大功告成，當然你要把selector文件所需要的圖片文件準備好。我用到的背景圖片如下：