通过TextWatcher去观察输入框中输入的内容以及输入字符个数

　　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);

            }

        }

    };

}