这是我片段的xml：
<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"
tools:context="com.thenewjonathan.foodtracker.fragments.FoodItemDisplay"
>
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textSize="50dp"
android:textStyle="bold"
android:text="blank"
android:id="@+id/foodItemNameView"
android:gravity="center"
android:layout_gravity="top|left|center"
android:textAlignment="center"/>
<ImageView
android:contentDescription="@string/foodPicture"
android:layout_width="241dp"
android:layout_height="241dp"
android:layout_gravity="left|center_vertical"
android:background="@color/material_blue_grey_800"
android:layout_below="@id/foodItemNameView"
android:id="@+id/foodPic"
/>
<RelativeLayout
android:layout_width="140dp"
android:layout_height="241dp"
android:layout_alignParentRight="true"
android:layout_below="@id/foodItemNameView"
android:layout_gravity="end|center_vertical"
android:gravity="center"
android:id="@+id/checkBoxGroup"
>
<CheckBox
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Monday"
android:id="@+id/mondayBox"
android:layout_alignParentTop="true"
android:layout_alignParentStart="true"/>
<CheckBox
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Tuesday"
android:id="@+id/tuesdayBox"
android:layout_below="@id/mondayBox"
android:layout_alignParentStart="true"/>
<CheckBox
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Wednesday"
android:id="@+id/wednesdayBox"
android:layout_below="@id/tuesdayBox"
android:layout_alignParentStart="true"/>
<CheckBox
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Thursday"
android:id="@+id/thursdayBox"
android:layout_below="@id/wednesdayBox"
android:layout_alignParentStart="true"/>
<CheckBox
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Friday"
android:id="@+id/fridayBox"
android:layout_below="@id/thursdayBox"
android:layout_alignParentStart="true"/>
<CheckBox
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Saturday"
android:id="@+id/saturdayBox"
android:layout_below="@id/fridayBox"
android:layout_alignParentStart="true"/>
<CheckBox
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Sunday"
android:id="@+id/sundayBox"
android:layout_below="@id/saturdayBox"
android:layout_alignParentStart="true"/>
</RelativeLayout>
这是片段的java文件:( FoodItem只是一个自定义对象，用于存储片段代表的每个食物项目的信息）
package com.thenewjonathan.foodtracker.fragments;
import android.app.Activity;
import android.app.Fragment;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.CheckBox;
import android.widget.ImageView;
import android.widget.TextView;
import com.thenewjonathan.foodtracker.R;
import com.thenewjonathan.foodtracker.enums.GoodBad;
import com.thenewjonathan.foodtracker.objects.FoodItem;
public class FoodItemDisplay extends Fragment
{
private static final String FOOD_ITEM_NAME = "blank";
private FoodItem foodItem;
private String foodItemName;
private ImageView image;
private TextView itemNameView;
private CheckBox mondayBox;
private CheckBox tuesdayBox;
private CheckBox wednesdayBox;
private CheckBox thursdayBox;
private CheckBox fridayBox;
private CheckBox saturdayBox;
private CheckBox sundayBox;
public FoodItemDisplay()
{
setFoodItem(new FoodItem("blank", GoodBad.HEALTHY, "blank"));
}
public static FoodItemDisplay newInstance(String inFoodItemName)
{
FoodItemDisplay fragment = new FoodItemDisplay();
Bundle args = new Bundle();
args.putString(FOOD_ITEM_NAME, inFoodItemName);
fragment.setArguments(args);
return fragment;
}
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
if (getArguments() != null)
{
foodItemName = getArguments().getString(FOOD_ITEM_NAME);
}
itemNameView = (TextView) itemNameView.findViewById(R.id.foodItemNameView);
image = (ImageView) image.findViewById(R.id.foodPic);
mondayBox = (CheckBox) mondayBox.findViewById(R.id.mondayBox);
tuesdayBox = (CheckBox) tuesdayBox.findViewById(R.id.tuesdayBox);
wednesdayBox = (CheckBox) wednesdayBox.findViewById(R.id.wednesdayBox);
thursdayBox = (CheckBox) thursdayBox.findViewById(R.id.thursdayBox);
fridayBox = (CheckBox) fridayBox.findViewById(R.id.fridayBox);
saturdayBox = (CheckBox) saturdayBox.findViewById(R.id.saturdayBox);
sundayBox = (CheckBox) sundayBox.findViewById(R.id.sundayBox);
if (foodItem != null)
{
setValues();
}
}
public void setValues()
{
if(itemNameView == null)
{
return;
}
itemNameView.setText(foodItem.getName());
image.setImageResource(image.getResources()
