Android EditTexit设置最大长度 中文按2个字符计算

EditTexit限制字符长度大家都用过通常做法分2种：一种是在xml里给EditTexit设置maxLength属性，一种是在代码中添加过滤器LengthFilter，其实这两种方式最终都是通过设置过滤器的方式实现的，其中计算文字长度都是按照每个字符占1位来计算了，下面我们修改计算方式，以中文计为2个字符，英文计为1个字符方式计算。
重写了EditText类如下：

package com.yiming.demo;

import android.content.Context;
import android.text.InputFilter;
import android.text.Spanned;
import android.util.AttributeSet;
import android.util.Log;
import android.widget.EditText;

import java.lang.reflect.Field;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Created by Yiming on 2016/2/26.
 * 对最长字符控制的计算方式进行修改(InputFilter.LengthFilter的计算方式)
 * 中文和中文符号计为2个字符，英文、数字和英文符号计为1个字符。
 */
public class SuperEditTexit extends EditText {

    public SuperEditTexit(Context context) {
        super(context);
    }

    public SuperEditTexit(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    public void setFilters(InputFilter[] filters) {
        if(filters == null) {
            return;
        }
        int len = filters.length;
        if(len <= 0) {
            return;
        }
        for (int i=len-1; i>=0; i--) {
            InputFilter filter = filters[i];
            if(filter instanceof InputFilter.LengthFilter) {
                filters[i] = new SMLengthFilter(getMaxLength((InputFilter.LengthFilter) filter));
                break;
            }
        }
        super.setFilters(filters);
    }

    private int getMaxLength(InputFilter.LengthFilter filter) {
        int max = 0;
        Class clazz = (Class) filter.getClass();
        try {
            Field field = clazz.getDeclaredField("mMax");
            field.setAccessible(true);
            max = field.getInt(filter);
            Log.d("getMaxLength", "max=" + max);
        } catch (NoSuchFieldException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }
        return max;
    }

    public static class SMLengthFilter extends InputFilter.LengthFilter {

        int selfMax = 0;

        public SMLengthFilter(int max) {
            super(max);
            selfMax = max;
        }

        @Override
        public CharSequence filter(CharSequence source, int start, int end, Spanned dest, int dstart, int dend) {
//            Log.d("debug", source + "/" + start + "/" + end + "/" + dest.toString() + "/" + dstart + "/" + dend);
            int destLen = dend= getSequenceLength(dest);
            int sourceLen = getSequenceLength(source);
            int keep = selfMax - destLen;
            if (keep <= 0) {
                return "";
            } else if (keep >= sourceLen) {
                return null; // keep original
            } else {
                return subSequence(source, keep);
            }
        }

        private CharSequence subSequence(CharSequence source, int keep) {
            if(source == null || source.length()<=0) {
                return "";
            }
            int length = 0;
            char c;
            for (int i=0; i<source.length(); i++) {
                c = source.charAt(i);
                if(isChinese(c)) {
                    length += 2;
                } else {
                    length ++;
                }
                if(length > keep) {
                    if(i == 0) {
                        return "";
                    } else {
                        return source.subSequence(0, i);
                    }
                }
            }
            return source;
        }

        private int getSequenceLength(CharSequence cs) {
            int length = 0;
            if(cs == null || cs.length() == 0) return length;
            char c;
            for(int i=0; i<cs.length(); i++) {
                c = cs.charAt(i);
                if(isChinese(c)) {
                    length += 2;
                } else {
                    length ++;
                }
            }
            return length;
        }

        private 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;
        }

/*        private boolean isChinese(String s) {
            Pattern p= Pattern.compile("[\u4e00-\u9fa5]");
            Matcher m=p.matcher(s);
            if(m.matches()){
                return true;
            } else {
                return false;
            }
        }*/
    }
}

使用时只需使用旧的办法在xml中设置maxLength属性：

    <com.yiming.demo.SuperEditTexit
        android:id="@+id/et"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="10dp"
        android:layout_below="@id/tv"
        android:maxLength="5"
        />

或在代码中添加过滤器LengthFilter：

EditText et = (EditText) findViewById(R.id.et);
et.setFilters(new InputFilter[]{new InputFilter.LengthFilter(5)});

2种方式都可以实现。很简单…