Adding and Selecting New Items in Polymer's iron-list: A Comprehensive Guide
Adding new items to a list and automatically selecting them is a common requirement in web applications. Polymer's iron-list component, designed for efficiently handling large datasets, can make this process seamless. However, the exact implementation might not be immediately clear. This article aims to clarify how to add items to an iron-list and select the newly added item, providing a practical solution and insights into the underlying mechanisms.
Scenario: Adding and Selecting a New Todo
Let's imagine a simple to-do list application built with Polymer. We have an iron-list displaying existing tasks, and we need to add a new task, automatically selecting it for immediate editing. Here's a basic example of how this could be implemented:
<template is="dom-bind">
<style>
#new-task {
margin-bottom: 10px;
}
</style>
<div id="new-task">
<input type="text" id="taskInput" placeholder="Add new task" value="{{newTask}}">
<button on-click="addNewTask">Add</button>
</div>
<iron-list items="{{tasks}}" as="task">
<template>
<div class="task-item" on-tap="selectTask" data-task-id="{{task.id}}">
{{task.name}}
</div>
</template>
</iron-list>
</template>
<script>
Polymer({
is: 'todo-app',
properties: {
tasks: {
type: Array,
value: []
},
newTask: {
type: String,
value: ''
},
selectedTaskId: {
type: Number,
value: null
}
},
addNewTask: function() {
let newId = this.tasks.length > 0 ? Math.max(...this.tasks.map(t => t.id)) + 1 : 1;
this.push('tasks', { id: newId, name: this.newTask });
this.newTask = ''; // Clear the input field
this.selectTask({ detail: { taskId: newId } }); // Select the newly added task
},
selectTask: function(event) {
this.selectedTaskId = parseInt(event.target.dataset.taskId, 10);
}
});
</script>
Explanation:
-
addNewTaskFunction:- Generates a unique ID for the new task.
- Uses
pushto add the new task to thetasksarray. - Clears the input field.
- Calls
selectTaskwith the new task's ID to trigger selection.
-
selectTaskFunction:- Retrieves the task ID from the clicked element's
data-task-idattribute. - Updates the
selectedTaskIdproperty, which can be used to highlight or modify the selected task.
- Retrieves the task ID from the clicked element's
-
iron-listConfiguration:- The
items="{{tasks}}"binding dynamically updates theiron-listwith thetasksarray. as="task"assigns the current item to thetaskvariable within the template.
- The
-
Task Item Template:
- The
on-tap="selectTask"attribute triggers theselectTaskfunction when a task item is clicked. - The
data-task-id="{{task.id}}"attribute stores the task ID for retrieval.
- The
Important Considerations:
- Performance:
iron-listis optimized for large datasets, but adding items efficiently depends on the size of your list and the complexity of your item template. - Focus Management: If you are focusing on the new item for editing, you might need to explicitly set the focus on the corresponding element using JavaScript after adding the item.
iron-listRefresh: For very large lists, theiron-listmight not automatically refresh after adding an item. To ensure proper rendering, you can trigger a refresh using therefreshmethod on theiron-listelement after updating thetasksarray.
Example with Focus Management:
addNewTask: function() {
// ... (add new task code) ...
this.selectTask({ detail: { taskId: newId } });
// Set focus on the newly added task
let newItem = this.$('div[data-task-id="' + newId + '"]');
if (newItem) {
newItem.focus();
}
}
This example demonstrates setting focus on the newly added task element for immediate editing.
Conclusion:
By understanding how to leverage iron-list's features, you can efficiently add new items to your list and select them programmatically. This approach provides a robust foundation for building interactive and dynamic list-based applications using Polymer.
Further Resources:
