本文详细介绍了Android中TextWatcher监听器的工作原理及其两个关键方法：beforeTextChanged和onTextChanged的作用。beforeTextChanged方法会在文本变化前调用，而onTextChanged则在文本变化后调用。
TextWatcher中的参数
- beforeTextChanged
@Override
public void beforeTextChanged(CharSequence s, int start, int count, int after) {
}This method is called to notify you that, within s, the count characters beginning at start are about to be replaced by new text with length after. It is an error to attempt to make changes to s from this callback.
字符串s中，从start开始的count个字符 将会 被长度为after的字符串替换
- onTextChanged
@Override
public void onTextChanged(CharSequence s, int start, int before, int count) {
}This method is called to notify you that, within s, the count characters beginning at start have just replaced old text that had length before. It is an error to attempt to make changes to s from this callback.
字符串s中，从start开始的count个字符 替换了 长度为before的字符串
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