Android Preference 笔记

1.从PreferenceScreen 中删除某个Preference

2. Preference类图

3. Activity&Fragment / Preference&Fragment 组合使用

4. Actionbar （标题：显示与隐藏）

4.1 AppCompatActivity 默认有标题

4.2 PreferenceActivity 默认没有标题

5. Preference 点击回调事件(OnPreferenceClickListener 、OnPreferenceChangeListener)

6. persistent 是否存储在内存中

7. SharedPreferences

1.从PreferenceScreen 中删除某个Preference

（1） . 先获取PreferenceScreen

PreferenceScreen ps = getPreferenceScreen();

（2）. 获取要删除的Preference

Preference pf = findPreference(pfKey); // pfKey 为String类型3. 删除
if (pf != null && ps != null) {ps.removePreference(pf);
}

其中removePreference 会返回 boolean 值，删除成功true, 否正false

从 PreferenceCategory 中删除Preference 也是类似，先要获取PreferenceCategory

2. Preference类图

(1) PreferenceGroup 是Preference 的子类，也是一个抽象类，可以拥有一个或者多个Preference, 类似View 和ViewGroup.

(2) PreferenceScreen 和PreferenceCategory 是PreferenceGroup的子类，扩展少量方法

(3) PreferenceScreen 作为xml 布局文件根标签时，其设置的Titile 是不会显示的(需要设置主题支持Actionbar类型的，才会显示)

PreferenceScreen 内部再嵌套一个PreferenceScreen时（组合），内部的PreferenceScreen会显示Titile（点跳转后!!!），但是其内部的Preference需要点击后才会显示出来

如：

<PreferenceScreenxmlns:android="http://schemas.android.com/apk/res/android"<!--Title 不显示-->android:title="WiFi"android:key="first_preferencescreen"><CheckBoxPreferenceandroid:key="wifi enabled"android:title="WiFi" /><PreferenceScreenandroid:key="second_preferencescreen"<!--Title 显示-->android:title="WiFi settings"><!--内部Preference 不显示！！！！ 需要点击进入后再显示Prefer wifi--><CheckBoxPreferenceandroid:key="prefer wifi"android:title="Prefer WiFi" /></PreferenceScreen>
</PreferenceScreen>

(4) 使用PreferenceCategory 可以显示标题，并且Title这一行不能点击，因为PreferenceCategory内部覆写

public boolean isEnabled() {return false;
}

更多详细可以参考 https://blog.csdn.net/weixin_31767183/article/details/77748421

3. Activity&Fragment / Preference&Fragment 组合使用

其中，PreferenceFragmentCompat 可以自定义定制化的风格，作为父类提供一个app或者一个系统使用，使得风格统一。

(通过依赖库的方式编译进去，一样可以是androidx.preference的包名)

4. Actionbar （标题：显示与隐藏）

标题是否显示与它的主题 (Theme有关)

4.1 AppCompatActivity 默认有标题

    /*** Support library version of {@link android.app.Activity#getActionBar}.** <p>Retrieve a reference to this activity's ActionBar.** @return The Activity's ActionBar, or null if it does not have one.*/@Nullablepublic ActionBar getSupportActionBar() {return getDelegate().getSupportActionBar();}

有两种方式隐藏标题

一种是在AndroidManifest 配置NoActionBar主题, 如 android:theme="@style/Theme.AppCompat.NoActionBar"

        <activityandroid:name=".XXXXActivity"android:theme="@style/Theme.AppCompat.NoActionBar"><intent-filter><action android:name="android.intent.action.MAIN" /></intent-filter></activity>

另一种是在代码里配置，如

getSupportActionBar().hide()

4.2 PreferenceActivity 默认没有标题

如果要显示标题，在代码里配置主题 (可以引用android 库里的主题)

    @Overrideprotected void onCreate(@Nullable Bundle savedInstanceState) {if(Build.VERSION.SDK_INT> Build.VERSION_CODES.HONEYCOMB_MR2){this.setTheme(android.R.style.Theme_DeviceDefault);}
}

