java - Android fragment 实现问题

Question

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);
    }
}

Answer 1

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。