<?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"    >
<!--注意名称 -->
<com.marine.study.LineEditText     android:id="@+id/myEdit"    android:layout_width="fill_parent"     android:layout_height="wrap_content"     style="?android:attr/textViewStyle"     android:background="@null"    android:textColor="@null"
/>
</LinearLayout> 

//请在这里添加您的包名
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.widget.EditText;  public class LineEditText extends EditText {  private Paint mPaint;  /** * @param context * @param attrs */  public LineEditText(Context context, AttributeSet attrs) {  super(context, attrs);  // TODO Auto-generated constructor stub  mPaint = new Paint();  mPaint.setStyle(Paint.Style.STROKE);  mPaint.setColor(Color.BLUE);  }  @Override  public void onDraw(Canvas canvas)  {  super.onDraw(canvas);  //      画底线  canvas.drawLine(0,this.getHeight()-1,  this.getWidth()-1, this.getHeight()-1, mPaint);  }
}  

import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.os.Bundle;
import android.text.InputFilter;
import android.util.AttributeSet;
import android.widget.EditText;  public class LineEditTextTest extends Activity {  /** Called when the activity is first created. */  private EditText mEdit;  @Override  public void onCreate(Bundle savedInstanceState) {  super.onCreate(savedInstanceState);  setContentView(R.layout.main);  mEdit=(LineEditText)findViewById(R.id.myEdit);  mEdit.setHint("从这里开始输入...");  mEdit.setSingleLine();  mEdit.setFilters(new InputFilter[]{new InputFilter.LengthFilter(20)});  }  }