Please explain the guidelines related to the Platform.invokeLater and reuse of cell in tableview

Hello

1.

Whenever I see tableview in JavaFX 2 + I see

  1. @Override   
  2. public Sub updateItem (last element of the string, Boolean void) { }
  3. Super .updateItem (element, empty);   
  4. if (item != null) {   
  5. button.setText (item);
  6. setGraphic (button);
  7. }  else { 
  8. (setGraphic)); /
  9. }
  10. }


    12. So basically, this method is called for each item in my list. Now my questions:

    + where element can be null? I have a list < String > so I don't see the point of what's going on

    + Why does the (null) setGraphic else? Or more if the item is null then null graphics also.


    I understand that this code is related to the loading of data that you highlight and reuse the cells, but it is not clear to me how it works. Please explain a little bit what happens and what makes the super.update done too if possible.


    2.


    1. Platform.runLater (new Runnable() { })
    2. public void run() { 
    3. final Node scrollBar = comboBox.lookup (".scroll-bar: vertical '); 
    4. scrollBar.setOpacity (0,); 
    5. }
    6. });

    In the present code why can't then I just directly called search & 'SetOpacity?

    I suppose that if I call it directly then it will run right in this moment. But if I wrap in this executable, then it is added to a queue of javafx, which will process my application when it can then perhaps do not stress the UI? But I don't know, can you tell if it is correct or not I think?

    I think it's very important for all developers who start with FX to understand the purpose of the present code.

    Thank you

    Desmond

    (When you have two questions, please post two separate interviews. It makes it easier for people to seek and find the answer in the future).

    So basically, this method is called for each item in my list.

    No, actually.

    The cells are just for rendering in your list items. If you have a lot of articles (or even a lot), so some scrolls off the screen, TableCells will not be created for them. In addition, the user scrolls around, the cells that represent the items that scroll off the screen can be used for items that are now visible. The updateItem (...) method will be called to update the cell to display the new item in this case.

    If relatively few cells is created. On the other hand, the updateItem (...) method can be called in quite frequently in certain circumstances as the cells are re-used.

    + where element can be null? I have a list of , so I don't see the point of what's going on

    There are two possibilities:

    1. The cell is empty. Note that in a table with very few objects, the table is filled with empty lines. Those are always represented by cells, which have the empty flag set to true and the item the null value property.
    2. NULL is a valid value perfectly put in (some implementations of) list. Therefore, it is possible that you really have null values in your list. In addition, in a TableView property to the value of the column for a given row can be set to null.

    + Why does the (null) setGraphic else?

    If the cell contained a non-null value before and is updated to represent a null value, then you will need to remove the graphic. (Otherwise you may find yourself with buttons in the empty lines, which is probably not what you want.) This can happen if the lines are removed, or possibly during scrolling like cells are reused (the latter is possible, but it is difficult to see what happens to implementation). In trees, the cells can become empty as nodes in the tree are reduced.

    What makes the super.update makes

    The default TableCell performs a lot of work. He calls the behavior by default until your custom implementation is called. This default behavior includes up-to-date of the item and empty properties to new values, saving listeners of the mouse to the selection behavior and editing behavior if the cell is editable, etc..

    It is not clear to me how it works

    It's not really supposed to be. It is object oriented programming: you're supposed to only rely on the feature (which it does) rather than implementing (how it does). This frees up developers to JavaFX to vary the implementation (to improve performance, for example) from one version to the other, as they did quite significantly from 2.2 JavaFX JavaFX 8. All you know is that some cells are created, they can be reused, and the updateItem (...) method will be called whenever the modification of the element in a particular cell. Which may be because the property that the cell is the changed view, either because the cell was re-used for another element. The cells can become empty due to reuse. No guarantees are made as to how and when reuse will occur. (Make these guarantees would greatly limit the ability of the JavaFX team to change things in the future)

    In the present code why can't then I just directly called search & 'SetOpacity?

    It's not easy without a context, but I guess that this code is in a (...) Platform.runLater to ensure that the nodes were posted on the screen.

    The problem is that research based on css will not succeed usually until a render pass is filed, which is always after the step was established, but can not be immediately after. The Platform.runLater (...) here forces the code to execute after all what is currently pending on the Thread of the FX Application.

    Tags: Java

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