Java Android上的简单微调器出错
我正在学习Android中的微调器,并测试了Android开发者链接中出现的代码: 但它不起作用,这些是文件: MainActivity.javaJava Android上的简单微调器出错,java,android,spinner,android-spinner,Java,Android,Spinner,Android Spinner,我正在学习Android中的微调器,并测试了Android开发者链接中出现的代码: 但它不起作用,这些是文件: MainActivity.java ... protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); Spinner spinner = (Spinner) f
...
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Spinner spinner = (Spinner) findViewById(R.id.planets_spinner);
// Create an ArrayAdapter using the string array and a default spinner layout
ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(this,
R.array.planets_array, android.R.layout.simple_spinner_item);
// Specify the layout to use when the list of choices appears
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
// Apply the adapter to the spinner
spinner.setAdapter(adapter);
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment())
.commit();
}
}
...
第28行是:
spinner.setAdapter(adapter);
你能解释一下为什么它现在能用吗?谢谢大家! 您当前正在加载布局活动\u main.xml:
setContentView(R.layout.activity_main);
但是微调器是在名为fragment_main.xml的布局中定义的
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.spinners.MainActivity$PlaceholderFragment" >
<Spinner
android:id="@+id/planets_spinner"
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
改变
setContentView(R.layout.activity_main);
与
编辑:
根据评论,问题似乎是您在尝试从活动访问xml布局中的元素之前没有加载片段。谢谢您的回答@maraci,这是解决方案: 填充微调器的代码必须放在片段类的onCreateView方法中,因此MainActivity.java如下所示:
public class MainActivity extends ActionBarActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment())
.commit();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
Spinner spinner = (Spinner) rootView.findViewById(R.id.planets_spinner);
ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(getActivity(),R.array.planets_array, android.R.layout.simple_spinner_item);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinner.setAdapter(adapter);
return rootView;
}
}
}
公共类MainActivity扩展了ActionBarActivity{
@凌驾
创建时受保护的void(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
如果(savedInstanceState==null){
getSupportFragmentManager().beginTransaction()
.add(R.id.container,新的占位符片段())
.commit();
}
}
@凌驾
公共布尔onCreateOptions菜单(菜单){
getMenuInflater().充气(R.menu.main,menu);
返回true;
}
@凌驾
公共布尔值onOptionsItemSelected(菜单项项){
int id=item.getItemId();
if(id==R.id.action\u设置){
返回true;
}
返回super.onOptionsItemSelected(项目);
}
/**
*包含简单视图的占位符片段。
*/
公共静态类占位符片段扩展了片段{
公共占位符片段(){
}
@凌驾
创建视图上的公共视图(布局、充气机、视图组容器、,
Bundle savedInstanceState){
视图根视图=充气机。充气(R.layout.fragment_main,容器,错误);
微调器微调器=(微调器)rootView.findViewById(R.id.planets\u微调器);
ArrayAdapter=ArrayAdapter.createFromResource(getActivity(),R.array.planets\u数组,android.R.layout.simple\u微调器\u项);
setDropDownViewResource(android.R.layout.simple\u微调器\u下拉菜单\u项);
旋转器。设置适配器(适配器);
返回rootView;
}
}
}
谢谢,但是MainActivity.java中还有其他方法管理布局“activity\u main”和“fragment\u main”,如果我在注释中输入填充微调器的代码,它会工作,但微调器为空,因此,错误是填充微调器。抱歉,我想我只是不确定您当前的活动/片段设置是什么。根据您问题中的信息,我认为问题在于findViewById(R.id.plants\u微调器)返回null。对我来说,这似乎是因为从未加载包含xml微调器的视图,而您的活动对此一无所知。你说“如果我在注释中添加填充微调器的代码有效”是什么意思?注释代码?此外,您可能会在活动生命周期的稍后时间加载片段代码。如果是这样的话,那么在尝试查找微调器时得到null返回是有意义的,因为片段尚未加载。请确保先加载片段,然后在微调器上使用findViewById。您好,我的internet连接已断开。。。你是对的,微调器是空的,因为我试图在创建它之前使用它。我会把代码放在哪里,不用担心。很高兴你能找到问题!你让它工作了吗???
setContentView(R.layout.activity_main);
setContentView(R.layout.activity_main);
setContentView(R.layout.fragment_main);
public class MainActivity extends ActionBarActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment())
.commit();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
Spinner spinner = (Spinner) rootView.findViewById(R.id.planets_spinner);
ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(getActivity(),R.array.planets_array, android.R.layout.simple_spinner_item);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinner.setAdapter(adapter);
return rootView;
}
}
}