打勾显示输入的密码 EditText与setTransformationMethod

package com.wzc.ex03_22;

import android.support.v7.app.AppCompatActivity;
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.EditText;

public class MainActivity extends AppCompatActivity {

    private EditText et;
    private CheckBox cb;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        et = (EditText) findViewById(R.id.et_01);
        cb = (CheckBox) findViewById(R.id.checkBox);
        /* 设置CheckBox的OnCheckedChangeListener */
        cb.setOnCheckedChangeListener(new CheckBox.OnCheckedChangeListener(){
            @Override
            public void onCheckedChanged(CompoundButton compoundButton, boolean b) {
                if (cb.isChecked()){
                    // 设置EditText的内容为可见的
                    et.setTransformationMethod(HideReturnsTransformationMethod.getInstance());
                } else {
                    // 设置EditText的内容为隐藏的
                    et.setTransformationMethod(PasswordTransformationMethod.getInstance());
                }
            }
        });
    }
}

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.wzc.ex03_22.MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/app_title"
        android:id="@+id/textView" />
    <EditText
        android:id="@+id/et_01"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textSize="18sp"
        android:textColor="@drawable/black"
        android:inputType="textPassword"
        android:hint="请输入密码"
        android:layout_below="@+id/textView"
        android:layout_alignParentStart="true" />

    <CheckBox
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/show_key"
        android:id="@+id/checkBox"
        android:layout_below="@+id/et_01" />

</RelativeLayout>