Android:如何在按钮单击时启用/禁用选项菜单项？

Question

当我使用 onCreateOptionsMenu 或 onOptionsItemSelected 方法时，我可以轻松做到这一点。

但我在屏幕某处有一个按钮，单击该按钮时，它应该启用/禁用上下文菜单项。

Answer 1

无论如何，the documentation涵盖所有内容。

在运行时更改菜单项

Once the activity is created, the onCreateOptionsMenu() method is called only once, as described above. The system keeps and re-uses the Menu you define in this method until your activity is destroyed. If you want to change the Options Menu any time after it's first created, you must override the onPrepareOptionsMenu() method. This passes you the Menu object as it currently exists. This is useful if you'd like to remove, add, disable, or enable menu items depending on the current state of your application.

例如

@Override
public boolean onPrepareOptionsMenu (Menu menu) {
    if (isFinalized) {
        menu.getItem(1).setEnabled(false);
        // You can also use something like:
        // menu.findItem(R.id.example_foobar).setEnabled(false);
    }
    return true;
}

在 Android 3.0 及更高版本上，当菜单项出现在操作栏中时，选项菜单被视为始终处于打开状态。当事件发生时，你要进行菜单更新，你必须调用invalidateOptionsMenu()来请求系统调用onPrepareOptionsMenu()。