Settings 体系架构三 PreferenceFragment

热度 ℃

PreferenceFragment，在整个Settings应用中，基本所有的页面都继承自它，比如DashboardFragment，它是大多数页面的父类。

PreferenceFragment将Preference显示成列表，Preference将自动保存到SharedPreferences中(如果Preference的persist设置为true的情况下)。调用PreferenceManager#getDefaultSharedPreferences()会自动生成对应的存储设置值的SharedPreferences，在该类中将使用这个SharedPreferences。

PreferenceScreen应当作为root根元素容器，它里面包含了子Preference，PreferenceScreen有两种创建方式：

  • addPreferencesFromResource: 从xml资源文件中构建PreferenceScreen；
  • addPreferencesFromIntent: 通过在manifest中给Activity配置PreferenceManager#METADATA_KEY_PREFERENCES指向一个xml资源；
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/**
 * Adds preferences from activities that match the given {@link Intent}.
 */
public void addPreferencesFromIntent(Intent intent) {
    requirePreferenceManager();
    setPreferenceScreen(mPreferenceManager.inflateFromIntent(intent, getPreferenceScreen()));
}
/**
 * Inflates the given XML resource and adds the preference hierarchy 
 * to the current preference hierarchy.
 */
public void addPreferencesFromResource(@XmlRes int preferencesResId) {
    requirePreferenceManager();
    setPreferenceScreen(mPreferenceManager.inflateFromResource(getActivity(),
            preferencesResId, getPreferenceScreen()));
}
/**
 * Sets the root of the preference hierarchy that this fragment is showing.
 */
public void setPreferenceScreen(PreferenceScreen preferenceScreen) {
    if (mPreferenceManager.setPreferences(preferenceScreen) && preferenceScreen != null) {
        onUnbindPreferences();
        mHavePrefs = true;
        if (mInitDone) { 
            postBindPreferences(); /** 发送更新UI的消息 */
        }
    }
}

onCreateView

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private int mLayoutResId = com.android.internal.R.layout.preference_list_fragment;
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container,
        @Nullable Bundle savedInstanceState) {
    TypedArray a = getActivity().obtainStyledAttributes(null,
            com.android.internal.R.styleable.PreferenceFragment,
            com.android.internal.R.attr.preferenceFragmentStyle,
            0);
    mLayoutResId = a.getResourceId(com.android.internal.R.styleable.PreferenceFragment_layout,
            mLayoutResId);
    a.recycle();
    return inflater.inflate(mLayoutResId, container, false);
}

onCreateView方法根据layoutId，加载View布局UI视图，该视图里面有一个ListView。

更新UI

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private static final int MSG_BIND_PREFERENCES = 1;
private Handler mHandler = new Handler() {
    @Override
    public void handleMessage(Message msg) {
        switch (msg.what) {
            case MSG_BIND_PREFERENCES:
                bindPreferences();
                break;
        }
    }
};
/** 发送更新UI的消息 */
private void postBindPreferences() {
    if (mHandler.hasMessages(MSG_BIND_PREFERENCES)) return;
    mHandler.obtainMessage(MSG_BIND_PREFERENCES).sendToTarget();
}
/** 绑定界面，设置Adapter */
private void bindPreferences() {
    final PreferenceScreen preferenceScreen = getPreferenceScreen();
    if (preferenceScreen != null) {
        View root = getView();
        if (root != null) {
            View titleView = root.findViewById(android.R.id.title);
            if (titleView instanceof TextView) {
                CharSequence title = preferenceScreen.getTitle();
                if (TextUtils.isEmpty(title)) {
                    titleView.setVisibility(View.GONE);
                } else {
                    ((TextView) titleView).setText(title);
                    titleView.setVisibility(View.VISIBLE);
                }
            }
        }
        preferenceScreen.bind(getListView());
        // bind视图，里面调用ListView.setAdapter...
    }
    onBindPreferences();
}

类关系

Struct

PreferenceScreen创建流程

PreferenceScreen_init

PreferenceScreen创建成功后，通过setPreferenceScreen最终会更新UI界面。