将 XML 对象传递给外部函数 (Android)

Question

我想以编程方式（不包括 XML 的方式）添加我在外部 XML 中创建的 RelativeLayout，然后从外部函数对其进行设置。

错误如下：

FATAL EXCEPTION: main
Process: ucam, PID: 8950
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setId(int)' on a null object reference
at ucam.misc.MessageSetter.setMessageInfo(MessageSetter.java:51)
at ucam.activities.MainBoard$3$1.onSuccess(MainBoard.java:133)
at ucam.misc.RequestManager$1.onResponse(RequestManager.java:58)
at ucam.misc.RequestManager$1.onResponse(RequestManager.java:43)                                 
at com.android.volley.toolbox.JsonRequest.deliverResponse(JsonRequest.java:65)
at com.android.volley.ExecutorDelivery$ResponseDeliveryRunnable.run(ExecutorDelivery.java:99)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

这是 mainactivity.java 中的代码：

private Message m;
private List<Message> ml;
private TextView textBox, dateBox, likesBox, textTitle;
private ImageButton likeButton;
private LinearLayout content, main;
private RelativeLayout news;
private MessageSetter msetter;
private RequestManager rmanager;


@Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main_board);

        news = (RelativeLayout) findViewById(R.id.news_template);

(...)

@Override
        public boolean onNavigationItemSelected(@NonNull MenuItem item) {
            switch (item.getItemId()) {
                case R.id.navigation_recents:
                    rmanager.getRecentMessages(new VolleyCallbackOp() {

                        public void onSuccess(List<Message> ml) {
                            for (int a = 0; a < ml.size(); a++) {

                                Message j = ml.get(a);
                                msetter = new MessageSetter(MainBoard.this);
                                View v = msetter.setMessageInfo(j, a);



                                });

                                content.addView(v);
                            }
                        }
                    });

这是外部设置器类：

public class MessageSetter {
    public Activity mainBoard;
    private TextView textBox, dateBox, likesBox, textTitle;
    private ImageButton likeButton;
    private RelativeLayout news;



    public MessageSetter(Activity mainBoard) {
        this.mainBoard = mainBoard;
        this.news = (RelativeLayout) this.mainBoard.findViewById(R.id.news_template);
        this.textBox = (TextView) this.mainBoard.findViewById(R.id.text_box);
        this.dateBox = (TextView) this.mainBoard.findViewById(R.id.date_box);
        this.likesBox = (TextView) this.mainBoard.findViewById(R.id.likes_box);
        this.textTitle = (TextView) this.mainBoard.findViewById(R.id.text_title);

    }

    public View setMessageInfo(Message j, int a) {
        int idDB = a;
        int idLB = a;
        int idLBT = a;
        textTitle.setId(a);
        textTitle.setText(j.getTitle());
        textBox.setText(j.getContent());
        textBox.setId((j.getId()));
        dateBox.setText(String.valueOf(j.getDate()));
        dateBox.setId(idDB);
        likesBox.setText(String.valueOf(j.getLikesCount()));
        likesBox.setId(idLB);

return news;
    }

这是 mainactivity 布局：

<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout
    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:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context=".activities.MainBoard"
    tools:openDrawer="start">



<ScrollView
    android:id="@+id/main_scroll"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <LinearLayout

        android:id="@+id/main_linear"
        android:orientation="vertical"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <include layout="@layout/app_bar_main_board" />

        <LinearLayout
            android:id="@+id/main_content"
            android:orientation="vertical"
            android:layout_width="match_parent"
            android:layout_height="wrap_content">

        </LinearLayout>


    </LinearLayout>

</ScrollView>

    <android.support.design.widget.CoordinatorLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <android.support.design.widget.BottomNavigationView
            android:id="@+id/navigation"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_gravity="bottom"
            android:background="?android:attr/windowBackground"
            app:menu="@menu/navigation" />

        <android.support.design.widget.FloatingActionButton
            android:id="@+id/fab"
            android:layout_width="wrap_content"
            android:layout_height="72dp"
            android:layout_gravity="center|end"
            android:layout_margin="@dimen/fab_margin"
            app:srcCompat="@drawable/ic_comment_black_24dp" />

    </android.support.design.widget.CoordinatorLayout>

    <android.support.design.widget.NavigationView

        android:id="@+id/nav_view"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        app:headerLayout="@layout/nav_header_main_board"
        app:menu="@menu/activity_main_board_drawer" >