5. Preference 点击回调事件(onClick /OnPreferenceClickListener 、OnPreferenceChangeListener)

在 onBindViewHolder 的时候，设置 onClickListener, 这个listener 其实就是实现 View 的OnClickListener, Preference 内部交给performClick 处理。详见后面

    private final View.OnClickListener mClickListener = new View.OnClickListener() {@Overridepublic void onClick(View v) {performClick(v);}};public void onBindViewHolder(PreferenceViewHolder holder) {View itemView = holder.itemView;Integer summaryTextColor = null;itemView.setOnClickListener(mClickListener);

提供点击监听的回调接口给客户端，客户端可以决定是否响应事件 以及 在更新Preference 前进行设置操作(如设置Summary)

通过返回true 或者 false 告诉系统。 (例如客户端在CheckBoxPreference中设置了监听，实现了OnPreferenceChangeListener，但是返回值为false, 则不会进行更新操作checked)

    /*** Interface definition for a callback to be invoked when a {@link Preference} is* clicked.** @deprecated Use the <a href="{@docRoot}jetpack/androidx.html">AndroidX</a>*      <a href="{@docRoot}reference/androidx/preference/package-summary.html">*      Preference Library</a> for consistent behavior across all devices.*      For more information on using the AndroidX Preference Library see*      <a href="{@docRoot}guide/topics/ui/settings.html">Settings</a>.*/@Deprecatedpublic interface OnPreferenceClickListener {/*** Called when a Preference has been clicked.** @param preference The Preference that was clicked.* @return True if the click was handled.*/boolean onPreferenceClick(Preference preference);}

    /*** Interface definition for a callback to be invoked when the value of this* {@link Preference} has been changed by the user and is* about to be set and/or persisted.  This gives the client a chance* to prevent setting and/or persisting the value.** @deprecated Use the <a href="{@docRoot}jetpack/androidx.html">AndroidX</a>*      <a href="{@docRoot}reference/androidx/preference/package-summary.html">*      Preference Library</a> for consistent behavior across all devices.*      For more information on using the AndroidX Preference Library see*      <a href="{@docRoot}guide/topics/ui/settings.html">Settings</a>.*/@Deprecatedpublic interface OnPreferenceChangeListener {/*** Called when a Preference has been changed by the user. This is* called before the state of the Preference is about to be updated and* before the state is persisted.** @param preference The changed Preference.* @param newValue The new value of the Preference.* @return True to update the state of the Preference with the new value.*/boolean onPreferenceChange(Preference preference, Object newValue);}

performClick 里的逻辑，如果有为Preference 设置intent ，则会调用startActivity 跳转

    @RestrictTo(LIBRARY_GROUP_PREFIX)public void performClick() {if (!isEnabled() || !isSelectable()) {return;}onClick();if (mOnClickListener != null && mOnClickListener.onPreferenceClick(this)) {return;}PreferenceManager preferenceManager = getPreferenceManager();if (preferenceManager != null) {PreferenceManager.OnPreferenceTreeClickListener listener = preferenceManager.getOnPreferenceTreeClickListener();if (listener != null && listener.onPreferenceTreeClick(this)) {return;}}if (mIntent != null) {Context context = getContext();context.startActivity(mIntent);}}

6. persistent 是否存储在内存中(android:persistent="true")

        <!-- Whether the Preference stores its value to the storage. --><attr name="persistent" />

    <!-- Flag to control special persistent mode of an application.  This shouldnot normally be used by applications; it requires that the system keepyour application running at all times. --><attr name="persistent" format="boolean" />

如果是false，则退出Preference 后，再进入，值不会保存。

6.1 CheckBoxPreference（TwoStatePreference）

在响应onClick 的时候，会回调（如果有注册监听），并在setChecked的时候，调用persistXXX(例如 persistBoolean）进行存储。

因此使用Preference 后，会对其xml 定义的key值进行存储，不需要手动调用SharePreference.edit.putXXX(key, value).apply 进行存储。

默认值可以用 android.defaultValue 设置，会存储到Preference 对应的SharePreference中

//TwoStatePreference.java@Overrideprotected void onClick() {super.onClick();final boolean newValue = !isChecked();if (callChangeListener(newValue)) {setChecked(newValue);}}/*** Sets the checked state and saves it to the {@link SharedPreferences}.** @param checked The checked state.*/public void setChecked(boolean checked) {// Always persist/notify the first time; don't assume the field's default of false.final boolean changed = mChecked != checked;if (changed || !mCheckedSet) {mChecked = checked;mCheckedSet = true;persistBoolean(checked);if (changed) {notifyDependencyChange(shouldDisableDependents());notifyChanged();}}}

