Changing label.visibility with a method - Why won't it hide?

问题

I want to be able to set any label's visibility to true or false with a method. I have this code:

private void Change_Visible(Label toBeChanged)
{
    if (toBeChanged.Visible == false)
    {
        toBeChanged.Visible = true;
    }
    else
    {
        toBeChanged.Visible = false;
    }
    toBeChanged.Refresh();
}

I call to this code with:

    Change_Visible(myLabel);
    //
    // Do other things
    //
    Change_Visible(myLabel);

In my specific example, myLabel is set to not be visible at the load of my form. After the first call to Change_Visible it becomes visible, but after the second call to Change_Visible nothing happens. Can you help me make it disappear?

I have already tried some other logics looking for a solution - for example:

private void Change_Visible(Label toBeChanged)
{
    if (toBeChanged.Visible == false)
    {
        toBeChanged.Visible = true;
        toBeChanged.Refresh();
        return;
    }
    if (toBeChanged.Visible == true)
    {
        toBeChanged.Visible = false;
        toBeChanged.Refresh();
        return;
    }
}

I have not come to any conclusions. I am learning C# by myself and started just a few weeks ago, so maybe I am missing something obvious. Thanks for your help!

回答1:

The label won't actually become invisible to the user until its Parent redraws its background, painting over the pixels formerly drawn by the label control. This doesn't happen in your code, painting only occurs when the main thread goes idle and re-enters the message loop. It isn't idle, it is executing those "other things".

A workaround is to ask the parent to paint itself early:

myLabel.Visible = false;
this.Update();
//
// Do other things
//
myLabel.Visible = true;

Code that runs long enough to require feedback like this ought to be run in a worker thread instead. Use a BackgroundWorker or Task.

回答2:

Maybe try passing the label into your method by reference?

Change_Visible(ref myLabel);
//
// Do other things
//
Change_Visible(ref myLabel);

回答3:

i think the only problem with this code is that since the label is being refreshed in the UI thread it will wait for the paint event again.

for answer look at this link Why won't control update/refresh mid-process

回答4:

Just execute the following lines after your Visible/Enable changes and the job is done!

//Explicit call for render
this.Update();

来源：https://stackoverflow.com/questions/19470102/changing-label-visibility-with-a-method-why-wont-it-hide

标签

winforms

methods