我有实现 Closeable 接口的对象，并且希望在我的 ViewModel 清晰时调用 close() 方法。我知道要实现 ViewModel 的 onCleared 方法，但我想在 ViewModel 中使用 mBagOfTags。mBagOfTags 处理可关闭对象（在 clear 方法中调用 close 方法）并且不想在 ViewModel 中创建新的地图对象。如何使用 ViewModel 的 mBagOfTags ？
ViewModel 中的 mBagOfTags 及其成员函数是包私有访问修饰符。
这是android团队开发的ViewModel类。
package androidx.lifecycle;
public abstract class ViewModel {
// Can't use ConcurrentHashMap, because it can lose values on old apis (see b/37042460)
@Nullable
private final Map<String, Object> mBagOfTags = new HashMap<>();
private volatile boolean mCleared = false;
/**
* This method will be called when this ViewModel is no longer used and will be destroyed.
* <p>
* It is useful when ViewModel observes some data and you need to clear this subscription to
* prevent a leak of this ViewModel.
*/
@SuppressWarnings("WeakerAccess")
protected void onCleared() {
}
@MainThread
final void clear() {
mCleared = true;
// Since clear() is final, this method is still called on mock objects
// and in those cases, mBagOfTags is null. It'll always be empty though
// because setTagIfAbsent and getTag are not final so we can skip
// clearing it
if (mBagOfTags != null) {
synchronized (mBagOfTags) {
for (Object value : mBagOfTags.values()) {
// see comment for the similar call in setTagIfAbsent
closeWithRuntimeException(value);
}
}
}
onCleared();
}
/**
* Sets a tag associated with this viewmodel and a key.
* If the given {@code newValue} is {@link Closeable},
* it will be closed once {@link #clear()}.
* <p>
* If a value was already set for the given key, this call does nothing and
* returns currently associated value, the given {@code newValue} would be ignored
* <p>
* If the ViewModel was already cleared then close() would be called on the returned object if
* it implements {@link Closeable}. The same object may receive multiple close calls, so method
* should be idempotent.
*/
@SuppressWarnings("unchecked")
<T> T setTagIfAbsent(String key, T newValue) {
T previous;
synchronized (mBagOfTags) {
previous = (T) mBagOfTags.get(key);
if (previous == null) {
mBagOfTags.put(key, newValue);
}
}
T result = previous == null ? newValue : previous;
if (mCleared) {
// It is possible that we'll call close() multiple times on the same object, but
// Closeable interface requires close method to be idempotent:
// "if the stream is already closed then invoking this method has no effect." (c)
closeWithRuntimeException(result);
}
return result;
}
/**
* Returns the tag associated with this viewmodel and the specified key.
*/
@SuppressWarnings({"TypeParameterUnusedInFormals", "unchecked"})
<T> T getTag(String key) {
if (mBagOfTags == null) {
return null;
}
synchronized (mBagOfTags) {
return (T) mBagOfTags.get(key);
}
}
private static void closeWithRuntimeException(Object obj) {
if (obj instanceof Closeable) {
try {
((Closeable) obj).close();
} catch (IOException e) {
throw new RuntimeException(e);
}
}
}
}
我的 ViewModel 在另一个包中。