簡述：Android中EditText等控制元件監聽文字內容的更改使用的是TextWatcher介面，但是官方文件對該介面中方法的引數說明很模糊，在此記錄下對方法引數的認識（隨認識的增加逐步完善）

public interface TextWatcher extends NoCopySpan {
    /**
     * This method is called to notify you that, within <code>s</code>,
     * the <code>count</code> characters beginning at <code>start</code>
     * are about to be replaced by new text with length <code>after</code>.
     * It is an error to attempt to make changes to <code>s</code> from
     * this callback.
     */
 

    public void beforeTextChanged(CharSequence s, int start,
                                  int count, int after);
    /**
     * 文字更改後的回撥（使用時發現，小米手機，貼上時前後都會預設加一個空格，
     * 造成引數的數字不準確，不知其他手機有無此情況，此處以鍵盤輸入或刪除為
     * 準。）
     * @param s
     *        更改以後現存的字串
     * @param start
     *        新增字元：該值為新增字元所在的下標
     *        刪除字元：該值為刪掉字元所在的先
     * @param
 
 before
     *        新增字元：該值為0
     *        刪除字元：該值為刪掉的字元數
     * @param count
     *        新增字元：值為新增字元數
     *        刪除字元：值為0
     */
    public void onTextChanged(CharSequence s, int start, int before, int count);

    /**
     * This method is called to notify you that, somewhere within
     * <code>s</code>, the text has been changed.
     * It is legitimate to make further changes to <code>s</code> from
     * this callback, but be careful not to get yourself into an infinite
     * loop, because any changes you make will cause this method to be
     * called again recursively.
     * (You are not told where the change took place because other
     * afterTextChanged() methods may already have made other changes
     * and invalidated the offsets.  But if you need to know here,
     * you can use {@link Spannable#setSpan} in {@link #onTextChanged}
     * to mark your place and then look up from here where the span
     * ended up.
     */
 

    public void afterTextChanged(Editable s);