效果圖

1.MainActivity.java

 1 package com.example.app2;
 2 
 3 import android.support.v7.app.AppCompatActivity;
 4 import android.os.Bundle;
 5 import android.view.View;
 6 import android.widget.EditText;
 7 import android.widget.TextView;
 8 
 9 public class MainActivity extends AppCompatActivity {
 
10     private TextView textView;
11     private EditText editText;
12 
13     @Override
14     protected void onCreate(Bundle savedInstanceState) {
15         super.onCreate(savedInstanceState);
16         setContentView(R.layout.activity_main);
17 
18         textView = (TextView) findViewById(R.id.tv_show);
 
19         editText = (EditText) findViewById(R.id.et_mail1);
20 
21         editText.setOnFocusChangeListener(new View.OnFocusChangeListener() {
22             @Override
23             public void onFocusChange(View v, boolean hasFocus) {
24                 String et_info = editText.getText().toString();
 
25                 String reges="\\w+@\\w+(\\.\\w{2,3})*\\.\\w{2,3}";      //正則表達式驗證郵箱是否正確
26                 if(et_info.matches(reges)){
27                     textView.setText("您輸入的郵箱是："+et_info+"符合條件");
28                 }else{
29                     textView.setText("您輸入的郵箱是："+et_info+"不符合條件");
30                 }
31             }
32         });
33 
34     }
35 }

2.activity_main.xml

 1 <?xml version="1.0" encoding="utf-8"?>
 2 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 3     xmlns:tools="http://schemas.android.com/tools"
 4     android:layout_width="match_parent"
 5     android:layout_height="match_parent"
 6     android:paddingBottom="@dimen/activity_vertical_margin"
 7     android:paddingLeft="@dimen/activity_horizontal_margin"
 8     android:paddingRight="@dimen/activity_horizontal_margin"
 9     android:paddingTop="@dimen/activity_vertical_margin"
10     tools:context="com.example.app2.MainActivity"
11     android:orientation="vertical"
12     >
13 
14     <TextView
15         android:layout_width="wrap_content"
16         android:layout_height="wrap_content"
17         android:text="請輸入您的郵箱" />
18     <EditText
19         android:id="@+id/et_mail1"
20         android:hint="第一個文本輸入框"
21         android:layout_width="match_parent"
22         android:layout_height="wrap_content" />
23     <EditText
24         android:id="@+id/et_mail2"
25         android:hint="第二個文本輸入框"
26         android:layout_width="match_parent"
27         android:layout_height="wrap_content" />
28     <TextView
29         android:id="@+id/tv_show"
30         android:layout_width="wrap_content"
31         android:layout_height="wrap_content" />
32 </LinearLayout>

焦點改變事件OnFocusChangeListener