java - FindItem(R.id.*) 抛出 NullPointerException

Question

我想为我的菜单项添加onMenuItemClickListener。问题是，当我尝试在 onCreateOptionsMenu() 之外访问 menu.findItem(R.id.*) 时，我总是收到 NullPointerException。由于某种原因，菜单项仍然无法用于任何其他功能，我不知道为什么......

    public Menu items_type;


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.items_type, menu);
        items_type=menu;
        return true;
    }

    public boolean onPrepareOptionsMenu(Menu menu) {
        items_type.clear();
        MenuItem.OnMenuItemClickListener common = new MenuItem.OnMenuItemClickListener() {
            @Override
            public boolean onMenuItemClick(MenuItem menuItem) {
                if(items_type.findItem(R.id.filename).isChecked() && menuItem.getItemId()==R.id.tracktitle)
                {
                    items_type.findItem(R.id.tracktitle).setChecked(true);
                    items_type.findItem(R.id.filename).setChecked(false);
                }
                else if(items_type.findItem(R.id.tracktitle).isChecked() && menuItem.getItemId()==R.id.filename)
                {
                    items_type.findItem(R.id.filename).setChecked(true);
                    items_type.findItem(R.id.tracktitle).setChecked(false);
                }
                return true;
            }
        };
        items_type.findItem(R.id.tracktitle).setOnMenuItemClickListener(common);
        items_type.findItem(R.id.filename).setOnMenuItemClickListener(common);
        return true;
    }

public void onCreate(Bundle savedInstanceState) {
...
}

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

    <group android:id="@id/group"
        android:checkableBehavior="single">
    <item
    android:id="@id/filename"
android:title=" File Names"
app:showAsAction="never"/>
<item
android:id="@id/tracktitle"
android:title="ID3 Titles"
app:showAsAction="never"/>

    </group>
    </menu>

Answer 1

像这样处理菜单点击事件更好 @覆盖 公共(public)无效onCreateOptionsMenu(菜单菜单，MenuInflater inflater){ super.onCreateOptionsMenu(菜单，充气器); getMenuInflater().inflate(R.menu.items_type, 菜单); }

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    int i = item.getItemId();
    if (i == android.R.id.home) {
    } else if (i == R.id.action_share_pdf) {
    }
    return super.onOptionsItemSelected(item);
}