harmony 鸿蒙Basic Usage of Custom Components

2022-08-09
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Basic Usage of Custom Components

Custom components are existing components encapsulated based on service requirements. A custom component can be invoked multiple times in a project to improve the code readability. You can import a custom component to the host page through element as shown in the following code snippet:

<element name='comp' src='../common/component/comp.hml'></element>
<div>
  <comp prop1='xxxx' @child1="bindParentVmMethod"></comp>
</div>

The following is an example of using a custom component with if-else, which displays comp1 when showComp1 is set to true and displays comp2 otherwise.

<element name='comp1' src='../common/component/comp1/comp1.hml'></element>
<element name='comp2' src='../common/component/comp2/comp2.hml'></element>
<div>
  <comp1 if="{{showComp1}}" prop1='xxxx' @child1="bindParentVmMethodOne"></comp1>
  <comp2 else prop1='xxxx' @child1="bindParentVmMethodTwo"></comp2>
</div>

The name attribute indicates the custom component name (optional), which is case-insensitive and is in lowercase by default. The src attribute indicates the .hml file path (mandatory) of the custom component. If name is not set, the .hml file name is used as the component name by default.

Custom Events

To bind an event to a custom child component, use the (on|@)event-name=“bindParentVmMethod” syntax. this.$emit(‘eventName’, { params: ‘passedParameters’ }) is used in the child component to trigger the event and pass parameters to the parent component. The parent component then calls the bindParentVmMethod API and receives parameters passed by the child component.

NOTE

For child component events that are named in camel case, convert the names to kebab case when binding the events to the parent component. For example, use \@children-event in the parent component instead of childrenEvent used in the child component.

Example 1 with parameters passed

The following example describes how to define a child component comp:

<!-- comp.hml -->
<div class="item">  
   <text class="text-style" onclick="childClicked">Click here to view the hidden text.</text> 
   <text class="text-style" if="{{showObj}}">hello world</text> 
</div>

/* comp.css */
.item {  
  width: 700px;   
  flex-direction: column;   
  height: 300px;   
  align-items: center;   
  margin-top: 100px;  
} 
.text-style { 
  font-weight: 500; 
  font-family: Courier; 
  font-size: 40px;
}

// comp.js
export default { 
  data: {  
    showObj: false,  
  },  
  childClicked () {  
    this.$emit('eventType1'); 
    this.showObj = !this.showObj;  
  },  
}

The following example describes how to import comp to the parent component:

<!-- xxx.hml --> 
<element name='comp' src='../common/component/comp.hml'></element>  
<div class="container">  
  <comp @event-type1="textClicked"></comp>  
</div>

/* xxx.css */
.container {  
  background-color: #f8f8ff;  
  flex: 1;  
  flex-direction: column;  
  align-content: center; 
}

// xxx.js
export default {    
  textClicked () {} 
}

Example 2 with no parameters passed

The following example describes how to define a child component comp:

<!-- comp.hml -->
<div class="item">  
   <text class="text-style" onclick="childClicked">Click here to view the hidden text.</text> 
   <text class="text-style" if="{{ showObj }}">hello world</text> 
</div>

// comp.js
export default { 
  childClicked () {
    this.$emit('eventType1', { text: 'Receive the parameters from the child component.' });
    this.showObj = !this.showObj;
  },
}

In the following example, the child component passes the text parameter to the parent component, and the parent component obtains the parameter through e.detail:

<!-- xxx.hml -->
<element name='comp' src='../common/comp/comp.hml'></element>
<div class="container">  
   <text>Parent component: {{text}}</text> 
   <comp @event-type1="textClicked"></comp>  
</div>

// xxx.js
export default { 
  data: {
    text: 'Start'
  },
  textClicked (e) {
    this.text = e.detail.text;
  },
}

EventParameters

Custom Component Data

In the JS file of a custom component, you can define, pass, and process data by declaring fields such as data, props, and computed. For details about how to use props and computed, see Data Transfer and Processing.

Table 1 Custom component data

Name	Type	Description
data	Object \|Function	Data model of the page. If the attribute is of the function type, the return value must be of the object type. The name cannot start with a dollar sign ($) or underscore (_). Do not use reserved words (for, if, show, and tid). Do not use this attribute and private or public at the same time.
props	Array \|Object	Used for communication between components. This attribute can be passed to components through <tag xxxx=‘value’>. A props name must be in lowercase and cannot start with a dollar sign ($) or underscore (_). Do not use reserved words (for, if, show, and tid) in the name. Currently, props does not support functions.
computed	Object	Used for pre-processing for reading and setting parameters. The result is cached. The name cannot start with a dollar sign ($) or underscore (_). Do not use reserved words.