在android 11的 InputMethodManager的源码中，查看 windowDismissed()，如下
/**
* An empty method only to avoid crashes of apps that call this method via reflection and do not
* handle {@link NoSuchMethodException} in a graceful manner.
*
* @deprecated This is an empty method. No framework method must call this method.
* @hide
*/
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.
}
/*
* 以下三个字段，在低于 android 10 的版本中是都存在的；之后，有变更。
* 低于 android 10，当Activity dismissed 时，可以通过反射，将它们置null，使它们不再持有该Activity中View的引用，防止内存泄露。
* InputMethodManager#mCurRootView
* InputMethodManager#mServedView
* InputMethodManager#mNextServedView
*
* android 10之后修复了所有已知问题。
* 对于较老的版本，建议使用 androidx.activity.ComponentActivity 及其子类。
* issues/37122102，说明 android N/7.0 (api 24)，就开始了修复。
*
* android 11 source code：http://aospxref.com/android-11.0.0_r21/xref/frameworks/base/core/java/android/view/inputmethod/InputMethodManager.java
* android 10 source code：http://aospxref.com/android-10.0.0_r47/xref/frameworks/base/core/java/android/view/inputmethod/InputMethodManager.java
*/
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()
}
}
