java - 创建按钮下拉菜单

Question

如何制作如下图所示的下拉菜单？

我的应用程序中有一个 + 按钮。单击时，我希望它在 + button 下显示下拉菜单。

这是我到目前为止所尝试过的。单击 + 按钮 时，不会显示下拉菜单。

MainActivity.java

public class MainActivity extends AppCompatActivity {

    Button addNew; // for + button

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

        addNew=(Button)findViewById(R.id.add);
        addNew.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                PopupMenu po=new PopupMenu(MainActivity.this,addNew); //for drop-down menu
                po.getMenuInflater().inflate(R.menu.popup_menu,po.getMenu());

                po.setOnMenuItemClickListener(new PopupMenu.OnMenuItemClickListener()
                {
                    public boolean onMenuItemClick(MenuItem item)
                    {
                       return true;
                    }
                });
            }
        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
       MenuInflater inflater=getMenuInflater();
       inflater.inflate(R.menu.create_menu,menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
       switch(item.getItemId()){
           case R.id.add:
       }
        return super.onOptionsItemSelected(item);
    }
}

popup_menu.xml

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">

    <item
        android:id="@+id/addForm"
        android:title="Create New "/>

    <item
        android:id="@+id/editForm"
        android:title="Edit File"/>


</menu>

有人可以给我提示吗？谢谢

Answer 1

您尚未将 PopMenu 的可见性设置为可见

使用

   po.show();