Settings 体系架构二 PreferenceGroup和PreferenceScreen

热度 ℃

Preference只是设置菜单中的某一项，PreferenceGroup则是Preference的容器，负责多个Preference的显示管理，它也是Preference的子类。

PreferenceGroup

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public abstract class PreferenceGroup extends Preference implements GenericInflater.Parent<Preference> {
    /**
     * Preference列表，里面的元素默认情况下根据Preference的order排序。
     * 添加的时候，请使用addPreference，而不要直接使用List#add方法。
     */
    private List<Preference> mPreferenceList;
    private boolean mOrderingAsAdded = true; // 菜单排序顺序是否和添加的顺序保持一致。
    /**
     * 添加Preference到List
     */
    public boolean addPreference(Preference preference) {
        if (mPreferenceList.contains(preference)) {
            return true;
        }
        if (preference.getOrder() == Preference.DEFAULT_ORDER) {
            if (mOrderingAsAdded) {
                preference.setOrder(mCurrentPreferenceOrder++);
            }
        }
        // ...
        synchronized(this) {
            int insertionIndex = Collections.binarySearch(mPreferenceList, preference);
            if (insertionIndex < 0) {
                insertionIndex = insertionIndex * -1 - 1;
            }
            mPreferenceList.add(insertionIndex, preference); // 根据Order添加到指定位置
        }
        preference.onAttachedToHierarchy(getPreferenceManager());
        // 回调Preference的onAttachedToHierarchy，在该方法中，会去设置Preference的一些默认值。
        preference.assignParent(this);
        if (mAttachedToActivity) {
            preference.onAttachedToActivity();
        }
        notifyHierarchyChanged();
        return true;
    }
    public boolean removePreference(Preference preference) {
        final boolean returnValue = removePreferenceInt(preference);
        notifyHierarchyChanged();
        return returnValue;
    }
    private boolean removePreferenceInt(Preference preference) {
        synchronized(this) {
            preference.onPrepareForRemoval();
            if (preference.getParent() == this) {
                preference.assignParent(null);
            }
            return mPreferenceList.remove(preference);
        }
    }
    /**
     * Finds a {@link Preference} based on its key. 
     */
    public Preference findPreference(CharSequence key) {
        if (TextUtils.equals(getKey(), key)) {
            return this;
        }
        final int preferenceCount = getPreferenceCount();
        for (int i = 0; i < preferenceCount; i++) {
            final Preference preference = getPreference(i);
            final String curKey = preference.getKey();
            if (curKey != null && curKey.equals(key)) {
                return preference;
            }
            if (preference instanceof PreferenceGroup) {
                final Preference returnedPreference = ((PreferenceGroup)preference)
                        .findPreference(key);
                if (returnedPreference != null) {
                    return returnedPreference;
                }
            }
        }
        return null;
    }
    @Override
    protected void onAttachedToActivity() {
        super.onAttachedToActivity();
        // Mark as attached so if a preference is later added to this group, we
        // can tell it we are already attached
        mAttachedToActivity = true;
        // Dispatch to all contained preferences
        final int preferenceCount = getPreferenceCount();
        for (int i = 0; i < preferenceCount; i++) {
            getPreference(i).onAttachedToActivity();
        }
    }
}

PreferenceGroup是一个抽象类，它有两个子类PreferenceScreen和PreferenceCategory。

PreferenceCategory

Used to group {@link Preference} objects and provide a disabled title above the group.

PreferenceScreen

Preference元素根容器，在PreferenceActivity或者PreferenceFragment中，用来显示Preference，使用PreferenceManager#createPreferenceScreen(Context)创建实例对象。

该类有两种使用方法：

  • 使用在PreferenceActivity或者PreferenceFragment中，作为root元素，不会显示该类的一些信息，比如Title，只显示里面的Preference。
  • 嵌套使用在Preference中，它作为另一个PreferenceScreen页面(可能是Dialog，也可以是配置Intent跳转到另一个Activity)的入口，并不直接显示里面的Preference子元素。

下面是一个示例：

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<PreferenceScreen
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:settings="http://schemas.android.com/apk/res/com.android.settings"
    android:title="@string/network_dashboard_title">
    <com.android.settings.widget.MasterSwitchPreference
        android:fragment="com.android.settings.wifi.WifiSettings"
        android:key="toggle_wifi"
        android:title="@string/wifi_settings"
        android:summary="@string/summary_placeholder"
        android:icon="@drawable/ic_settings_wireless"
        android:order="-30">
        <intent
            android:action="android.settings.WIFI_SETTINGS"
            android:targetClass="Settings$WifiSettingsActivity"/>
    </com.android.settings.widget.MasterSwitchPreference>
    
    <Preference
        android:fragment="com.android.settings.ProxySelector"
        android:key="proxy_settings"
        android:title="@string/proxy_settings_title"/>
</PreferenceScreen>

PreferenceScreen.java

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public final class PreferenceScreen extends PreferenceGroup implements AdapterView.OnItemClickListener,
        DialogInterface.OnDismissListener {
    private ListAdapter mRootAdapter;
    
    private ListView mListView;
    public void onItemClick(AdapterView parent, View view, int position, long id) {
        // If the list has headers, subtract them from the index.
        if (parent instanceof ListView) {
            position -= ((ListView) parent).getHeaderViewsCount();
        }
        Object item = getRootAdapter().getItem(position);
        if (!(item instanceof Preference)) return;
        final Preference preference = (Preference) item; 
        preference.performClick(this); // 分发点击事件
    }
    
    /**
     * Returns an adapter that can be attached to a {@link PreferenceActivity}
     * or {@link PreferenceFragment} to show the preferences contained in this
     * {@link PreferenceScreen}.
     */
    public ListAdapter getRootAdapter() {
        if (mRootAdapter == null) {
            mRootAdapter = onCreateRootAdapter();
        }   
        return mRootAdapter;
    }
    
    /**
     * Creates the root adapter.
     */
    protected ListAdapter onCreateRootAdapter() {
        return new PreferenceGroupAdapter(this);
    }
    /** 设置视图Adapter
     */
    public void bind(ListView listView) {
        listView.setOnItemClickListener(this);
        listView.setAdapter(getRootAdapter());
        
        onAttachedToActivity();
    }    
}

bind方法在PreferenceFragment中，创建好PreferenceScreen后，会主动调用。

PreferenceGroupAdapter

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public class PreferenceGroupAdapter extends BaseAdapter
        implements OnPreferenceChangeInternalListener {
    private List<Preference> mPreferenceList;
    public View getView(int position, View convertView, ViewGroup parent) {
        final Preference preference = this.getItem(position);
        // Build a PreferenceLayout to compare with known ones that are cacheable.
        mTempPreferenceLayout = createPreferenceLayout(preference, mTempPreferenceLayout);
        // If it's not one of the cached ones, set the convertView to null so that 
        // the layout gets re-created by the Preference.
        if (Collections.binarySearch(mPreferenceLayouts, mTempPreferenceLayout) < 0 ||
                (getItemViewType(position) == getHighlightItemViewType())) {
            convertView = null;
        }
        // 调用Preference#getView获取UI视图
        View result = preference.getView(convertView, parent);
        if (position == mHighlightedPosition && mHighlightedDrawable != null) {
            ViewGroup wrapper = new FrameLayout(parent.getContext());
            wrapper.setLayoutParams(sWrapperLayoutParams);
            wrapper.setBackgroundDrawable(mHighlightedDrawable);
            wrapper.addView(result);
            result = wrapper;
        }
        return result;
    }
}