CODEWITHSUNDEEP
apache-flexdata-binding
wangf
wangf

Reputation: 925

Flex data binding re-bind when data model not change, possible?

There is a common case that I bind a data model value to a GUI control, say, a TextInput. The data model is retrieve from backend.

If user change the value of the TextInput, then click refresh button to retrieve the data model from backend again, the GUI value will not change back. Re-binding not happen, Since the value of data model not changed, no propertyChanged event fired.

In this case, I must Programmatically set the model value to the GUI after data refreshing done.

I know bi-directional binding can solve this problem(when user change value on GUI, set the new value to data model immediately). But sometimes I cannot use bi-directional binding, for example, the data model is a int, but user input a non-int value, I cannot set the value to data model. So the value in data model do not change, when refresh data, rebinding still not happen.

This will make the data binding useless. How to resolve this?

I put pseudo-code here for now, I will put real code later:

1. retrieve a data model from server, via blazeds or something else.
2. bind the model to a TextInput on GUI.
3. user change the TextInput text.
4. User click a refresh button, triger retrieve the model value again.
5. Now since the model value do not change, no PropertyChanged event fired.
6. GUI value still is the user's input, not the value from the model.

I can clear the model value before set the velue back, make re-binding happen.(but sometimes you do not know how to clean the model value, take int for example, you may do not know the original value and happen set the same value). Or I can manually set the model value to GUI. But both are not good looking. bi-directional binding not work since if user input a invalid value, I cannot set it to the model. Model value do not change, re-bind will not happen.

Upvotes: 0

Views: 1152

Answers (3)

Amy Blankenship
Amy Blankenship

Reputation: 6961

You can dispatch binding events whenever you want. One way is to simply dispatch a PropertyChangeEvent on all properties you want to update, but another is to add your own binding event in addition to standard binding.

For instance, I think this will work:

[Bindable]
[Bindable (event="allChanged")]//make sure to dispatch this yourself when everything changes
public var myInt:int;

There is a possibility that the custom binding event might prevent Flex from generating the code in the background that does standard binding (I have never done the above, because if I am going to use custom events, I tend to not use the standard binding).

Flash Builder 4.5 has awesome code generation, so you can just convert a public variable to a getter and setter, and it will ask you if you want to fire a custom event for the property. If you check that box, it will write the code for you. Then you add the second metadata tag by hand.

The getter/setter method will perform better, because then each property will have its own event, rather than all of them firing on propertyChange and checking if the property is the correct one. But the other one is less verbose and more maintainable, if it works.

Upvotes: 1

Vladimir Tsvetkov
Vladimir Tsvetkov

Reputation: 3013

Bidirectional binding can be achieved in a variety of ways, not necessarily with the @-symbol. In your particular case you need to use the Binding-tag:

<fx:Binding source="parseInt(someNumberInput.text)"
    destination="someModel.someNumberValue"/>

<s:TextInput id="someNumberInput" text="{someModel.someNumberValue}"/>

It's very important not to forget to parseInt() the numeric value.

Upvotes: 3

LoremIpsum
LoremIpsum

Reputation: 4428

Use a relevant editor to edit a numeric value. Flex can not guess what you want to do.

Upvotes: 0

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