这是我的 fragment 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>
这是我的 fragment 的 java 文件:(FoodItem 只是一个自定义对象，我用它来存储关于 fragment 所代表的每个食品的信息)
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;
}
}
这是我用来放置 fragment 的类:
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，因为我可以看到我编写的代码中的堆栈跟踪并发现错误。但是当我点击这个时，它为我提供了我没有编写的代码的堆栈跟踪。我知道这表明我设置了错误，但谷歌对此帮助不大，我已经多次查看这段代码，根据我对每个对象和类的文档，我没有发现任何错误正在使用...以前有没有人遇到过这个？也许对要看什么有一些想法？还是直截了本地回答？哈哈。我正在使用 intellij-idea(不是 android studios)。
谢谢! 乔恩
* 来自以下评论 * 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 ->
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)
它发生在我的主菜单的 oncreate 中，当我尝试将“健康”选项卡添加到 tabhost 时添加选项卡:
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);
}
}
最佳答案
您在 fragment 类的 onCreate() 中错误地引用了您的 View 。您应该在 onCreateView() 中获取它们的引用，执行如下操作:
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);
按照您的编写方式，您试图在给 View 赋值之前引用 View ，因此是 NPE。如果 food_item_display 实际上是所有这些项目的父布局，您应该使用该 View 通过 ID 查找其他项目，如我在此处所示。
关于java - Android fragment 实现问题，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/31190965/