Android自定义View系列之可伸缩的TextView

经常访问我博客的同学应该注意到了我的博客大部分是关于分析Android系统原理的，很少涉及应用层的知识，但是想要开发一个用户欢迎的App，没有一个炫酷的UI肯定是不行的，就好比一个人想成为武林高手仅仅修炼内功是不行的，必须内功和外功同时修炼才能成为真正的武林高手。很多人在开发Android的App过程中有这样的感觉，我不用学习Android系统原理照样可以进行Android开发，而且可以做出非常炫酷的效果，确实是这样的 ，因为对于一款App，它的大部分需求无非就是请求数据然后展示数据，至于一些炫酷的UI控件网上有很多开源的，所以我们不用懂Android系统的原理同样可以进行App开发，相信你自己也发现了，长期做这样的工作，你的技术是永远得不到提升的，当你使用别人开源的炫酷的控件时，你并不知道别人是怎么实现的，即使你有兴趣看别人的实现方法，如果你不懂Android系统原理，估计你也看不懂别人为什么要这么做。所以从今天起的半年时间，我会将学习重点放在应用层的开发，主要是自定义View和炫酷的动画的学习上。

该自定义View具备如下特性：

1. 当显示的内容没有2行(可以通过属性配置)时，和普通的TextView一样

2. 当显示的内容大于2行时，仅仅显示两行，并且没有显示完的内容使用省略号代替，并显示向下箭头表示还有内容没有显示全

3. 当用户点击TextView时，内容全部展开，当用户再次点击时，TextView又变为压缩模式

下面我们开始代码实现，正如上面所说，此View支持自定义属性，所以我们先要定义attrs.xml文件，如何编写attrs.xml文件网上有很多教程，我这里就不在说了。

<?xml version="1.0" encoding="utf-8"?><resources>
    <declare-styleable name="ExpandTextView">
        <attr name="textcolor" format="color"></attr>
        <attr name="textsize" format="dimension"></attr>
        <attr name="icon" format="reference"></attr>
        <attr name="lines" format="integer"></attr>
        <attr name="text" format="string"></attr>
    </declare-styleable></resources>12345678910

这几个属性的意义如下：

• textcolor : 字体颜色

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