java - findViewById(R.id.view_id) 在复合 View 的情况下返回 null

Question

复合 View xml代码:-

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/dayRelativeLayout"
    android:layout_width="30dip"
    android:layout_height="45dip"
    android:background="@drawable/selectable_day_layout_border">

   <TextView android:id="@+id/eventTextView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:textSize="12dip"
        android:visibility="invisible"
        android:layout_margin="2.1dip"
        android:textAppearance="?android:attr/textAppearanceSmall"/>

    <TextView
        android:id="@+id/dayTextView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:layout_gravity="center"
        android:layout_below="@+id/eventTextView"
        android:textAppearance="?android:attr/textAppearanceSmall"/>
</RelativeLayout>

下面是上述复合控件的java代码:-

public class CalendarGridView extends RelativeLayout
{
    private Context context = null;

    private TextView eventTextView = null;

    private TextView dayTextView = null;

    public CalendarGridView(Context context)
    {
        super(context);

        this.context = context;

        init();
    }

    public CalendarGridView(Context context, AttributeSet attrs)
    {
        super(context, attrs);
        this.context = context;
        init();
    }

    public CalendarGridView(Context context, AttributeSet attrs,int defStyle)
    {
        super(context, attrs, defStyle);
        this.context = context;
        init();
    }

    private void init()
    {
        int id = (int)Math.abs(Math.random()*100000);

        super.setId(id);

        LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        addView(inflater.inflate(R.layout.day_view, null));

        eventTextView = (TextView) findViewById(R.id.eventTextView);

        dayTextView = (TextView) findViewById(R.id.dayTextView);

        eventTextView.setOnClickListener(new GridClickListener());

        dayTextView.setOnClickListener(new GridClickListener());
    }

    public TextView getEventTextView()
    {
        return eventTextView;
    }

    public TextView getDayTextView()
    {
        return dayTextView;
    }

    class GridClickListener implements OnClickListener
    {
        @Override
        public void onClick(View v)
        {
            calculateClickedGrid(v);
        }
    }

    private void calculateClickedGrid(View v)
    {
        int id = ((ViewGroup)v.getParent()).getId();

        GridCordinates cordinates = GridViewUtil.getGridCordinate(id);

        if(cordinates != null)
        {

        }
    }
}

下面是我在其中使用上述复合控件的 gridlayout xml 代码:-

<?xml version="1.0" encoding="utf-8"?>
<GridLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content" android:layout_height="wrap_content"
    android:rowCount="8"
    android:columnCount="7"
    android:background="@drawable/selectable_day_layout_border">

    <!-- Row 0-->
    <ImageButton
        android:id="@+id/previousMonthImageButton"
        android:layout_row="0"
        android:layout_columnSpan="1"
        android:layout_column="0"
        android:layout_gravity="center"
        android:layout_margin="3dip"
        android:padding="3dip"
        android:background="#7F7CD9"
        android:src="@drawable/navigation_previous_item"/>
    <TextView
        android:id="@+id/monthNameTextView"
        android:text="September"
        android:layout_row="0"
        android:layout_columnSpan="5"
        android:layout_column="1"
        android:layout_gravity="center"
        android:layout_margin="3dip"
        android:padding="3dip"
        android:textSize="25dip"
        android:background="#7F7CD9"/>

    <ImageButton
        android:id="@+id/nextMonthImageButton"
        android:layout_row="0"
        android:layout_columnSpan="1"
        android:layout_column="6"
        android:layout_gravity="center"
        android:layout_margin="3dip"
        android:padding="3dip"
        android:background="#7F7CD9"
        android:src="@drawable/navigation_next_item"/>

    <!-- Row 1-->

    <com.gp.app.minote.calendar.ui.CalendarGridView
        android:id="@+id/day1"
        android:layout_row="2"
        android:layout_column="0"
        android:layout_width="30dip"
        android:layout_height="40dip"
        android:layout_margin="2dip"
        android:padding="3dip"
        android:layout_gravity="center"
        android:background="@drawable/selectable_day_layout_border"/>