//Preference.java/*** Attempts to persist a boolean if this Preference is persistent.** @param value The value to persist.* @return True if this Preference is persistent. (This is not whether the*         value was persisted, since we may not necessarily commit if there*         will be a batch commit later.)* @see #persistString(String)* @see #getPersistedBoolean(boolean)*/protected boolean persistBoolean(boolean value) {if (!shouldPersist()) {return false;}if (value == getPersistedBoolean(!value)) {// It's already there, so the same as persistingreturn true;}PreferenceDataStore dataStore = getPreferenceDataStore();if (dataStore != null) {dataStore.putBoolean(mKey, value);} else {SharedPreferences.Editor editor = mPreferenceManager.getEditor();editor.putBoolean(mKey, value);tryCommit(editor);}return true;}

6.2 普通Preference 存储字符串

/*** Attempts to persist a String if this Preference is persistent.** @param value The value to persist.* @return True if this Preference is persistent. (This is not whether the*         value was persisted, since we may not necessarily commit if there*         will be a batch commit later.)* @see #getPersistedString(String)*/protected boolean persistString(String value) {if (!shouldPersist()) {return false;}// Shouldn't store nullif (TextUtils.equals(value, getPersistedString(null))) {// It's already there, so the same as persistingreturn true;}PreferenceDataStore dataStore = getPreferenceDataStore();if (dataStore != null) {dataStore.putString(mKey, value);} else {SharedPreferences.Editor editor = mPreferenceManager.getEditor();editor.putString(mKey, value);tryCommit(editor);}return true;}

读取存储的字符串

    /*** Attempts to get a persisted String if this Preference is persistent.** @param defaultReturnValue The default value to return if either this*            Preference is not persistent or this Preference is not present.* @return The value from the data store or the default return*         value.* @see #persistString(String)*/protected String getPersistedString(String defaultReturnValue) {if (!shouldPersist()) {return defaultReturnValue;}PreferenceDataStore dataStore = getPreferenceDataStore();if (dataStore != null) {return dataStore.getString(mKey, defaultReturnValue);}return mPreferenceManager.getSharedPreferences().getString(mKey, defaultReturnValue);}

7. SharedPreferences

是一个接口???

根据同一个Context 获取到的SharePreference，对命名相同key赋值或者读取时，实际是对同一个Key操作

public class ContextWrapper extends Context {@UnsupportedAppUsageContext mBase;//....@Overridepublic SharedPreferences getSharedPreferences(String name, int mode) {return mBase.getSharedPreferences(name, mode);}
}

8. 自定义Preference (如添加一个Preference 的属性值)

8.1 attrs.xml 添加自定义类型(declare-styleable)

其中，entryValue 为属性值， groupKey 则可以拓展为当前Preference 属于哪一个Group 组

<?xml version="1.0" encoding="utf-8"?>
<resources><declare-styleable name="XXXPreference"><attr name="entryValue" format="string"></attr><attr name="groupKey" format="string"></attr></declare-styleable>
</resources>

8.2 获取自定义的属性值

通过TypedArray

    public XXXPreference(Context context, AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.XXXPreference, 0, 0);String key = getKey();if (key != null) {mKey = key;}mGroupKey = a.getText(R.styleable.RadioPreference_groupKey).toString();mValue = a.getText(R.styleable.RadioPreference_entryValue).toString();a.recycle();}

注意：XML 定义的Preference 的默认构造函数是

    public XXXGroupPreference(Context context, AttributeSet attrs) {this(context, attrs, 0);setWidgetLayoutResource(R.layout.radiogroup);mContext = context;}

其中 radiogroup 为自定义的布局

8.3 XML 文件使用自定义Preference

其中app:entryValue 和 app:groupKey 即为自定义的属性（xml文件的根标签需要添加工具 xmlns:app="http://schemas.android.com/apk/res-auto"）

                <com.example.Test.XXXPreferenceandroid:key="@string/pref_test"android:defaultValue="false"android:persistent="true"app:entryValue="@string/val_test_value"app:groupKey="@string/pref_test_group"android:title="@string/title_test" />

这样，可以为Preference 新增一个属性，并且可以在XML 使用时赋值，简单明了。

(也可以在定义一个数组，在代码中为各个Preference的自定义属性赋值)