EditText限制输入字符串长度

参考博文链接： http://www.cnblogs.com/jason-star/archive/2013/01/01/2841596.html

EditText限制字符串输入长度的改动办法：

1、在 xml 文件中设置文本编辑框属性作字符数限制

    如：android:maxLength="10" 即限制最大输入字符个数为10

2、在代码中使用InputFilter 进行过滤

    //editText.setFilters(new InputFilter[]{new InputFilter.LengthFilter(20)}); 即限定最大输入字符数为20

    也可在InputFilter里添加新方法
  

 public static class AdnNameLengthFilter implements InputFilter
			    {
			        private int nMax;
			        public  CharSequence filter (CharSequence source, int start, int end, Spanned dest, int dstart, int dend){
			            if((dest.toString().getBytes(Charset.defaultCharset()).length <= 32 && dest.toString().length() > 10)
			                || (source.toString().getBytes(Charset.defaultCharset()).length <= 32 && source.toString().length() > 10)){
			                nMax = 30;
			            }else{
			                nMax = 10;
			            }

			                int keep = nMax - (dest.length() - (dend - dstart));

			                if (keep <= 0) {
			                    return "";
			                } else if (keep >= end - start) {
			                    return null; // keep original
			                } else {
			                     keep += start;
			                     if (Character.isHighSurrogate(source.charAt(keep - 1))) {
			                        --keep;
			                        if (keep == start) {
			                          return "";
			                        }
			                     }
			                     return source.subSequence(start, start + keep);
			                }
			        }
			    }

根据输入字符串或者显示字符串的字节长度和字符串长度判断，因为汉字在android中一个字符占3个字节，EditText输入最长为32个字节所以汉字只能输入10个字符。
3、利用 TextWatcher 进行监听

package com.example.test12;import android.os.Bundle;import android.R.menu;import android.app.Activity;import android.text.Editable;import android.text.TextWatcher;import android.util.Log;import android.view.Menu;import android.widget.EditText;public class MainActivity extends Activity implements TextWatcher{        EditText mEditText;    public static final int MAX_BYTE_LENGTH=30;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        mEditText=(EditText) findViewById(R.id.edittext);        mEditText.addTextChangedListener(this);    }    @Override    public boolean onCreateOptionsMenu(Menu menu) {        // Inflate the menu; this adds items to the action bar if it is present.        getMenuInflater().inflate(R.menu.main, menu);        return true;    }    @Override    public void afterTextChanged(Editable s) {        // TODO Auto-generated method stub            }    @Override    public void beforeTextChanged(CharSequence s, int start, int count,            int after) {        // TODO Auto-generated method stub        String text=mEditText.getText().toString();        int inputByteLength=0;        for(int i=0;i<text.length();i++){            inputByteLength+=text.substring(i, i+1).getBytes().length;        }                int beforByteLength=0;        String beforString = s.toString();        for(int i=0;i<beforString.length();i++){            beforByteLength+=beforString.substring(i, i+1).getBytes().length;        }                if(inputByteLength > MAX_BYTE_LENGTH){            mEditText.setText(s);            mEditText.setSelection(mEditText.getText().toString().length());            return;        }                Log.d("TXX","beforeTextChanged-S:"+s);        Log.d("TXX","beforeTextChanged-start:"+start);        Log.d("TXX","beforeTextChanged-count:"+count);        Log.d("TXX","beforeTextChanged-after:"+after);    }    @Override    public void onTextChanged(CharSequence s, int start, int before, int count) {        // TODO Auto-generated method stub        String text=mEditText.getText().toString();        int maxStringLength=0;        int inputByteLength=0;        for(int i=0;i<text.length();i++){            inputByteLength+=text.substring(i, i+1).getBytes().length;            if(inputByteLength > MAX_BYTE_LENGTH){                maxStringLength=i;            }        }        if(inputByteLength > MAX_BYTE_LENGTH){            mEditText.setText(s.subSequence(0, maxStringLength));            mEditText.setSelection(mEditText.getText().toString().length());            return;        }    }}

输入的字符串限制最大为30个字节，遍历输入的字符串字符得出字节长度如果大于MAX_BYTE_LENGTH最大字节数，则返回从0到i的字符串。
在对应的Activity中调用TextWather

package cie.textEdit;  
import android.app.Activity; 
import android.os.Bundle; 
import android.text.InputFilter; 
import android.widget.EditText; 

publicclass TextEditActivity extends Activity { 
    /** Called when the activity is first created. */ 
    @Override 
    publicvoid onCreate(Bundle savedInstanceState) { 
        super.onCreate(savedInstanceState); 
        setContentView(R.layout.main); 

        EditText editText = (EditText) findViewById(R.id.entry); 
        editText.addTextChangedListener(new MaxLengthWatcher(10, editText)); 

    } 
}