Udacity- Android的第一课，列表视图显示不出来 [英] Udacity- Android First Lesson, Listview doesn't show up
本文介绍了Udacity- Android的第一课，列表视图显示不出来的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我检查了几次，从Udacity的视频，并试图做同样的事情，但列表视图显示不出来。能否请你检查我的code和告诉我，如果我错过了什么？
MainActivity.java
公共类MainActivity扩展ActionBarActivity { @覆盖
保护无效的onCreate（捆绑savedInstanceState）{
super.onCreate（savedInstanceState）;
的setContentView（R.layout.activity_main）;
如果（savedInstanceState == NULL）{
getSupportFragmentManager（）调用BeginTransaction（）
。新增（R.id.container，新PlaceholderFragment（））
。承诺（）;
}
}
@覆盖
公共布尔onCreateOptionsMenu（菜单菜单）{
//充气菜单;如果是present这增加了项目操作栏。
。getMenuInflater（）膨胀（R.menu.main，菜单）;
返回true;
} @覆盖
公共布尔onOptionsItemSelected（菜单项项）{
//处理动作栏项目点击这里。操作栏会
//自动处理上点击主页/向上按钮，只要
//你在AndroidManifest.xml中指定一个父活动。
INT ID = item.getItemId（）;
如果（ID == R.id.action_settings）{
返回true;
}
返回super.onOptionsItemSelected（项目）;
} / **
*包含一个简单视图中的占位符片段。
* /
公共静态类PlaceholderFragment扩展片段{ 公共PlaceholderFragment（）{
} @覆盖
公共查看onCreateView（LayoutInflater充气器，容器的ViewGroup，
捆绑savedInstanceState）{
查看rootView = inflater.inflate（R.layout.fragment_main，集装箱，FALSE）; /*//我的方式
ArrayList的＆LT;串GT; fakeData =新的ArrayList＆LT;串GT;（）;
fakeData.add（今日恒业50/60）;
fakeData.add（明天，多云20/30）;
fakeData.add（星期三，雪40/50）;
fakeData.add（周四至多雨20/40）; * / //谷歌的方式
的String [] = forecastArray {
今天，阳光50/60
明天，多云20/30
周三，雪40/50
周四多雨20/40
周五滑稽20/50
周六，阳光70/80
太阳阳光90/100
}; ArrayList的＆LT;串GT; weekForecast =新的ArrayList＆LT;串GT;（）;
Arrays.asList（weekForecast）; ArrayAdapter适配器=新ArrayAdapter＆LT;串GT;
（getActivity（），R.layout.list_item_forecast，R.id.list_item_forecast_textview，weekForecast）; ListView控件列表视图=（ListView控件）rootView.findViewById（R.id.listview_forecast）; listview.setAdapter（适配器）; 返回rootView;
}
}
}
activity_main.xml中
＆LT;的FrameLayout的xmlns：机器人=http://schemas.android.com/apk/res/android
的xmlns：工具=http://schemas.android.com/tools
机器人：ID =@ + ID /容器
机器人：layout_width =match_parent
机器人：layout_height =match_parent
工具：上下文=。MainActivity
工具：忽略=MergeRootFrame/＆GT;
fragment_main.xml
＆LT;的FrameLayout的xmlns：机器人=http://schemas.android.com/apk/res/android
的xmlns：工具=http://schemas.android.com/tools
机器人：layout_width =match_parent
机器人：layout_height =match_parent
机器人：paddingLeft =@扪/ activity_horizontal_margin
机器人：paddingRight =@扪/ activity_horizontal_margin
机器人：paddingTop =@扪/ activity_vertical_margin
机器人：paddingBottom会=@扪/ activity_vertical_margin
工具：上下文=$ MainActivity PlaceholderFragment。＆GT; ＆LT; ListView控件
机器人：layout_width =match_parent
机器人：layout_height =match_parent
机器人：ID =@ + ID / listview_forecast/＆GT;
＆LT; /＆的FrameLayout GT;
list_item_forecast.xml
＆LT; TextView中的xmlns：机器人=http://schemas.android.com/apk/res/android
机器人：layout_width =match_parent
机器人：layout_height =WRAP_CONTENT
安卓了minHeight =机器人：ATTR /列表preferredItemHeight
机器人：重力=center_vertical
机器人：ID =@ + ID / list_item_forecast_textview＆GT;
＆LT; / TextView的＆GT;
解决方案
的问题是，weekForecast已宣告但尚未初始化。替换：
的ArrayList＆LT;串GT; weekForecast =新的ArrayList＆LT;串GT;（）;
Arrays.asList（weekForecast）;
与
的ArrayList＆LT;串GT; weekForecast =新的ArrayList＆LT;串GT;（Arrays.asList（forecastArray））;
I checked several times from Udacity videos and tried to do the exact same thing but listview doesn't show up. Could you please examine my code and tell me if I miss something?
MainActivity.java
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) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, 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.
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);
/*//My way
ArrayList<String> fakeData = new ArrayList<String>();
fakeData.add("Today-Sunny 50/60");
fakeData.add("Tomorrow-Cloudy 20/30");
fakeData.add("Wednesday-Snowy 40/50");
fakeData.add("Thursday-Rainy 20/40"); */
//Google's way
String[] forecastArray={
"Today-Sunny 50/60",
"Tomorrow-Cloudy 20/30",
"Wednesday-Snowy 40/50",
"Thursday-Rainy 20/40",
"Friday-Funny 20/50",
"Sat-Sunny 70/80",
"Sun-Sunny 90/100"
};
ArrayList<String> weekForecast=new ArrayList<String>();
Arrays.asList(weekForecast);
ArrayAdapter adapter = new ArrayAdapter<String>
(getActivity(), R.layout.list_item_forecast, R.id.list_item_forecast_textview, weekForecast);
ListView listview = (ListView) rootView.findViewById(R.id.listview_forecast);
listview.setAdapter(adapter);
return rootView;
}
}
}
activity_main.xml
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity"
tools:ignore="MergeRootFrame"/>
fragment_main.xml
<FrameLayout 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:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context=".MainActivity$PlaceholderFragment">
<ListView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/listview_forecast" />
</FrameLayout>
list_item_forecast.xml
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:minHeight="?android:attr/listPreferredItemHeight"
android:gravity="center_vertical"
android:id="@+id/list_item_forecast_textview">
</TextView>
解决方案
The problem is that weekForecast has been declared but not initialized. Replace:
ArrayList<String> weekForecast=new ArrayList<String>();
Arrays.asList(weekForecast);
with:
ArrayList<String> weekForecast = new ArrayList<String>(Arrays.asList(forecastArray));
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