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);
            }
        }
    };
}