好的，所以我尝试传递一个JSON对象，使用putExtra属性将字符串转换为另一个意图。然后下面的代码触发启动我试图添加片段的活动。但是，在尝试加载该活动时，应用程序崩溃，表示正在对空对象强制转换方法。需要帮助。
这是触发活动的代码：
detailsField[i].setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
Intent intent = new Intent(getContext() , DetailActivity.class);
intent.putExtra("jsonStr" , J.toString());
startActivity(intent);
}
});
这里是DetailActivity.java类：
public class DetailActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
//getSupportActionBar().setDisplayHomeAsUpEnabled(true);
setContentView(R.layout.activity_detail);
DetailFragment hello = new DetailFragment();
getSupportFragmentManager().beginTransaction().add(R.id.fragment_detail, hello, "HELLO").commit();
}
}
以下是片段内的方法：
public void updateView() {
try {
obj = new JSONObject(intent.getStringExtra("jsonStr"));
setWeatherIcon();
humidityIcon.setText(getActivity().getString(R.string.humidity_icon));
sunsetIcon.setText(getActivity().getString(R.string.sunset_icon));
sunriseIcon.setText(getActivity().getString(R.string.sunrise_icon));
speedIcon.setText(getActivity().getString(R.string.speed_icon));
pressureIcon.setText(getActivity().getString(R.string.pressure_icon));
Long date1 = obj.getLong("dt");
Date expiry = new Date(Long.parseLong(Long.toString(date1)) * 1000);
String date = new SimpleDateFormat("EE, dd" , Locale.US).format(expiry);
dateText.setText(date);
long dy = obj.getJSONObject("main").getLong("day");
int day = (int) dy;
sunriseText.setText("Day : " + day + getString(R.string.c));
long nt = obj.getJSONObject("main").getLong("night");
int night = (int) nt;
sunsetText.setText("Night : " + night + getString(R.string.c));
SpannableString ss1= new SpannableString(date + "\n"
+ obj.getJSONObject("temp").getLong("max") + "°" + " "
+ obj.getJSONObject("temp").getLong("min") + "°" + "\n");
ss1.setSpan(new RelativeSizeSpan(1.1f), 0,7, 0); // set size
ss1.setSpan(new RelativeSizeSpan(1.4f) , 8 , 11 , 0);
tempText.setText(ss1);
humidityText.setText(obj.getInt("humidity") + "%");
speedText.setText(obj.getLong("speed") + " km/h");
pressureText.setText(obj.getLong("pressure") + " hPa");
}
catch (JSONException ex) {
Log.e("Detail View" , "Cannot Find Details");
getActivity().finish();
}
}
private void setWeatherIcon() throws JSONException {
int id = obj.getJSONArray("weather").getJSONObject(0).getInt("id");
String icon = "";
switch(id) {
/*Many Switch Cases above which do not cause problem*/
case 900 :
case 781 : icon = getActivity().getString(R.string.weather_tornado);
break;
case 904 :
case 800 : icon = getActivity().getString(R.string.weather_sunny);
break;
case 801 :
case 802 :
/*Many Switch Cases below which do not cause problem*/
}
weatherIcon.setText(icon);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_detail, container, false);
cityField = (TextView) rootView.findViewById(R.id.city_field);
dateText = (TextView) rootView.findViewById(R.id.date_text);
weatherIcon = (TextView) rootView.findViewById(R.id.weather_icon);
weatherIcon.setTypeface(weatherFont);
tempText = (TextView) rootView.findViewById(R.id.temp_text);
humidityIcon = (TextView) rootView.findViewById(R.id.humidity_icon);
humidityIcon.setTypeface(weatherFont);
humidityText = (TextView) rootView.findViewById(R.id.humidity_text);
speedIcon = (TextView) rootView.findViewById(R.id.speed_icon);
speedIcon.setTypeface(weatherFont);
speedText = (TextView) rootView.findViewById(R.id.speed_text);
pressureIcon = (TextView) rootView.findViewById(R.id.pressure_icon);
pressureIcon.setTypeface(weatherFont);
pressureText = (TextView) rootView.findViewById(R.id.pressure_text);
sunriseIcon = (TextView) rootView.findViewById(R.id.sunrise_icon);
sunriseIcon.setTypeface(weatherFont);
sunriseText = (TextView) rootView.findViewById(R.id.sunrise_text);
sunsetIcon = (TextView) rootView.findViewById(R.id.sunset_icon);
sunsetIcon.setTypeface(weatherFont);
sunsetText = (TextView) rootView.findViewById(R.id.sunset_text);
return rootView;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
weatherFont = Typeface.createFromAsset(getActivity().getAssets(), "fonts/newweather.ttf");
intent = getActivity().getIntent();
updateView();
}
这里是activity_detail.xml文件，用于DetailActivity
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:context="com.a5corp.weather.DetailActivity">
<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="@style/AppTheme.AppBarOverlay">
<android.support.v7.widget.Toolbar