.getIdentifier(foodItem.getImgName(), "drawable", this.getClass().getPackage().toString()));
mondayBox.setChecked(foodItem.isMonday());
tuesdayBox.setChecked(foodItem.isTuesday());
wednesdayBox.setChecked(foodItem.isWednesday());
thursdayBox.setChecked(foodItem.isThursday());
fridayBox.setChecked(foodItem.isFriday());
saturdayBox.setChecked(foodItem.isSaturday());
sundayBox.setChecked(foodItem.isSunday());
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
return inflater.inflate(R.layout.food_item_display, container, false);
}
@Override
public void onAttach(Activity activity)
{
super.onAttach(activity);
}
@Override
public void onDetach()
{
super.onDetach();
}
public FoodItem getFoodItem()
{
return foodItem;
}
public void setFoodItem(FoodItem foodItem)
{
this.foodItem = foodItem;
}
public String getFoodItemName()
{
return foodItemName;
}
public void setFoodItemName(String foodItemName)
{
this.foodItemName = foodItemName;
}
}
以下是我将片段放在以下的课程：
public class HealthyFoods extends Activity
{
private ArrayList<FoodItem> foodItemList;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.healthy_foods);
foodItemList = new ArrayList<FoodItem>();
foodItemList.add(new FoodItem("Turkey Burger", GoodBad.HEALTHY, "burger"));
FragmentManager fm = getFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
for(FoodItem fi : foodItemList)
{
FoodItemDisplay fid = FoodItemDisplay.newInstance(fi.getName());
fid.setFoodItem(fi);
fid.setValues();
ft.add(R.id.healthyTab, fid);
}
ft.commit();
}
}
当我运行它时，我得到了这个堆栈跟踪：
java.lang.NullPointerException
at com.android.ddmlib.JdwpPacket.writeAndConsume(JdwpPacket.java:213)
at com.android.ddmlib.Client.sendAndConsume(Client.java:675)
at com.android.ddmlib.HandleHello.sendHELO(HandleHello.java:195)
at com.android.ddmlib.HandleHello.sendHelloCommands(HandleHello.java:66)
at com.android.ddmlib.Client.getJdwpPacket(Client.java:772)
at com.android.ddmlib.MonitorThread.processClientActivity(MonitorThread.java:317)
at com.android.ddmlib.MonitorThread.run(MonitorThread.java:263)
我在这个项目上做得很好，因为我可以看到堆栈跟踪到我写的代码并发现错误。但是当我点击这个时，它给了我没有写的代码的堆栈跟踪。我知道这表明我设置了一些错误的内容，但Google对此并没有太大的帮助，而且我已经多次使用此代码并且根据每个对象和类的文档没有看到任何错误我正在使用......有没有人曾经碰到过这个？也许对于要看什么有一些想法？或者直接得到答案？大声笑。我正在使用intellij-idea（不是android工作室）。
谢谢！ 乔恩
*来自下面的评论* 这是adb日志输出：
DeviceMonitor: Adb rejected connection to client '27925': closed
DeviceMonitor: Adb rejected connection to client '27952': closed
DeviceMonitor: Adb rejected connection to client '28560': closed
DeviceMonitor: Adb rejected connection to client '31166': closed
DeviceMonitor: Adb rejected connection to client '31790': closed
DeviceMonitor: Adb rejected connection to client '32138': closed
DeviceMonitor: Adb rejected connection to client '578': closed
DeviceMonitor: Adb rejected connection to client '578': closed
ddms: null
java.lang.NullPointerException
at com.android.ddmlib.JdwpPacket.writeAndConsume(JdwpPacket.java:213)
at com.android.ddmlib.Client.sendAndConsume(Client.java:675)
at com.android.ddmlib.HandleHello.sendHELO(HandleHello.java:195)
at com.android.ddmlib.HandleHello.sendHelloCommands(HandleHello.java:66)
at com.android.ddmlib.Client.getJdwpPacket(Client.java:772)
at com.android.ddmlib.MonitorThread.processClientActivity(MonitorThread.java:317)
at com.android.ddmlib.MonitorThread.run(MonitorThread.java:263)
ddms: null
java.lang.NullPointerException
at com.android.ddmlib.JdwpPacket.writeAndConsume(JdwpPacket.java:213)
at com.android.ddmlib.Client.sendAndConsume(Client.java:675)
at com.android.ddmlib.HandleHello.sendHELO(HandleHello.java:195)
at com.android.ddmlib.HandleHello.sendHelloCommands(HandleHello.java:66)
at com.android.ddmlib.Client.getJdwpPacket(Client.java:772)
at com.android.ddmlib.MonitorThread.processClientActivity(MonitorThread.java:317)
at com.android.ddmlib.MonitorThread.run(MonitorThread.java:263)
DeviceMonitor: Adb rejected connection to client '832': closed
DeviceMonitor: Adb rejected connection to client '3083': closed
DeviceMonitor: Adb rejected connection to client '5816': closed
DeviceMonitor: Adb rejected connection to client '5847': closed
DeviceMonitor: Adb rejected connection to client '6144': closed
PropertyFetcher: AdbCommandRejectedException getting properties for device LGUS990611b931f: device offline
PropertyFetcher: AdbCommandRejectedException getting properties for device LGUS990611b931f: device unauthorized. Please check the confirmation dialog on your device.