    </android.support.design.widget.NavigationView>


</android.support.v4.widget.DrawerLayout>

最后这是我要设置并包含在活动中的 XML 外部布局文件：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_marginTop="3dp"
    android:layout_marginRight="3dp"
    android:layout_marginLeft="3dp"
    android:id="@+id/news_template"
    android:layout_width="match_parent"
    android:layout_height="120dp"
    android:background="#5A8FF2"
    android:orientation="horizontal"
    tools:context=".activities.MainBoard">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="2dp"
        android:id="@+id/text_title"
        android:textColor="#000000"
        android:textStyle="normal"
        android:textSize="14dp"
        android:gravity="center"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true" />
    <TextView
        android:id="@+id/text_box"
        android:textColor="#000000"
        android:textStyle="normal"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="14dp"
        android:padding="10dp"
        android:layout_above="@+id/news_answers"
        android:layout_below="@+id/text_title"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true">
    </TextView>

    <LinearLayout
        android:id="@+id/news_answers"
        android:layout_width="20dp"
        android:layout_height="20dp"
        android:layout_alignParentBottom="true"
        android:layout_alignParentLeft="true"
        android:layout_marginBottom="15dp"
        android:layout_marginLeft="25dp"
        android:orientation="horizontal">

    </LinearLayout>

    <LinearLayout
        android:id="@+id/news_likes"
        android:layout_marginRight="8dp"
        android:layout_width="120dp"
        android:layout_height="match_parent"
        android:layout_alignParentBottom="true"
        android:layout_alignTop="@+id/imageView2"
        android:gravity="right"
        android:orientation="vertical"
        android:weightSum="2"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="0dp"
            android:layout_weight="1"
            android:textSize="12dp"
            android:text="Likes" />

        <TextView
            android:id="@+id/likes_box"
            android:textSize="12dp"
            android:layout_width="wrap_content"
            android:layout_height="0dp"
            android:layout_weight="1" />
    </LinearLayout>

    <ImageButton
        android:id="@+id/like_button"
        android:layout_width="26dp"
        android:layout_height="26dp"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        android:background="@drawable/ic_mood_black_24dp"
        android:text="Like" />

    <LinearLayout
        android:id="@+id/imageView2"
        android:layout_marginLeft="8dp"
        android:layout_width="120dp"
        android:layout_height="match_parent"
        android:layout_alignParentBottom="true"
        android:layout_alignTop="@+id/news_answers"
        android:orientation="vertical"
        android:weightSum="2">

        <TextView
            android:layout_width="wrap_content"
            android:textSize="12dp"
            android:layout_height="0dp"
            android:layout_weight="1"
            android:text="Date" />

        <TextView
            android:id="@+id/date_box"
            android:textSize="12dp"
            android:layout_width="wrap_content"
            android:layout_height="0dp"
            android:layout_weight="1" />
    </LinearLayout>

</RelativeLayout>

我不明白为什么 setfunction 返回一个空引用..

Answer 1

发生这种情况的原因是您以错误的方式使用findViewById()。

this.news = (RelativeLayout) this.mainBoard.findViewById(R.id.news_template);
this.textBox = (TextView) this.mainBoard.findViewById(R.id.text_box);
this.dateBox = (TextView) this.mainBoard.findViewById(R.id.date_box);
this.likesBox = (TextView) this.mainBoard.findViewById(R.id.likes_box);
this.textTitle = (TextView) this.mainBoard.findViewById(R.id.text_title);

所有这些方法调用都返回 null，因为这些视图不在您的活动布局中 - 您在此处设置的 R.layout.activity_main_board setContentView(R.layout.activity_main_board);

相反，您应该单独使用扩展您的 xml 布局，然后他们会从该 xml 中找到视图。 查看此代码：

//get the inflater from your activity
LayoutInflater inflater = mainBoard.getLayoutInflater();
//get the root view, this is the view that should be the parent of the new inflated view
View root = this.mainBoard.findViewById(R.id.main_content);
//false indicates that the new inflated view wont be attatched to its parent. Use true if this is not your wanted behavior
this.news = (RelativeLayout) = inflater.inflate(R.layout.news_template, (ViewGroup) root,false); 
//find the views from the inflated xml
this.textBox = (TextView) news.findViewById(R.id.text_box);
this.dateBox = (TextView) news.findViewById(R.id.date_box);
this.likesBox = (TextView) news.findViewById(R.id.likes_box);
this.textTitle = (TextView) news.findViewById(R.id.text_title);