在 android 微调器上获取空指针

Question

我正在尝试将微调器实现到操作栏中，但是当我尝试设置适配器时，我得到了一个空指针引用。我不知道问题出在哪里，因为我之前在 activity 中设置它时它工作正常。

这是我的代码

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    if (!mNavigationDrawerFragment.isDrawerOpen()) {
        // Inflate the menu; this adds items to the action bar if it is present.if (!mNavigationDrawerFragment.isDrawerOpen()) {
        // Only show items in the action bar relevant to this screen
        // if the drawer is not showing. Otherwise, let the drawer
        // decide what to show in the action bar.
        getMenuInflater().inflate(R.menu.menu_game, menu);
        restoreActionBar();
        Spinner s = (Spinner) menu.findItem(R.id.menu_spinner).getActionView(); // find the spinner
        /*SpinnerAdapter mSpinnerAdapter = ArrayAdapter.createFromResource(this.getSupportActionBar()
                .getThemedContext(), R.array.mile_selections, android.R.layout.simple_spinner_dropdown_item); //  create the adapter from a StringArray*/
        ArrayAdapter<CharSequence> spinnerAdapter = ArrayAdapter.createFromResource(this, R.array.mile_selections, android.R.layout.simple_spinner_item);
        spinnerAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        s.setAdapter(spinnerAdapter); // set the adapter
        s.setOnItemSelectedListener(this);
        return true;
    }
    return super.onCreateOptionsMenu(menu);
}

这是错误

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Spinner.setAdapter(android.widget.SpinnerAdapter)' on a null object reference
        at com.sousheelvunnam.scrimmage.ui.GameActivity.onCreateOptionsMenu(GameActivity.java:138)

Answer 1

根据其他一些 Whosebug posts，您需要在调用 getActionView 之前对菜单对象调用 setActionView。

此 post 有以下评论：

Casting a Menu Item in XML to a Spinner (Actionbar appcompat)

No, but it lead me to another question with almost the same name: whosebug.com/questions/14286768/… Apperently getActionView doesnt work unless you use setActionView first. So it does not pick it up from XML – ThomQ Apr 10 '14 at 0:01

这里是 link 到 post 表示您必须使用 SetActionView。

getActionView() of my MenuItem return null

Answer 2

我遇到了同样的问题。如果您遵循上面的评论链，您会发现您不需要使用 setActionView。您只需要正确设置布局 XML：

I had the same issue and I my error was that I wasn't properly using the actionLayout xml attribute properly. First of all, you must define a custom namespace in the menu tag like this xmlns:app="http://schemas.android.com/apk/res-auto" Then on the menu item you want to have to use the actionLayout attribute like this: app:actionLayout="@layout/month_picker" In this case the month_picker layout is a spinner. Doing this makes it unnecessary to use the setActionView method. – Jorge Salas May 25 '15 at 0:50

对我有用。

在 android 微调器上获取空指针

Getting a null pointer on android spinner

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