fragment 异常 InstantiationException

接手的项目过了下firebase和内存泄漏，还是有很多常见共性的问题

 这个异常也是非常常见，但是很多人不会去修复的

Caused by: androidx.fragment.app.Fragment$InstantiationException: Unable to instantiate fragment com.healthfitness.me.ui.badgeinfo.BadgeListInfoDialog: could not find Fragment constructorat androidx.fragment.app.Fragment.instantiate(Fragment.java:687)at androidx.fragment.app.FragmentContainer.instantiate(FragmentContainer.java:57)at androidx.fragment.app.FragmentManager$3.instantiate(FragmentManager.java:525)at androidx.fragment.app.FragmentState.instantiate(FragmentState.java:84)at androidx.fragment.app.FragmentStateManager.<init>(FragmentStateManager.java:91)at androidx.fragment.app.FragmentManager.restoreSaveStateInternal(FragmentManager.java:2562)at androidx.fragment.app.Fragment.restoreChildFragmentState(Fragment.java:1988)at androidx.fragment.app.Fragment.onCreate(Fragment.java:1967)at androidx.fragment.app.Fragment.performCreate(Fragment.java:3094)at androidx.fragment.app.FragmentStateManager.create(FragmentStateManager.java:504)at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:268)

原因是

• Android 系统在重建 Fragment 时，只能通过无参构造函数反射生成实例。

• 如果自定义了带参数的构造函数，系统无法找到无参构造方法，直接崩溃。

• 通过 Bundle 传递参数是 Android 的官方推荐做法。

比如很常见的

class BadgeListInfoDialog(private val uId: Long,private val bId: Long,private val isMe: Boolean = true,//表示查看自己的private val badgeUserInfo: BadgeUserInfo? = null,//个人信息private val equipBId: Long?=null,private val mBadgeDetailBean: BadgeDetailBean?=null,//勋章详情，如果外层已经获取到了，就不用再请求了private val isDisBadgeBid: Long?=null
) : BaseDialogFragment<DialogBadgeListInfoBinding>()

BadgeListInfoDialog有了有参数的构造函数，就没有了默认的无参构造函数

所以比如页面销毁重建的时候，就会报这个异常

改造方案

class BadgeListInfoDialog : BaseDialogFragment<DialogBadgeListInfoBinding>() {// 定义参数 Key（避免硬编码）companion object {private const val KEY_UID = "uId"private const val KEY_BID = "bId"private const val KEY_IS_ME = "isMe"private const val KEY_BADGE_USER_INFO = "badgeUserInfo"private const val KEY_EQUIP_BID = "equipBId"private const val KEY_BADGE_DETAIL_BEAN = "badgeDetailBean"private const val KEY_IS_DIS_BADGE_BID = "isDisBadgeBid"// 统一的创建方法fun newInstance(uId: Long,bId: Long,isMe: Boolean = true,badgeUserInfo: BadgeUserInfo? = null,equipBId: Long? = null,badgeDetailBean: BadgeDetailBean? = null,isDisBadgeBid: Long? = null): BadgeListInfoDialog {val args = Bundle().apply {putLong(KEY_UID, uId)putLong(KEY_BID, bId)putBoolean(KEY_IS_ME, isMe)putParcelable(KEY_BADGE_USER_INFO, badgeUserInfo)equipBId?.let { putLong(KEY_EQUIP_BID, it) }putSerializable(KEY_BADGE_DETAIL_BEAN, badgeDetailBean)isDisBadgeBid?.let { putLong(KEY_IS_DIS_BADGE_BID, it) }}return BadgeListInfoDialog().apply {arguments = args}}}// 其他代码...
}

在oncreate中

class BadgeListInfoDialog : BaseDialogFragment<DialogBadgeListInfoBinding>() {// 定义参数变量（添加 lateinit 或可空类型）private lateinit var uId: Longprivate lateinit var bId: Longprivate var isMe: Boolean = trueprivate var badgeUserInfo: BadgeUserInfo? = nullprivate var equipBId: Long? = nullprivate var mBadgeDetailBean: BadgeDetailBean? = nullprivate var isDisBadgeBid: Long? = nulloverride fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)// 从 Bundle 中解析参数arguments?.let { args ->uId = args.getLong(KEY_UID)bId = args.getLong(KEY_BID)isMe = args.getBoolean(KEY_IS_ME, true)badgeUserInfo = args.getParcelable(KEY_BADGE_USER_INFO)equipBId = if (args.containsKey(KEY_EQUIP_BID)) args.getLong(KEY_EQUIP_BID) else nullmBadgeDetailBean = args.getSerializable(KEY_BADGE_DETAIL_BEAN) as? BadgeDetailBeanisDisBadgeBid = if (args.containsKey(KEY_IS_DIS_BADGE_BID)) args.getLong(KEY_IS_DIS_BADGE_BID) else null}}// 其他代码...
}