事件处理

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原创最新推荐文章于 2026-06-25 11:30:52 发布 704 阅读 AI 写同款· GEO 优化 ›

Flutter之事件处理 在学习flutter的时候突然想到，flutter既然不像其他跨平台框架那样采用系统原生渲染，那么flutter就应该拥有自己的事件处理机制。本着好奇的心理，来对flutter的事件处理机制一窥究竟。 1、flutter事件传递事件都是由硬件收集起来的，然后传递给软件。那么在flutter中，事件的源头在哪尼？经过分析源码可以发现。在类window中，flutter通过方法onPointerD... 阅读详情

事件处理

以下的事件可由 JavaScript 发生:

onBlur
onChange
onClick
onFocus
onLoad
onMouseOver
onSelect
onSubmit
onUnload

onBlur event handler

A blur event occurs when a text or textArea field on a form loses focus. The onBlur event handler executes JavaScript code when a blur event occurs.
Applies to

selection, text, textArea
Examples

xxx Examples to be supplied.

onChange event handler

A change event occurs when a selection, text, or textArea field loses focus and its value has been modified. The onChange event handler executes JavaScript code when a change event occurs.
Use the onChange event handler to validate data after it is modified by a user.
Applies to

selection, text, textArea
Examples

xxx Examples to be supplied.

onClick event handler

For button or radioButton, JavaScript code to run when a button is clicked. For checkbox, JavaScript code to run when user checks or unchecks an item.

Applies to

button, checkbox, radioButton, link, reset, submit
Examples

For example, suppose you have created a JavaScript function called compute(). You can execute the compute() function when the user clicks a button by calling the function in the onClick event handler, as follows:
```
<INPUT TYPE="button" VALUE="Calculate" onClick="compute(this.form)">
```
In the above example, the keyword this refers to the current object; in this case, the Calculate button. The construct this.form refers to the form containing the button.
For another example, suppose you have created a JavaScript function called pickRandomURL() that lets you select a URL at random. You can use the onClick event handler of an anchor to dynamically specify a value for the HREF attribute of the anchor, as shown in the following example:
```
  &lt;A HREF="" onClick="this.href=pickRandomURL();" onMouseOver="window.status='Pick a random URL'; return true"&gt; Go!&lt;/A&gt;
 
```
In the above example, the onMouseOver event handler specifies a custom message for the Navigator status bar when the user places the mouse pointer over the Go! anchor. As this example shows, you must return true to set the window.status property in the onMouseOver event handler.

onFocus event handler

Executed when input focus enters the field, either by tabbing in or by clicking but not selecting in the field.
Applies to

selection, text, textArea
Examples

xxx Examples to be supplied.

onLoad event handler

A load event occurs when Navigator finishes loading a window or all frames within a FRAMESET. The onLoad event handler executes JavaScript code when a load event occurs.
Use the onLoad event handler within either the <BODY> or the <FRAMESET> tag, for example, <BODY onLoad="...">.
Applies to

document, window
Examples

xxx Examples to be supplied.
See also

onUnload event handler

onMouseOver event handler

Executes when the mouse pointer is over an object. You must return true if you want to set the window.status property with the onMouseOver event handler.
Applies to

link
Examples

By default, the HREF value of an anchor displays in the status bar at the bottom of the Navigator when a user places the mouse pointer over the anchor. In the following example, the onMouseOver event handler provides the custom message "Click this if you dare."
```
  &lt;A HREF="http://home.netscape.com/" onMouseOver="window.status='Click this if you dare!'; return true"&gt; Click me&lt;/A&gt;
 
```
See onClick for an example of using onMouseOver when the anchor HREF attribute is set dynamically.

onSelect event handler

A select event occurs when a user selects some of the text within a text or textArea field. The onSelect event handler executes JavaScript code when a select event occurs.
Applies to

text, textArea
Examples

xxx Examples to be supplied.

onSubmit event handler
Specifies the JavaScript code to run when a user attempts to submit a form. Return true to allow the form to be submitted; return false to prevent the form from being submitted.
Applies to

form
Examples

In the following example, the onSubmit event handler evaluates the data being submitted to test if it is legal. If the data is legal, the form is submitted; otherwise, the form is not submitted.
```
  form.onSubmit= "if badFormData(this.form) { return false; } else { return true; }"
 
```
onUnload event handler

An unload event occurs when you exit a document. The onUnload event handler executes JavaScript code when an unload event occurs.
Use the onUnload event handler within either the <BODY> or the <FRAMESET> tags, for example, <BODY onUnload="...">.
Applies to

document, window
Examples

xxx Examples to be supplied.
See also

onLoad event handler