如何自定义 CheckBoxPreference 的布局 (maxLines)？

Question

我正在使用以下 settings.xml 来膨胀我的 SettingsFragment 扩展 android.support.v7.preference.PreferenceFragmentCompat:

<android.support.v7.preference.PreferenceScreen 
    xmlns:android="http://schemas.android.com/apk/res/android">

    <android.support.v7.preference.PreferenceCategory 
        android:title="@string/settings_category_title_general">

        <android.support.v7.preference.CheckBoxPreference
            android:defaultValue="@string/settings_default_value_lorem"
            android:key="@string/settings_key_lorem"
            android:summary="@string/settings_summary_lorem"
            android:title="@string/settings_title_lorem" />

    </android.support.v7.preference.PreferenceCategory>

</android.support.v7.preference.PreferenceScreen>

summary文本在四行后被截断com.android.support:preference-v7:24.2.1在res/layout/preferences.xml中定义：

<TextView android:id="@android:id/summary"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@android:id/title"
    android:layout_alignStart="@android:id/title"
    android:textAppearance="?android:attr/textAppearanceSmall"
    android:textColor="?android:attr/textColorSecondary"
    android:maxLines="4" />

布局检查器也显示 summary id：

为了覆盖设置，我定义了以下样式：

<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
    <item name="preferenceTheme">@style/AppPreferenceTheme</item>
</style>

<style name="AppPreferenceTheme" parent="@style/PreferenceThemeOverlay">
    <item name="preferenceStyle">@style/AppPreference</item>
</style>

<style name="AppPreference" parent="@style/Preference">
    <item name="android:layout">@layout/settings_item</item>
</style>

并创建了一个名为 settings_item.xml 的原始布局文件 preferences.xml 的副本，它覆盖了 android:maxLines="4".

但是，样式未应用。我在 summary 视图中添加了 background 颜色来检查这一点。

---

相关

• Building an Android settings screen (Part 4): How to use a custom layout for the Preference fragment

Answer 1

来自JavaDoc of the Preference constructor：

Perform inflation from XML and apply a class-specific base style. This constructor of Preference allows subclasses to use their own base style when they are inflating. For example, a CheckBoxPreference constructor calls this version of the super class constructor and supplies android.R.attr.checkBoxPreferenceStyle for defStyleAttr. This allows the theme's checkbox preference style to modify all of the base preference attributes as well as the CheckBoxPreference class's attributes.

所以将样式更改为：

<style name="AppPreferenceTheme" parent="@style/PreferenceThemeOverlay">
    <item name="checkBoxPreferenceStyle">@style/AppPreference</item>
</style>

<style name="AppPreference" parent="@style/Preference.CheckBoxPreference">
    <item name="layout">@layout/settings_item</item>
</style>