android - 如何在 Flutter 中将事件从一个有状态的小部件广播到另一个
问题描述
我想将一个有状态小部件的事件广播到另一个,但似乎找不到办法。我安装了这个插件:事件:^1.1.4 但它没有触发。我想要下面的东西:
Stateful Widget 1:
SomeEventClass.broadcastEvent();
Stateful Widget 2:
SomeEventClass.subscribe();
解决方案
通过使用这样的东西。
class ContinuousStream {
_DataStore _mStorage = _DataStore.getInstance();
/// Sets a new value [value] to the data stream [stream].
/// If there are active subscribers, the value will be dispatched to them.
void emit(String stream, var value) {
_mStorage?.setValue(stream, value);
}
/// Subscribes to the given stream [stream].
/// If stream already has data set, it will be delivered to the [callback] function.
void on(String stream, void Function(Object) callback) {
_mStorage?.setCallback(stream, callback);
}
/// Returns the current value of a given data [stream].
Object getValue(String stream) {
return _mStorage?.getValue(stream);
}
}
// Storage class for ContinuousStream.
class _DataStore {
// Singleton Instance for DataStore
static _DataStore _instance;
// Map instance to store data values with data stream.
HashMap<String, _DataItem> _mDataItemsMap = HashMap();
// Sets/Adds the new value to the given key.
void setValue(String key, var value) {
// Retrieve existing data item from map.
_DataItem item = _mDataItemsMap[key];
item ??= _DataItem();
// Set new value to new/existing item.
item.value = value;
// Reset item to the map.
_mDataItemsMap[key] = item;
// Dispatch new value to all callbacks.
item.callbacks?.forEach((callback) {
callback(value);
});
}
// Sets/Adds the new callback to the given data stream.
void setCallback(String key, Function(Object) callback) {
if (callback != null) {
// Retrieve existing data item from the map.
_DataItem item = _mDataItemsMap[key];
item ??= _DataItem();
// Retrieve callback functions from data item.
List<Function(Object)> callbacks = item.callbacks;
// Check if callback functions exists or not.
if (callbacks == null) {
// If it's null then create new List.
callbacks = List();
// Set callback functions list to data item.
item.callbacks = callbacks;
// Set the data item to the map.
_mDataItemsMap[key] = item;
}
// Add the given callback into List of callback functions.
callbacks.add(callback);
// Dispatch value to the callback function if value already exists.
if (item.value != null) {
callback(item.value);
}
}
}
// Returns current value of the data stream.
Object getValue(String key) {
return _mDataItemsMap[key].value;
}
// Returns singleton instance of _DataStore
static _DataStore getInstance() {
_instance ??= _DataStore();
return _instance;
}
}
// Data class to hold value and callback functions of a data stream.
class _DataItem {
var value;
List<Function(Object)> callbacks;
}
一旦创建了此类,您就可以初始化和访问流。例如,这需要在 StateFulWidget 1 和 StateFUlWidget 2 中完成。
ContinuousStream continuousStream = new ContinuousStream();
然后从 StateFulWidget1:
void send() {
String message = "Hello";
continuousStream.emit("chat-message", message);
}
这对应于您的广播事件。
从 StatefulWidget2 开始:
continuousStream.on("chat-message", (message) {
print("Message Received: $message");
});
这对应于您的订阅事件。这应该可以解决您的问题。
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