PropertyFetcher: AdbCommandRejectedException getting properties for device LGUS990611b931f: device unauthorized. Please check the confirmation dialog on your device.
PropertyFetcher: AdbCommandRejectedException getting properties for device LGUS990611b931f: device unauthorized. Please check the confirmation dialog on your device.
重新配置后出现新错误： 好的...现在出现新错误 - ＆gt;
Caused by: java.lang.IllegalArgumentException: No view found for id 0x7f09005a (com.thenewjonathan.foodtracker:id/healthyTab) for fragment FoodItemDisplay{b5abff #0 id=0x7f09005a}
at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:886)
at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067)
at android.app.BackStackRecord.run(BackStackRecord.java:833)
at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1452)
at android.app.Activity.performStart(Activity.java:6035)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2269)
at android.app.ActivityThread.startActivityNow(ActivityThread.java:2128)
at android.app.LocalActivityManager.moveToState(LocalActivityManager.java:135)
at android.app.LocalActivityManager.startActivity(LocalActivityManager.java:347)
at android.widget.TabHost$IntentContentStrategy.getContentView(TabHost.java:756)
at android.widget.TabHost.setCurrentTab(TabHost.java:420)
at android.widget.TabHost.addTab(TabHost.java:247)
at com.thenewjonathan.foodtracker.MainMenu.onCreate(MainMenu.java:30)
at android.app.Activity.performCreate(Activity.java:6020)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2259)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2368)
at android.app.ActivityThread.access$800(ActivityThread.java:149)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1284)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5299)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
当我尝试将“健康”标签添加到tabhost时，我的主菜单的oncreate正在添加选项卡：
public class MainMenu extends ActivityGroup
{
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
this.requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.main_menu);
TabHost container = (TabHost) findViewById(R.id.mainTabHost);
container.setup(this.getLocalActivityManager());
TabSpec healthy = container.newTabSpec("Healthy Foods").setContent(new Intent(this, HealthyFoods.class))
.setIndicator("Healthy Foods");
TabSpec unHealthy = container.newTabSpec("Unhealthy Foods").setContent(new Intent(this, UnHealthyFoods.class))
.setIndicator("Unhealthy Foods");
container.addTab(healthy);
container.addTab(unHealthy);
}
}
答案 0 :(得分：4)
您在片段类中onCreate()内部引用了错误的视图。您应该在onCreateView()内获取他们的引用，如下所示：
View view = inflater.inflate(R.layout.food_item_display, container, false);
itemNameView = (TextView) view.findViewById(R.id.foodItemNameView);
image = (ImageView) view.findViewById(R.id.foodPic);
你写它的方式，你试图在你给它们一个值之前引用它们，因此NPE。如果food_item_display实际上是所有这些项目的父布局，那么您应该使用该视图按ID查找其他项目，如我在此处所示。
答案 1 :(得分：2)
您必须使用onActivityCreated或onCreateView来获取以下示例等参考资料。您不能使用onCreate这样做，因为片段只会在onCreateView之后创建。
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
return inflater.inflate(R.layout.food_item_display, container, false);
}
@Override
public void onActivityCreated(Bundle savedInstanceState){
View _view = getView();
itemNameView = (TextView) _view.findViewById(R.id.foodItemNameView);
image = (ImageView) _view.findViewById(R.id.foodPic);
mondayBox = (CheckBox) _view.findViewById(R.id.mondayBox);
tuesdayBox = (CheckBox) _view.findViewById(R.id.tuesdayBox);
wednesdayBox = (CheckBox) _view.findViewById(R.id.wednesdayBox);
thursdayBox = (CheckBox) _view.findViewById(R.id.thursdayBox);
fridayBox = (CheckBox) _view.findViewById(R.id.fridayBox);
saturdayBox = (CheckBox) _view.findViewById(R.id.saturdayBox);
sundayBox = (CheckBox) _view.findViewById(R.id.sundayBox);
}
另一个例子：
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
View _view = inflater.inflate(R.layout.food_item_display, container, false);
itemNameView = (TextView) _view.findViewById(R.id.foodItemNameView);
image = (ImageView) _view.findViewById(R.id.foodPic);
mondayBox = (CheckBox) _view.findViewById(R.id.mondayBox);
tuesdayBox = (CheckBox) _view.findViewById(R.id.tuesdayBox);
wednesdayBox = (CheckBox) _view.findViewById(R.id.wednesdayBox);
thursdayBox = (CheckBox) _view.findViewById(R.id.thursdayBox);
fridayBox = (CheckBox) _view.findViewById(R.id.fridayBox);
saturdayBox = (CheckBox) _view.findViewById(R.id.saturdayBox);
sundayBox = (CheckBox) _view.findViewById(R.id.sundayBox);
return _view;
}