Android -- 重设字符并统计原字符以及修改字符的长度以及位置

package iflab.test;

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

public class firstActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        TextView myTextView = null; // 声明变量

        myTextView = (TextView) findViewById(R.id.myTextView); // 获取对象

        myTextView.addTextChangedListener(new TextWatcher() { // 添加监听器

                    @Override
                    public void afterTextChanged(Editable s) { // 文本改变后
                        // TODO Auto-generated method stub

                    }

                    @Override
                    public void beforeTextChanged(CharSequence s, int start,
                            int count, int after) {
                        // TODO Auto-generated method stub //文本改变前

                    }

                    @Override
                    public void onTextChanged(CharSequence s, int start,
                            int before, int count) {
                        // TODO Auto-generated method stub //文本改变时
                        Toast.makeText(
                                getApplicationContext(),
                                "原字符串共" + String.valueOf(before) + "个字符。"
                                        + "从第" + String.valueOf(start)
                                        + "个字符开始更改为字符串：" + s + "。共"
                                        + String.valueOf(count) + "字符。",
                                Toast.LENGTH_LONG).show(); // 显示提示信息
                    }
                });
        myTextView.setText("1234567890"); // 重设文本内容

    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <TextView
        android:id="@+id/myTextView"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="@string/hello" />

</LinearLayout>