Android Preference的使用以及解析

简单使用

1. values.arrays.xml

<?xml version="1.0" encoding="utf-8"?>
<resources><string-array name="list_entries"><item>Option 1</item><item>Option 2</item><item>Option 3</item></string-array><string-array name="list_values"><item>1</item><item>2</item><item>3</item></string-array>
</resources>

2. xml.preferences.xml

<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android"><Preferenceandroid:key="simple_preference"android:summary="This is a simple preference"android:title="Simple Preference" /><CheckBoxPreferenceandroid:defaultValue="false"android:key="checkbox_preference"android:summary="This is a CheckBox"android:title="Check Box Preference" /><EditTextPreferenceandroid:dialogTitle="Enter Text"android:key="edittext_preference"android:summary="Enter your text here"android:title="Edit Text Preference" /><ListPreferenceandroid:defaultValue="1"android:entries="@array/list_entries"android:entryValues="@array/list_values"android:key="list_preference"android:summary="Select an option"android:title="List Preference" /><com.example.kotlinlearn.Preference.CustomSeekBarPreferenceandroid:defaultValue="50"android:key="seekbar_preference"android:title="SeekBar Preference" />
</PreferenceScreen>

3. SettingsFragment

package com.example.kotlinlearn.Preference
import android.os.Bundle
import android.util.Log
import androidx.preference.CheckBoxPreference
import androidx.preference.EditTextPreference
import androidx.preference.Preference
import androidx.preference.PreferenceFragmentCompat
import com.example.kotlinlearn.R
class SettingsFragment : Preference.OnPreferenceClickListener,Preference.OnPreferenceChangeListener, PreferenceFragmentCompat() {var TAG = "SettingsFragment"override fun onCreatePreferences(savedInstanceState: Bundle?, rootKey: String?) {setPreferencesFromResource(R.xml.preferences, rootKey)var findPreference = findPreference<EditTextPreference>("edittext_preference")findPreference?.onPreferenceClickListener = thisfindPreference?.onPreferenceChangeListener = this}override fun onPreferenceClick(preference: Preference?): Boolean {Log.d(TAG, "onPreferenceClick: ")return false}override fun onPreferenceChange(preference: Preference?, newValue: Any?): Boolean {Log.d(TAG, "onPreferenceChange: ")return false}
}

4. PreferenceActivity

package com.example.kotlinlearn.Preferenceimport android.os.Bundle
import androidx.activity.enableEdgeToEdge
import androidx.appcompat.app.AppCompatActivity
import androidx.core.view.ViewCompat
import androidx.core.view.WindowInsetsCompat
import com.example.kotlinlearn.Rclass PreferenceActivity : AppCompatActivity() {override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)setContentView(R.layout.activity_preference)// Display the fragment as the main content.supportFragmentManager.beginTransaction().replace(R.id.fragment_container, SettingsFragment()).commit()}
}

效果

原理

1. 布局：RecyclerView进行布局，PreferenceGroupAdapter，重写onCreateViewHolder()、onBindViewHolder()、getItemCount()
   在onCreateViewHolder(ViewGroup parent, int viewType) 中根据viewType判断获取不同的preference。
2. Preference：底层调用SharedPreferences进行保存。通过以下方法持久化数值。
   persistString，persistStringSet，persistInt，persistFloat，persistLong，persistBoolean
   

自定义Preference

重点在监听view变化，在变化后通过回调，将终值写入SharedPreferences，在初始化的时候读出值并赋给view。

package com.example.kotlinlearn.Preferenceimport android.content.Context
import android.content.res.TypedArray
import android.util.AttributeSet
import androidx.preference.Preference
import androidx.preference.PreferenceViewHolder
import android.widget.SeekBar
import android.widget.TextView
import androidx.recyclerview.widget.RecyclerView
import com.example.kotlinlearn.Rclass CustomSeekBarPreference(context: Context, attrs: AttributeSet) : Preference(context, attrs) {private var currentValue: Int = 0private var maxValue: Int = 100init {widgetLayoutResource = R.layout.preference_seekbar}override fun onBindViewHolder(holder: PreferenceViewHolder) {super.onBindViewHolder(holder)val seekBar = holder.findViewById(R.id.seekbar) as SeekBarval valueText = holder.findViewById(R.id.seekbar_value) as TextViewseekBar.max = maxValueseekBar.progress = currentValuevalueText.text = currentValue.toString()seekBar.setOnSeekBarChangeListener(object : SeekBar.OnSeekBarChangeListener {override fun onProgressChanged(seekBar: SeekBar?, progress: Int, fromUser: Boolean) {currentValue = progressvalueText.text = progress.toString()persistInt(progress)}override fun onStartTrackingTouch(seekBar: SeekBar?) {}override fun onStopTrackingTouch(seekBar: SeekBar?) {}})}override fun onGetDefaultValue(a: TypedArray, index: Int): Any {return a.getInt(index, 0)}override fun onSetInitialValue(defaultValue: Any?) {currentValue = getPersistedInt(defaultValue as? Int ?: 0)}
}

ex：

1.当xml中设置组件的id相同时，会导致多个preference的值相同。