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="?attr/colorPrimary"
app:popupTheme="@style/AppTheme.PopupOverlay" />
</android.support.design.widget.AppBarLayout>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/fragment_detail"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.a5corp.weather.WeatherActivity"
tools:ignore="MergeRootFrame"
android:background="@color/colorPrimary" />
</android.support.design.widget.CoordinatorLayout>
我不知道我是否应该提供片段xml，因为我的片段定义得很好。
以下是错误消息：
12-21 23:33:23.777 13286-13286/com.a5corp.weather E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.a5corp.weather, PID: 13286
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.a5corp.weather/com.a5corp.weather.DetailActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2423)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2483)
at android.app.ActivityThread.access$900(ActivityThread.java:153)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1349)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5441)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:738)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:628)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
at com.a5corp.weather.DetailFragment.setWeatherIcon(DetailFragment.java:157)
at com.a5corp.weather.DetailFragment.updateView(DetailFragment.java:37)
at com.a5corp.weather.DetailFragment.onCreate(DetailFragment.java:196)
at android.support.v4.app.Fragment.performCreate(Fragment.java:2075)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1060)
at android.support.v4.app.BackStackRecord.setLastIn(BackStackRecord.java:838)
at android.support.v4.app.BackStackRecord.calculateFragments(BackStackRecord.java:861)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:719)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1682)
at android.support.v4.app.FragmentController.execPendingActions(FragmentController.java:388)
at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:607)
at android.support.v7.app.AppCompatActivity.onStart(AppCompatActivity.java:181)
at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1238)
at android.app.Activity.performStart(Activity.java:6320)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2386)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2483)
at android.app.ActivityThread.access$900(ActivityThread.java:153)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1349)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5441)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:738)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:628)
（片段中的第157行是setWeatherIcon（）函数中的weatherIcon.setText(icon)。
第37行是在Fragment的updateView（）中调用的setWeatherIcon（）
第96行是在Fragment＆＃39; onCreate（）中调用的updateView（））
（即使我注释掉了这行，它为另一个TextView提供了相同的NullPointerException，注释那个也为另一个TextView提供了另一个NullPointerException）
答案 0 :(得分：2)
根据片段生命周期，onCreate()是第一个被调用的方法。但是视图是在onCreateView函数中生成和初始化的。因此，在初始化onCreate函数之前，您要在UI元素中设置值。
从updateView()方法移除调用onCreate()并将其放入onCreateView函数中。
答案 1 :(得分：0)
片段与活动
的生命周期不同@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// updateView(); There is no view yet... All Views are null
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_detail, container, false);
cityField = (TextView) rootView.findViewById(R.id.city_field);
dateText = (TextView) rootView.findViewById(R.id.date_text);
...
// Now there are some views (assuming the XML is correct)
return rootView;
}
@Override
public void onViewCreated(View view, Bundle savedInstanceState) {
// Now there are definitely some views (again, same assumptions)
}
因此，在分配视图后，您必须致电updateView 。
片段使用getArguments()来获取额外内容。不确定为什么需要intent = getActivity().getIntent();
答案 2 :(得分：0)
@rahulkapoor有你崩溃的确切解决方案。
我在这里回答是为了清除从Activity到Fragment传递参数的想法。你做错了。
因此，您启动了DetailsActivity并传递了一些intent。您需要首先在onCreate的{{1}}函数中获取intent中的额外内容。
然后，在从DetailsActivity的{{1}}函数启动Fragment之前，您需要将信息作为参数传递给启动onCreate。
DetailsActivity现在，在Fragment的{{1}}函数中，您需要获取参数并相应地更新您的视图。您可以从public class DetailActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
setContentView(R.layout.activity_detail);
// Now set the arguments in your launching fragment.
DetailFragment hello = new DetailFragment();
hello.setArguments(getIntent().getExtras());
// Now launch the Fragment.
getSupportFragmentManager().beginTransaction().add(R.id.fragment_detail, hello, "HELLO").commit();
}
}
删除onCreateView功能。
Fragment