<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:orientation="vertical" >
 <EditText
  android:id="@+id/editText1"
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:ems="10"
  android:inputType="textPassword" >
  <requestFocus />
 </EditText>
 <CheckBox
  android:id="@+id/checkBox1"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:text="顯示密碼" />
</LinearLayout>

package com.example.test;
import android.app.Activity;
import android.os.Bundle;
import android.text.method.HideReturnsTransformationMethod;
import android.text.method.PasswordTransformationMethod;
import android.widget.CheckBox;
import android.widget.CompoundButton;
import android.widget.CompoundButton.OnCheckedChangeListener;
import android.widget.TextView;
public class MainActivity extends Activity {
private TextView editText1;
private CheckBox checkBox1;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.test);
  editText1 =(TextView) findViewById(R.id.editText1);
  checkBox1=(CheckBox) findViewById(R.id.checkBox1);
  checkBox1.setOnCheckedChangeListener(new OnCheckedChangeListener() {
   @Override
   public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
    // TODO Auto-generated method stub
    if(isChecked){
     //如果選中，顯示密碼  
     editText1.setTransformationMethod(HideReturnsTransformationMethod.getInstance());
    }else{
     //否則隱藏密碼
     editText1.setTransformationMethod(PasswordTransformationMethod.getInstance());
    }
   }
  });
 }
}

editText1.setTransformationMethod(HideReturnsTransformationMethod.getInstance());
editText1.setTransformationMethod(PasswordTransformationMethod.getInstance());