public class MainActivity extends AppCompatActivity {  //定義 “字體大小” 菜單項的標識  final int FONT_10 = 0x111;  final int FONT_12 = 0x112;  final int FONT_14 = 0x113;  final int FONT_16 = 0x114;  final int FONT_18 = 0x115;  //定義“普通菜單項” 的標識  final int PLAIN_ITEM = 0x11b;  //定義“字體顏色”的菜單項的標識  final int FONT_RED = 0x116;  final int FONT_BLUE = 0x117;  final int FONT_GREEN = 0x118;  private EditText editText;  @Override  protected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    editText = (EditText) findViewById(R.id.txt);  }  //當用戶點擊按鈕鍵時 觸發該方法  @Override  public boolean onCreateOptionsMenu(Menu menu) {    //添加字體大小的子菜單    SubMenu fontMenu = menu.addSubMenu("字體大小");    //設置菜單圖標    fontMenu.setIcon(R.drawable.seek02);    //設置菜單頭的圖標    fontMenu.setHeaderIcon(R.drawable.seek03);    //設置菜單頭的標題    fontMenu.setHeaderTitle("選擇字體大小");    fontMenu.add(0, FONT_10, 0 ,"10號字體");    fontMenu.add(0, FONT_12, 0 ,"12號字體");    fontMenu.add(0, FONT_14, 0 ,"14號字體");    fontMenu.add(0, FONT_16, 0 ,"16號字體");    fontMenu.add(0, FONT_18, 0 ,"18號字體");    //向Menu中添加普通菜單項    menu.add(0, PLAIN_ITEM, 0, "普通菜單選項");    //向Menu中添加"字體顏色"的子菜單    SubMenu colorMenu = menu.addSubMenu("字體顏色");    colorMenu.setIcon(R.drawable.find1);    //設置菜單頭圖標    colorMenu.setHeaderIcon(R.drawable.find);    //設置菜單頭標題    colorMenu.setHeaderTitle("選擇文字顏色");    colorMenu.add(0, FONT_RED, 0, "紅色");    colorMenu.add(0, FONT_GREEN, 0, "綠色");    colorMenu.add(0, FONT_BLUE, 0, "藍色");    return super.onCreateOptionsMenu(menu);  }  @Override  public boolean onOptionsItemSelected(MenuItem item) {    //判斷單機的是那個菜單項    switch (item.getItemId()){      case FONT_10:        editText.setTextSize(10*2);        break;      case FONT_12:        editText.setTextSize(12*2);        break;      case FONT_14:        editText.setTextSize(14*2);        break;      case FONT_16:        editText.setTextSize(16*2);        break;      case FONT_18:        editText.setTextSize(18*2);        break;      case FONT_RED:        editText.setTextColor(Color.RED);        break;      case FONT_GREEN:        editText.setTextColor(Color.GREEN);        break;      case FONT_BLUE:        editText.setTextColor(Color.BLUE);        break;      case PLAIN_ITEM:        Toast.makeText(MainActivity.this,"you click menu",Toast.LENGTH_SHORT).show();        break;    }    return true;  }}

<?xml version="1.0" encoding="utf-8"?><android.support.constraint.ConstraintLayout  xmlns:android="http://schemas.android.com/apk/res/android"  xmlns:tools="http://schemas.android.com/tools"  xmlns:app="http://schemas.android.com/apk/res-auto"  android:layout_width="match_parent"  android:layout_height="match_parent"  tools:context=".MainActivity">  <EditText    android:id="@+id/txt"    android:layout_width="match_parent"    android:layout_height="wrap_content"    android:hint="用于測試的內容"/></android.support.constraint.ConstraintLayout>