EditText輸入字符數控制

爲EditText設置Filter

		EditText et = (EditText) view.findViewById(R.id.name_et);
		InputFilter[] filters = {new AdnNameLengthFilter()};
		name_et.setFilters(filters);

其中，AdnNameLengthFilter繼承自InputFilter

import android.text.InputFilter;
import android.text.Spanned;
/**
 * EditText設置最大可輸入字符數（中文佔2字符，英文佔1字符）
 * @author Administrator
 *
 */
public class AdnNameLengthFilter implements InputFilter {
	// 最大字符數
	int max = 10;
	/**
	 * CharSequence source,  //輸入的文字
	 * int start  //開始位置
	 * int end  //結束位置
	 * Spanned dest //當前顯示的內容
	 * int dstart  //當前開始位置
	 * int dend //當前結束位置
	 */
	@Override
	public CharSequence filter(CharSequence source, int start, int end,
			Spanned dest, int dstart, int dend) {
		int source_count = countChinese(source.toString());//剛輸入的字符中所含中文字符數
		int dest_count = countChinese(dest.toString());//已存在字符中所含中文字符數
		int keep = max - dest_count - (dest.length() - (dend - dstart)) ;//還能輸入的字符數
		
		if (keep <= 0) {//字符數滿
			return "";
		} else if (keep - source_count >= end - start ) {//加入新字符後字符數未滿
			return null; // keep original
		} else {//加入新字符後字符數超
			char[] ch = source.toString().toCharArray();
			int k = keep;
			keep = 0;
			for(int i = 0; i < ch.length; i++){
				if(isChinese(ch[i])){
					k = k - 2;
				}else{
					k--;
				}
				keep ++ ;
				if(k <= 0){
					break;
				}
			}
			return source.subSequence(start, start + keep);
		}
	}

	/**
	 * 判斷是否爲中文
	 * @param c
	 * @return
	 */
	private static final boolean isChinese(char c) {
		Character.UnicodeBlock ub = Character.UnicodeBlock.of(c);
		if (ub == Character.UnicodeBlock.CJK_UNIFIED_IDEOGRAPHS
				|| ub == Character.UnicodeBlock.CJK_COMPATIBILITY_IDEOGRAPHS
				|| ub == Character.UnicodeBlock.CJK_UNIFIED_IDEOGRAPHS_EXTENSION_A
				|| ub == Character.UnicodeBlock.GENERAL_PUNCTUATION
				|| ub == Character.UnicodeBlock.CJK_SYMBOLS_AND_PUNCTUATION
				|| ub == Character.UnicodeBlock.HALFWIDTH_AND_FULLWIDTH_FORMS) {
			return true;
		}
		return false;
	}

	/**
	 * 計算字符串中中文字符數
	 * @param strName
	 * @return
	 */
	int countChinese(String strName){
		int count = 0;
		char[] ch = strName.toCharArray();
		for (int i = 0; i < ch.length; i++) {
			char c = ch[i];
			if (isChinese(c)) {
				count ++;
			}
		}
		return count;
	}

}