菜单与视图

当应用需要的显示额外的选项，但这些选项有不直接出现在主用户界面中时，菜单是非常有用的，在Android中有两种主要的菜单类型：（1）选项菜单，这种菜单显示与当前的Activity相关的信息，在Android中通过单击Menu激活选项菜单（2）上下文菜单，这种菜单显示Activity中的特定视图相关的信息，在Android中通过长按上下文菜单来激活

1、创建辅助方法

public class MainActivity extends AppCompatActivity {

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

private void createMenu(Menu menu) {
MenuItem mnu1 = menu.add(0, 0, 0, "Item 1");
{
mnu1.setAlphabeticShortcut('a');
}
MenuItem mnu2 = menu.add(0, 1, 1, "Item 2");
{
mnu2.setAlphabeticShortcut('b');
}
MenuItem mnu3 = menu.add(0, 2, 2, "Item 3");
{
mnu3.setAlphabeticShortcut('c');
}
MenuItem mnu4 = menu.add(0, 3, 3, "Item 4");
{
mnu4.setAlphabeticShortcut('d');
}
menu.add(0, 4, 4, "Item 5");
menu.add(0, 5, 5, "Item 6");
menu.add(0, 6, 6, "Item 7");
}

private boolean menuChoice(MenuItem item) {
switch (item.getItemId()) {
case 0:
Toast.makeText(this, "You clicked on Item 1",
Toast.LENGTH_LONG).show();
return true;
case 1:
Toast.makeText(this, "You clicked on Item 2",
Toast.LENGTH_LONG).show();
return true;
case 2:
Toast.makeText(this, "You clicked on Item 3",
Toast.LENGTH_LONG).show();
return true;
case 3:
Toast.makeText(this, "You clicked on Item 4",
Toast.LENGTH_LONG).show();
return true;
case 4:
Toast.makeText(this, "You clicked on Item 5",
Toast.LENGTH_LONG).show();
return true;
case 5:
Toast.makeText(this, "You clicked on Item 6",
Toast.LENGTH_LONG).show();
return true;
case 6:
Toast.makeText(this, "You clicked on Item 7",
Toast.LENGTH_LONG).show();
return true;
}
return false;
}
}
2、显示选项菜单

public class MainActivity extends AppCompatActivity {

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

WebView wv = (WebView) findViewById(R.id.webview);

WebSettings webSettings = wv.getSettings();
webSettings.setBuiltInZoomControls(true);
wv.loadUrl(
"http://chart.apis.google.com/chart" +
"?chs=300x225" +
"&cht=v" +
"&chco=FF6342,ADDE63,63C6DE" +
"&chd=t:100,80,60,30,30,30,10" +
"&chdl=A|B|C");
}
}

3、显示上下文菜单

@Override

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.jfdimarzio.webview.MainActivity"
tools:layout_editor_absoluteX="0dp"
tools:layout_editor_absoluteY="81dp">

<WebView
android:layout_width="384dp"
android:layout_height="511dp"
tools:layout_editor_absoluteX="0dp"
tools:layout_editor_absoluteY="0dp"
app:layout_constraintLeft_toLeftOf="@+id/activity_main"
tools:layout_constraintLeft_creator="0"
app:layout_constraintTop_toTopOf="@+id/activity_main"
tools:layout_constraintTop_creator="0"
app:layout_constraintRight_toRightOf="@+id/activity_main"
tools:layout_constraintRight_creator="0"
app:layout_constraintBottom_toBottomOf="@+id/activity_main"
tools:layout_constraintBottom_creator="0"
android:id="@+id/webview" />

</android.support.constraint.ConstraintLayout>