    <com.gp.app.minote.calendar.ui.CalendarGridView
        android:layout_width="30dip"
        android:layout_height="40dip"
        android:id="@+id/day2"
        android:layout_row="2"
        android:layout_column="1"
        android:layout_margin="2dip"
        android:padding="3dip"
        android:layout_gravity="center"
        android:background="@drawable/selectable_day_layout_border"/>

    <com.gp.app.minote.calendar.ui.CalendarGridView
        android:layout_width="30dip"
        android:layout_height="40dip"
        android:id="@+id/day3"
        android:layout_row="2"
        android:layout_column="2"
        android:layout_margin="2dip"
        android:layout_gravity="center"
        android:padding="3dip"
        android:background="@drawable/selectable_day_layout_border"/>

<!--  More CalendarGridViews but deleted for clarity -->
</GridLayout>

下面提到的是扩展 GridLayout 并使用 CalendarGridViews 的类的代码:-

public class ProfessionalPACalendarView extends GridLayout
{
    private Context context;
    private Calendar cal;
    private ImageButton previousMonthImageButton = null;
    private ImageButton nextMonthImageButton = null;
    private TextView monthNameTextView = null;
    private List<DateInformation> dateList = new ArrayList<>();
    private List<CalendarGridView> calendarGrids = new ArrayList<>();
    private RelativeLayout base;
    private ImageView next,prev;
    private boolean isWithoutEvents = false;
    private int id = 0;

    public ProfessionalPACalendarView(Context context)
    {
        super(context);
        this.context = context;
        cal= Calendar.getInstance();

        if(!isWithoutEvents)
        {
            CalendarDBManager.getInstance().addDataChangeListener(this);
        }

        initView();
        this.isWithoutEvents = isWithoutEvents;
    }

    public ProfessionalPACalendarView(Context context, AttributeSet attrs) {
        super(context, attrs);
        this.context = context;
        initView();
    }

    public ProfessionalPACalendarView(Context context, AttributeSet attrs,int defStyle)
    {
        super(context, attrs, defStyle);
        this.context = context;
        initView();
    }

    private void initView()
    {
        init();

        Calendar calendar = Calendar.getInstance();
        refreshDays(calendar.get(Calendar.DATE), calendar.get(Calendar.MONTH), calendar.get(Calendar.YEAR));
        fillCalendarViewWithDates();
    }

    private void init()
    {
        int id = (int)Math.abs(Math.random() * 100000);

        super.setId(id);

        LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        View view = inflater.inflate(R.layout.calendar_grid_layout, null);

        addView(view);

        previousMonthImageButton = (ImageButton) findViewById(R.id.previousMonthImageButton);

        previousMonthImageButton.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v)
            {
                previousMonth();
            }
        });

        monthNameTextView = (TextView) findViewById(R.id.monthNameTextView);

        nextMonthImageButton = (ImageButton) findViewById(R.id.nextMonthImageButton);

        nextMonthImageButton.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                nextMonth();
            }
        });

        calendarGrids.add((CalendarGridView) findViewById(R.id.day2));
        calendarGrids.add((CalendarGridView) findViewById(R.id.day3));
}

问题:- findViewById(id) 在下面的行中:-

previousMonthImageButton =(ImageButton)findViewById(R.id.previousMonthImageButton);

monthNameTextView = (TextView) findViewById(R.id.monthNameTextView);

nextMonthImageButton = (ImageButton) findViewById(R.id.nextMonthImageButton);

返回非空值，而 findViewById(id) 在下面的行中:-

calendarGrids.add((CalendarGridView) findViewById(R.id.day2));
calendarGrids.add((CalendarGridView) findViewById(R.id.day3));

返回空值。

我已经尝试了很长时间来解决这个问题，但没有明白为什么相同的方法会为不同的 View 返回空值和非空值。我认为这与复合 View 有关。请帮忙。

Answer 1

你初始化View view = inflater.inflate(R.layout.calendar_grid_layout, null);

请传递 View Object 。

      previousMonthImageButton =(ImageButton)view.findViewById(R.id.previousMonthImageButton);
      monthNameTextView = (TextView)view. findViewById(R.id.monthNameTextView);
      nextMonthImageButton = (ImageButton)view.findViewById(R.id.nextMonthImageButton);

试试这个方法，希望对你有帮助。