Android 解决InputMethodManager 内存泄露问题

在android 11的 InputMethodManager的源码中，查看 windowDismissed()，如下

public void windowDismissed(IBinder appWindowToken) {
    // Intentionally empty.
    //
    // It seems that some applications call this method via reflection to null clear the
    // following fields that used to exist in InputMethodManager:
    //  * InputMethodManager#mCurRootView
    //  * InputMethodManager#mServedView
    //  * InputMethodManager#mNextServedView
    // so that these objects can be garbage-collected when an Activity gets dismissed.
    //
    // It is indeed true that older versions of InputMethodManager had issues that prevented
    // these fields from being null-cleared when it should have been, but the understanding of
    // the engineering team is that all known issues have already been fixed as of Android 10.
    //
    // For older devices, developers can work around the object leaks by using
    // androidx.activity.ComponentActivity.
    // See https://issuetracker.google.com/u/1/issues/37122102 for details.
    //
    // If you believe InputMethodManager is leaking objects in API 24 or any later version,
    // please file a bug at https://issuetracker.google.com/issues/new?component=192705.
}

解决方案：对于低于android10，且非 ComponentActivity的context，反射获取InputMethodManager对象中的 mCurRootView、mServedView、mNextServedView这三个属性，转换为View类型后，判断view的context等于要释放的Activity的context时，将这个属性置为null。

fun fixMemoryLeak(context: Context?) {
    try {
        context ?: return
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) return // android 10 已修复
        if (context is ComponentActivity) return // androidx.activity.ComponentActivity 已修复
        val imm = context.getSystemService(Context.INPUT_METHOD_SERVICE) as? InputMethodManager ?: return
        imm.javaClass.declaredFields.filter {
            it.name == "mCurRootView" || it.name == "mServedView" || it.name == "mNextServedView"
        }.forEach { filed ->
            val origin = filed.isAccessible
            if (!origin) {
                filed.isAccessible = true
            }
            (filed.get(imm) as? View)?.takeIf { it.context == context }?.also {
                filed.set(imm, null)
            }
            filed.isAccessible = origin
        }
    } catch (e: Exception) {
        e.printStackTrace()
    }
}