Suggestions on using the hidden attribute of components in WeChat mini programs

1, let’s first look at an author’s experiment

It is mentioned in WeChat’s official documentation that hidden is a property that all components have. In actual coding, it was found that its performance is similar to The description doesn't quite fit the description.

For example, the following layout:

You will find that hidden does not take effect.

After experiments, it was found that the hidden element only takes effect on block layout, so the culprit in this code that causes hidden to not take effect is display:flex. Just remove this.

In order to verify what the author said, I turned over the css document and practiced all possible values ​​of the display style one by one:

Value Description

none This element will not be displayed .

block This element will be displayed as a block-level element, with line breaks before and after this element.

inline Default. This element will be displayed as an inline element with no line breaks before or after the element.

inline-block Inline block element. (New value in CSS2.1)

list-item This element will be displayed as a list.

run-in This element will be displayed as a block-level element or an inline element depending on the context.

compact There is a value compact in CSS, but it has been removed from CSS2.1 due to lack of widespread support.

marker There is a value marker in CSS, but it has been removed from CSS2.1 due to lack of widespread support.

table This element will be displayed as a block-level table (similar to ), with line breaks before and after the table.

inline-table This element will be displayed as an inline table (similar to ), with no line breaks before and after the table.

table-row-group This element will be displayed as a group of one or more rows (similar to ).

table-header-group This element will be displayed as a group of one or more rows (similar to ).

table-footer-group This element will be displayed as a group of one or more rows (similar to ).

table-row This element will be displayed as a table row (similar to ).

table-column-group This element will be displayed as a group of one or more columns (similar to ).

table-column This element will be displayed as a cell column (similar to)

table-cell This element will be displayed as a table cell (similar to and)

table -caption This element will be displayed as a table title (similar)

inherit Specifies that the value of the display attribute should be inherited from the parent element.

Changing to any value, except none, as well as the abandoned compact and marker, will not work.

So, WHY?

Let’s continue reading the original text first~

2, use display:none to control the display and concealment

What if you must use flex layout?

In fact, the purpose of using hidden here is just to hide this layout. Display:none can also hide it. Here you can use a tricky method to dynamically set the display attribute. The example is as follows:

The hideview here is a variable in the corresponding js and is dynamically controlled by js.

Afterword: hidden hides the layout. Although it is hidden, it still takes up space. display:none hides and does not occupy space.

3. Regarding the difference between wx:if and hidden

, how should we understand the last sentence? Doesn’t it take up interface space?

no!

What the author wants to express, it is speculated that although hidden hides the view component, the component will still be rendered; display:none and hidden=true have the same effect, and display:none will still render the component.

If you want not to render unnecessary components, use conditional rendering: wx:if

wx:if vs hidden

Because the template in wx:if may also Contains data binding, so when the conditional value of wx:if switches, the framework has a local rendering process, because it will ensure that the conditional block is destroyed or re-rendered when switching.

At the same time, wx:if is also lazy. If the initial rendering condition is false, the framework does nothing and starts partial rendering when the condition becomes true for the first time. In contrast, hidden is much simpler. The component will always be rendered, and it is just a simple control of display and hiding. Generally speaking, wx:if has a higher switching cost and hidden has a higher initial rendering cost. Therefore, if frequent switching is required, hidden is better, and wx:if is better if conditions are unlikely to change at runtime. (Reposted from the WeChat document)

4, Regarding the answer to the WHY above

Back to the question of the red statement above, it cannot be said that the problem is caused by display:flex. It's caused by the programmers themselves.

Look at the rendering of view style:

The applet first renders the component name style (i.e. view), and then renders the style attribute style. (Not tested on ios and android phones)

So it is easy to understand. It is not that the hidden attribute of the WeChat applet does not take effect, but the hidden attribute of the applet is achieved by adding a display:none to the name style, see the red arrow above.

Then, the programmer set a display:block in the style attribute, directly overriding the settings of the mini program. So, how could it possibly work? Isn’t this the fault of the programmers themselves?

So, why is it easier to use the obsolete compact and marker?

Because these two do not exist in the mini program at all. Setting them equals no setting.

5. Regarding the value of the hidden attribute, it doesn’t matter if you don’t set it. Setting it is useless.

In addition, there is one thing about the value of the hidden attribute, like the above code:

hidden="true"

In fact, setting it to hidden="false", or "0", or any other value is equivalent, and the result is true.

This is not only true for the hidden attribute, but also for all Boolean attributes in the applet component. The completion can be used like this:

Just write this hidden attribute.

6. It is recommended not to use the hidden attribute. It is a useless and stupid attribute.

So, everyone has seen it:

1. Use display :none can achieve the same effect as hidden

2. No matter how the value of hidden is set, the result is true. You don’t even have to do dynamic binding. You can only use wx:if for conditional rendering

3, having said that, if we have to use lazy wx:if conditional rendering, why should I use hidden?

wx: if rendering is lazy rendering, it only renders when needed. The disadvantage is that it is repeatedly destroyed and rebuilt, which consumes electricity! (It’s a waste of mobile phone CPU and really wastes electricity)

And display:none just switches the display, and the things that have been rendered are still there.

To summarize, if it is not a long list rendering, it is recommended to use display:none to control the display and hiding. If it is a long list rendering, use conditional rendering.

Hidden is a completely stupid attribute with no use. It will only confuse programmers.

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