输入组件获焦时实现提示文本的动态效果

问题现象
在使用TextInput和TextArea组件进行输入时，如何实现提示文字的动态效果？

背景知识
组件的某些通用属性变化时，可以通过animation属性动画实现渐变过渡效果，提升用户体验。
TextInput是HarmonyOS提供的一种单行文本输入框组件。
TextArea是多行文本输入框组件，当输入的文本内容超过组件宽度时会自动换行显示。
attributeModifier接口支持动态属性设置，支持开发者在属性设置时使用if/else语法，且根据需要使用多态样式设置属性。
解决方案
在Stack组件中创建Text提示文本和TextInput输入框。
创建TextModifier类，实现attributeModifier接口，该类中的applyNormalAttribute方法可根据对应的boolean类型的值动态修改对应组件的样式属性。
当点击TextInput组件时，执行onFocus方法，若文本值为空，将对应的TextModifier类的属性装载至该组件上，从而实现animation动画效果。
完整示例参考如下：

@Entry
@Component
struct TextInputTestOne {
// 定义状态变量
message: string = 'Hello World';
textAreaValue: string = '';
textInputValue: string = '';
selectValue: string = '';
@State modifierOne: TextModifier = new TextModifier(50, 150, 20);
@State modifierTwo: TextModifier = new TextModifier(50, 0, 20);
opacityOne: number = 0.3;
opacityTwo: number = 0.3;

build() {
Column() {
Column() {
Stack() {
Text('请在这输入文字：')
.fontSize(this.modifierOne.fontSize)
.textAlign(TextAlign.Start)
.fontColor(Color.Black)
.margin({ left: this.modifierOne.marginLeft, bottom: this.modifierOne.marginBottom })
.attributeModifier(this.modifierOne)
.width('100%')
.opacity(this.opacityOne)
// 实现动画效果
.animation({
duration: 300,
curve: Curve.Friction,
iterations: 1,
playMode: PlayMode.Normal
});
TextArea({ text: $$this.textAreaValue })
// 聚焦回调时间
.onFocus(() => {
if (this.textAreaValue === '') {
this.modifierOne.isFocus = true;
this.opacityOne = 1;
}
})
// 失焦回调事件
.onBlur(() => {
if (this.textAreaValue === '') {
this.modifierOne.isFocus = false;
this.opacityOne = 0.3;
}
})
.height('80%');
};
}
.justifyContent(FlexAlign.Center)
.height('30%')
.margin({ left: 20, right: 20 });

  Column() {  
    Stack() {  
      Text('请在这输入文字：')  
        .fontSize(this.modifierTwo.fontSize)  
        .fontColor(Color.Black)  
        .textAlign(TextAlign.Start)  
        .width('100%')  
        .margin({ left: this.modifierTwo.marginLeft, bottom: this.modifierTwo.marginBottom })  
        .attributeModifier(this.modifierTwo)  
        .opacity(this.opacityTwo)  
        // 实现动画效果  
        .animation({  
          duration: 300,  
          curve: Curve.Friction,  
          iterations: 1,  
          playMode: PlayMode.Normal  
        });  
      TextInput({ text: $$this.textInputValue })  
      // 聚焦回调时间  
        .onFocus(() => {  
          if (this.textInputValue === '') {  
            this.modifierTwo.isFocus = true;  
            this.opacityTwo = 1;  
          }  
        })  
        // 失焦回调事件  
        .onBlur(() => {  
          if (this.textInputValue === '') {  
            this.modifierTwo.isFocus = false;  
            this.opacityTwo = 0.3;  
          }  
        });  
    };  
  }  
  .justifyContent(FlexAlign.Center)  
  .height('30%')  
  .margin({ left: 20, right: 20 });  
}  
.height('100%')  
.width('100%');  

}
}

class TextModifier implements AttributeModifier<TextAttribute> {
isFocus: boolean | undefined = undefined;
marginLeft: number = 0;
marginBottom: number = 0;
fontSize: number = 0;

// 绑定属性
applyNormalAttribute(instance: TextAttribute): void {
if (this.isFocus) {
this.marginLeft -= 10;
this.marginBottom += 40;
this.fontSize -= 7;
instance
.fontSize(this.fontSize)
.margin({ left: this.marginLeft, bottom: this.marginBottom });
} else if (this.isFocus === false) {
this.marginLeft += 10;
this.marginBottom -= 40;
this.fontSize += 7;
instance
.fontSize(this.fontSize)
.margin({ left: this.marginLeft, bottom: this.marginBottom });
}
}

constructor(marginLeft: number, marginBottom: number, fontSize: number) {
this.marginLeft = marginLeft;
this.marginBottom = marginBottom;
this.fontSize = fontSize;
}
}
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