使用EditText的addTextChangedListener(TextWatcher watcher)方法对EditText实现监听，TextWatcher是一个接口类，所以必须实现TextWatcher里的抽象方法：
当EditText里面的内容有变化的时候，，触发TextChangedListener事件，就会调用TextWatcher里面的抽象方法。布局：<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android=""android:orientation="vertical"android:layout_width="fill_parent"android:layout_height="fill_parent" ><EditTextandroid:id="@+id/main_et"android:layout_width="fill_parent"android:layout_height="wrap_content" /> <TextViewandroid:id="@+id/main_tv"android:layout_width="fill_parent"android:layout_height="wrap_content" /> </LinearLayout>一、实现监听文本框字数，提示还能输入多少个字符MainActivity：package chay.mian;import android.app.Activity;import android.os.Bundle;import android.text.Editable;import android.text.TextWatcher;import android.view.View;import android.widget.EditText;import android.widget.TextView;public class MainActivity extends Activity {private EditText editText;private TextView tip;private final int charMaxNum = 10; // 允许输入的字数@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);init();}private void init() {editText = (EditText) findViewById(R.id.main_et);editText.addTextChangedListener(new EditChangedListener());tip = (TextView) findViewById(R.id.main_tv);tip.setText("0/"+charMaxNum);}class EditChangedListener implements TextWatcher {private CharSequence temp; // 监听前的文本private int editStart; // 光标开始位置private int editEnd; // 光标结束位置// 输入文本之前的状态@Overridepublic void beforeTextChanged(CharSequence s, int start, int count,int after) {temp = s;}// 输入文字中的状态，count是一次性输入字符数@Overridepublic void onTextChanged(CharSequence s, int start, int before, int count) {//if (charMaxNum – s.length() <= 5) {//tip.setText("还能输入" + (charMaxNum – s.length()) + "字符");//}tip.setText((s.length()) + "/" + charMaxNum);}// 输入文字后的状态@Overridepublic void afterTextChanged(Editable s) {/** 得到光标开始和结束位置 ,超过最大数后记录刚超出的数字索引进行控制 */editStart = editText.getSelectionStart();editEnd = editText.getSelectionEnd();if (temp.length() > charMaxNum) {//Toast.makeText(getApplicationContext(), "最多输入10个字符", Toast.LENGTH_SHORT).show();s.delete(editStart – 1, editEnd);editText.setText(s);editText.setSelection(s.length());}}};}
二、数据类型检验，当输入不是整型数字的时候，会立刻弹出输入框，提示改正MainActivity：
package chay.mian;import android.app.Activity;import android.app.AlertDialog;import android.content.DialogInterface;import android.os.Bundle;import android.text.Editable;import android.text.TextWatcher;import android.util.Log;import android.widget.EditText;import android.widget.TextView;public class MainActivity extends Activity {private EditText editText;private TextView tip;String str;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_mian);init();}private void init() {editText = (EditText) findViewById(R.id.mian_et);editText.addTextChangedListener(new EditChangedListener());tip = (TextView) findViewById(R.id.mian_tv);tip.setText("请输入整型数字");}class EditChangedListener implements TextWatcher {// 输入文本之前的状态@Overridepublic void beforeTextChanged(CharSequence s, int start, int count, int after) {Log.d("TAG", "beforeTextChanged—————>");}// 输入文字中的状态，count是一次性输入字符数@Overridepublic void onTextChanged(CharSequence s, int start, int before, int count) {Log.d("TAG", "onTextChanged—————>");}// 输入文字后的状态@Overridepublic void afterTextChanged(Editable s) {Log.d("TAG", "afterTextChanged—————>");str = editText.getText().toString();try {//if ((editText.getText().toString()) != null)Integer.parseInt(str);} catch (Exception e) {showDialog();}}};private void showDialog() {AlertDialog dialog;AlertDialog.Builder builder = new AlertDialog.Builder(this);builder.setTitle("消息").setIcon(android.R.drawable.stat_notify_error);builder.setMessage("你输出的整型数字有误，请改正");builder.setPositiveButton("确定", new DialogInterface.OnClickListener() {@Overridepublic void onClick(DialogInterface dialog, int which) {// TODO Auto-generated method stub}});dialog = builder.create();dialog.show();}}
美好的生命应该充满期待惊喜和感激
