<?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/et"
    android:layout_width="match_parent"
    android:layout_height="50dp"
    android:layout_marginTop="25dp"
    android:hint="請輸入數據"
    />

  <LinearLayout
    android:layout_width="match_parent"
    android:layout_height="50dp"
    android:orientation="horizontal">

    <Button
      android:id="@+id/password"
      android:layout_width="0dp"
      android:layout_height="match_parent"
      android:layout_weight="1"
      android:text="密文"/>

    <Button
      android:id="@+id/show_text"
      android:layout_width="0dp"
      android:layout_height="match_parent"
      android:layout_marginLeft="20dp"
      android:layout_weight="1"
      android:text="明文"/>
  </LinearLayout>

  <Button
    android:id="@+id/clean"
    android:layout_width="match_parent"
    android:layout_height="50dp"
    android:text="清除"/>
</LinearLayout>

package com.chen;


import android.app.Activity;
import android.os.Bundle;
import android.text.method.HideReturnsTransformationMethod;
import android.text.method.PasswordTransformationMethod;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class MainActivity extends Activity {

  Button psd;
  Button show_text;
  EditText et;
  Button clean;

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

    //將輸入框中的內容變為密碼格式
    psd = (Button) findViewById(R.id.password);
    //將密碼變為明文
    show_text = (Button) findViewById(R.id.show_text);
    //清空輸入框
    clean = (Button) findViewById(R.id.clean);
    et = (EditText) findViewById(R.id.et);
    show_text.setOnClickListener(new View.OnClickListener() {
      @Override
      public void onClick(View v) {
        //獲取編輯框中的數據內容
        String context = et.getText().toString();
        //將密碼變為明文，這里不用setInputType
        et.setTransformationMethod(HideReturnsTransformationMethod.getInstance());
        //設置光標位置在數據最后
        et.setSelection(context.length());
      }
    });
    psd.setOnClickListener(new View.OnClickListener() {
      @Override
      public void onClick(View v) {
        //獲取編輯框中的數據內容
        String context = et.getText().toString();
        //將數據變為指定樣式的密碼
        et.setTransformationMethod(new AsteriskPasswordTransformationMethod());
        //設置光標位置在數據最后
        et.setSelection(context.length());
      }
    });
    clean.setOnClickListener(new View.OnClickListener() {
      @Override
      public void onClick(View v) {
        et.setText("");
      }
    });

  }

  private class AsteriskPasswordTransformationMethod extends PasswordTransformationMethod {
    @Override
    public CharSequence getTransformation(CharSequence source, View view) {
      return new PasswordCharSequence(source);
    }

    private class PasswordCharSequence implements CharSequence {
      private CharSequence mSource;

      public PasswordCharSequence(CharSequence source) {
        mSource = source; // Store char sequence
      }

      public char charAt(int index) {
        /*
        當在編輯框中輸入1的時候，會連續打印0...
        當在編輯框中繼續輸入2的時候，會連續01...
        不影響功能使用，但是出現原因不知，待解決
         */
        System.out.println("-----" + index + "-----");
        //這里返回的char，就是密碼的樣式，注意，是char類型的
        return '$'; // This is the important part
      }

      public int length() {
        return mSource.length(); // Return default
      }

      public CharSequence subSequence(int start, int end) {
        return mSource.subSequence(start, end); // Return default
      }
    }
  }

}