Android TextWatcher监控EditText中的输入内容并限制其个数

布局中EditText在android布局中经常用到，对EditText中输入的内容也经常需要进行限制，我们可以通过TextWatcher去观察输入框中输入的内容，作个笔记。

主布局：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 android:orientation="vertical"
 android:layout_width="fill_parent"
 android:layout_height="fill_parent"
 >
<TextView android:id="@+id/tv"
 android:layout_width="fill_parent"
 android:layout_height="wrap_content"
 android:textColor="@android:color/white"
 android:ellipsize="marquee"
 android:focusable="true"
 android:marqueeRepeatLimit="marquee_forever"
 android:focusableInTouchMode="true"
 android:scrollHorizontally="true"  
 android:text="Please input the text:"
 />
<EditText android:id="@+id/ET"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:inputType="number"/>
</LinearLayout>

java代码：

package com.android.text;

import android.app.Activity;
import android.os.Bundle;
import android.text.Editable;
import android.text.TextWatcher;
import android.util.Log;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

public class TextWatcherDemo extends Activity {
 private TextView mTextView;
 private EditText mEditText;
 /** Called when the activity is first created. */
 @Override
 public void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   setContentView(R.layout.main);
   mTextView = (TextView)findViewById(R.id.tv);
   mEditText = (EditText)findViewById(R.id.ET);
   mEditText.addTextChangedListener(mTextWatcher);
 }
 TextWatcher mTextWatcher = new TextWatcher() {
   private CharSequence temp;
   private int editStart ;
   private int editEnd ;
   @Override
   public void beforeTextChanged(CharSequence s, int arg1, int arg2,
       int arg3) {
     temp = s;
   }

@Override
   public void onTextChanged(CharSequence s, int arg1, int arg2,
       int arg3) {
     mTextView.setText(s);
   }

@Override
   public void afterTextChanged(Editable s) {
     editStart = mEditText.getSelectionStart();
     editEnd = mEditText.getSelectionEnd();
     if (temp.length() > 10) {
       Toast.makeText(TextWatcherDemo.this,
           "你输入的字数已经超过了限制！", Toast.LENGTH_SHORT)
           .show();
       s.delete(editStart-1, editEnd);
       int tempSelection = editStart;
       mEditText.setText(s);
       mEditText.setSelection(tempSelection);
     }
   }
 };
}

来源：http://www.jianshu.com/p/4c5cba901f66