Android的设置界面实现比较简单,有时甚至只需要使用一个简单的xml文件即可.声明简单,但是如何从PreferenceScreen或者PreferenceCategory中删除一个Preference会简单么.为什么有些人写的就无法删除成功呢?本文将从Android源码实现来分析一下.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 | <?xml version="1.0" encoding="utf-8"?> <PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android" android:key="root"> <PreferenceCategory android:key="theme" android:title="Theme" android:summary="Theme Settings" > <CheckBoxPreference android:key="holo_theme" android:title="Holo Theme" android:summary="Use Holo Theme" /> </PreferenceCategory> <CheckBoxPreference android:key="rmcache" android:title="Auto Clear Cache" android:summary="Enable Auto Clear Cache " /> </PreferenceScreen> |
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1 2 3 | PreferenceScreen screen = getPreferenceScreen(); CheckBoxPreference autoClearCheckboxPref = (CheckBoxPreference) screen.findPreference("rmcache"); screen.removePreference(autoClearCheckboxPref); |
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1 2 3 | PreferenceCategory themePrefCategory = (PreferenceCategory) screen.findPreference("theme"); CheckBoxPreference holoCheckboxPref = (CheckBoxPreference)themePrefCategory.findPreference("holo_theme"); themePrefCategory.removePreference(holoCheckboxPref); |
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很多人出现了删除失败的问题,主要原因是使用了非父亲节点来删除,比如这样
1 2 3 | PreferenceScreen screen = getPreferenceScreen(); CheckBoxPreference holoCheckboxPref = (CheckBoxPreference)screen.findPreference("holo_theme"); screen.removePreference(holoCheckboxPref); |
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PreferenceGroup删除实现,其实PreferenceScreen和PreferenceCategory都是PreferenceGroup的子类.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 | /** * Removes a {@link Preference} from this group. * * @param preference The preference to remove. * @return Whether the preference was found and removed. */ public boolean removePreference(Preference preference) { final boolean returnValue = removePreferenceInt(preference); notifyHierarchyChanged(); return returnValue; } private boolean removePreferenceInt(Preference preference) { synchronized(this) { preference.onPrepareForRemoval(); return mPreferenceList.remove(preference); } } |
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而mPreferenceList中存放的都是当前PreferenceGroup的直接子Preference.
findPreference查找不仅仅限于直接子Preference,会遍历其所有的子Preference.
所以代码中同样有root PreferenceGroup和直接父PreferenceGroup引用时,通常后者效率会高.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 | /** * Finds a {@link Preference} based on its key. If two {@link Preference} * share the same key (not recommended), the first to appear will be * returned (to retrieve the other preference with the same key, call this * method on the first preference). If this preference has the key, it will * not be returned. * <p> * This will recursively search for the preference into children that are * also {@link PreferenceGroup PreferenceGroups}. * * @param key The key of the preference to retrieve. * @return The {@link Preference} with the key, or null. */ 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; } |
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为什么findPreference遍历所有的子节点,而removePreference不会,只会删除直接子Preference