方法一：

EditText標籤下增加以下屬性：

android:maxLength="18"
android:digits="1234567890qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM"

通過TextWatcher實現，更加靈活。

首先，自定義一個TextWatcher：

public static class IDNumberTextWatcher implements android.text.TextWatcher {
        /**
         * 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.
         */
        @Override
        public void beforeTextChanged(CharSequence s, int start, int count, int after) {

        }
        /**
         * This method is called to notify you that, within <code>s</code>,
         * the <code>count</code> characters beginning at <code>start</code>
         * have just replaced old text that had length <code>before</code>.
         * It is an error to attempt to make changes to <code>s</code> from
         * this callback.
         */
        @Override
        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.
         */
        @Override
        public void afterTextChanged(Editable s) {
            String temp = s.toString();
            Log.d(TAG, "temp=" + temp);
            if (!TextUtils.isEmpty(temp)) {
                if (temp.length() <= 18) {
                    String tem = temp.substring(temp.length() - 1, temp.length());
                    char[] temC = tem.toCharArray();
                    int mid = temC[0];
                    // Number
                    if(mid>=48&&mid<=57){
                        return;
                    }
                    // Upper case
                    if(mid>=65&&mid<=90){
                        return;
                    }
                    // Lower case
                    if(mid>=97&&mid<=122){
                        return;
                    }
                }
                else {
		    Log.d(TAG, "current input length is over 18");
 		}
 		s.delete(temp.length()-1, temp.length());
 	    }
 		else {
 		Log.d(TAG, "current input is null");
 	    }
 	}
}
 

idNumEt.addTextChangedListener(new IDNumberTextWatcher());