效果图

布局文件

<?xml version="1.0" encoding="utf-8"?>
<!-- Android中EditText显示明文与密文的两种方式 -->
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    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.why.project.androidcnblogsdemo.MainActivity">

    <!-- 输入密码区域 -->
    <EditText
        android:id="@+id/edt_password"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:background="@drawable/comm_input_selector"
        android:hint="请输入密码"
        android:textSize="18sp"
        android:imeOptions="actionGo"
        android:inputType="textPassword"
        android:text=""
        android:textColor="#999999"
        android:textColorHint="#999999"
        android:drawableLeft="@drawable/pwd_img"
        android:drawablePadding="10dp"
        android:layout_margin="5dp"
        />

    <!-- 显示隐藏密码图标 -->
    <ImageView
        android:id="@+id/img_pwdshow"
        android:layout_width="wrap_content"
        android:layout_height="50dp"
        android:src="@drawable/pwd_hidden"
        android:scaleType="fitCenter"
        android:contentDescription="控制密码明文密文显示"
        android:layout_alignRight="@id/edt_password"
        android:layout_alignTop="@id/edt_password"
        android:paddingLeft="10dp"
        android:paddingRight="10dp"
        android:focusable="true"
        android:clickable="true"/>
</RelativeLayout>

comm_input_selector文件

<?xml version="1.0" encoding="utf-8"?>
<!-- 输入框背景图 -->
<selector xmlns:android="http://schemas.android.com/apk/res/android" >
   <!--选中时效果-->
   <!-- <item android:state_focused="true"
        android:drawable="@drawable/input_box_focused" /> -->
   <!--disable效果 windows焦点在前时  注意写法-->
   <!-- <item android:state_window_focused="true" android:state_enabled="false"
        android:drawable="@drawable/input_box_focused" /> -->
   <!--默认时效果-->
   <!-- <item  android:drawable="@drawable/input_box_unfocused" /> -->

    <!-- 选中时效果 -->
    <item android:state_focused="true">

        <shape android:shape="rectangle">
            <!-- 圆角 -->
            <corners android:radius="3dp" />
            <!-- 描边 -->
            <stroke android:width="1dp" android:color="#1296db" />
            <!-- 内边距 -->
            <padding
                android:bottom="5dp"
                android:left="5dp"
                android:right="5dp"
                android:top="5dp" />
            <!-- 填充 -->
            <solid android:color="@android:color/transparent" />
        </shape>
    </item>
    <!-- disable效果 windows焦点在前时  注意写法 -->
    <item android:state_enabled="false" android:state_window_focused="true">

        <shape android:shape="rectangle">
            <!-- 圆角 -->
            <corners android:radius="3dp" />
            <!-- 描边 -->
            <stroke android:width="1dp" android:color="#1296db" />
            <!-- 内边距 -->
            <padding
                android:bottom="5dp"
                android:left="5dp"
                android:right="5dp"
                android:top="5dp" />
            <!-- 填充 -->
            <solid android:color="@android:color/transparent" />
        </shape>

    </item>
    <!-- 默认时效果 -->
    <item>
        <shape android:shape="rectangle">
            <!-- 圆角 -->
            <corners android:radius="3dp" />
            <!-- 描边 -->
            <stroke android:width="1dp" android:color="#9f9f9f" />
            <!-- 内边距 -->
            <padding
                android:bottom="5dp"
                android:left="5dp"
                android:right="5dp"
                android:top="5dp" />
            <!-- 填充 -->
            <solid android:color="@android:color/transparent" />
        </shape>
    </item>

</selector>

comm_input_selector

方式一

/**方式一：*/
    private void showOrHiddenPwd(){
        if(! showPwd){
            showPwd = true;
            img_pwdshow.setImageResource(R.drawable.pwd_show);
            //显示密码
            edt_password.setTransformationMethod(HideReturnsTransformationMethod.getInstance());
        }else{
            showPwd = false;
            img_pwdshow.setImageResource(R.drawable.pwd_hidden);
            //隐藏密码
            edt_password.setTransformationMethod(PasswordTransformationMethod.getInstance());
        }
    }

方式二

/**方式二：*/
    private void showOrHiddenPwdWithInputType(){
        if(! showPwd){
            showPwd = true;
            img_pwdshow.setImageResource(R.drawable.pwd_show);
            //显示密码
            edt_password.setInputType(InputType.TYPE_TEXT_VARIATION_VISIBLE_PASSWORD);
        }else{
            showPwd = false;
            img_pwdshow.setImageResource(R.drawable.pwd_hidden);
            //隐藏密码
            edt_password.setInputType(InputType.TYPE_CLASS_TEXT | InputType.TYPE_TEXT_VARIATION_PASSWORD);
        }
    }

使用方式

package com.why.project.androidcnblogsdemo;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.text.InputType;
import android.text.method.HideReturnsTransformationMethod;
import android.text.method.PasswordTransformationMethod;
import android.view.View;
import android.widget.EditText;
import android.widget.ImageView;

/**
 * Android中EditText显示明文与密文的两种方式*/
public class MainActivity extends AppCompatActivity {

    private EditText edt_password;
    private ImageView img_pwdshow;
    private boolean showPwd = false;//默认不显示密码

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        initViews();
        initEvents();
    }

    private void initViews() {
        edt_password = (EditText) findViewById(R.id.edt_password);
        img_pwdshow = (ImageView) findViewById(R.id.img_pwdshow);
    }

    private void initEvents() {
        img_pwdshow.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                showOrHiddenPwdWithInputType();
            }
        });
    }

    /**方式一：*/
    private void showOrHiddenPwd(){
        if(! showPwd){
            showPwd = true;
            img_pwdshow.setImageResource(R.drawable.pwd_show);
            //显示密码
            edt_password.setTransformationMethod(HideReturnsTransformationMethod.getInstance());
        }else{
            showPwd = false;
            img_pwdshow.setImageResource(R.drawable.pwd_hidden);
            //隐藏密码
            edt_password.setTransformationMethod(PasswordTransformationMethod.getInstance());
        }
    }

    /**方式二：*/
    private void showOrHiddenPwdWithInputType(){
        if(! showPwd){
            showPwd = true;
            img_pwdshow.setImageResource(R.drawable.pwd_show);
            //显示密码
            edt_password.setInputType(InputType.TYPE_TEXT_VARIATION_VISIBLE_PASSWORD);
        }else{
            showPwd = false;
            img_pwdshow.setImageResource(R.drawable.pwd_hidden);
            //隐藏密码
            edt_password.setInputType(InputType.TYPE_CLASS_TEXT | InputType.TYPE_TEXT_VARIATION_PASSWORD);
        }
    }
}

参考资料

Android基础--登陆界面，密码的隐藏和显示

Android中EditText显示明文与密码的两种方式