尝试在数组中的 fragmenrt 上填充 Xamarin Android TextView 时，对象引用未设置为对象的实例

Question

当我尝试从片段中引用 TextView 时出现错误 System.NullReferenceException: Object reference not set to an instance of an object。它发生在运行时。

片段

public class Fragment1 : Fragment
{
    private int checkNumber = 0;
    private string[] updateTitleArray = new string[10];
    private string[] updateBodyArray = new string[10];
    private TextView updatesTitle0;
    private TextView updatesTitle1;
    private TextView updatesTitle2;
    private TextView updatesTitle3;
    private TextView updatesTitle4;
    private TextView updatesTitle5;
    private TextView updatesTitle6;
    private TextView updatesTitle7;
    private TextView updatesTitle8;
    private TextView updatesTitle9;

    private TextView updateBody0;
    private TextView updateBody1;
    private TextView updateBody2;
    private TextView updateBody3;
    private TextView updateBody4;
    private TextView updateBody5;
    private TextView updateBody6;
    private TextView updateBody7;
    private TextView updateBody8;
    private TextView updateBody9;



    public override void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);
        fillUpdates(updateTitleArray, updateBodyArray);
    }

    public static Fragment1 NewInstance()
    {
        var frag1 = new Fragment1 { Arguments = new Bundle() };
        return frag1;
    }


    public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        var ignored = base.OnCreateView(inflater, container, savedInstanceState);
        return inflater.Inflate(Resource.Layout.fragment1, null);
    }

    public void fillUpdates(string[] updatetitlearray, string[] updatebodyarray)
    {
        //increment1 so if block skips here
        checkNumber = 1;

        //fill updatesArray
        updateTitleArray = updatetitlearray;
        updateBodyArray = updatebodyarray;

        updatesTitle0 = View.FindViewById<TextView>(Resource.Id.update_title0);
        updatesTitle1 = View.FindViewById<TextView>(Resource.Id.update_title1);
        updatesTitle2 = View.FindViewById<TextView>(Resource.Id.update_title2);
        updatesTitle3 = View.FindViewById<TextView>(Resource.Id.update_title3);
        updatesTitle4 = View.FindViewById<TextView>(Resource.Id.update_title4);
        updatesTitle5 = View.FindViewById<TextView>(Resource.Id.update_title5);
        updatesTitle6 = View.FindViewById<TextView>(Resource.Id.update_title6);
        updatesTitle7 = View.FindViewById<TextView>(Resource.Id.update_title7);
        updatesTitle8 = View.FindViewById<TextView>(Resource.Id.update_title8);
        updatesTitle9 = View.FindViewById<TextView>(Resource.Id.update_title9);

        updateBody0 = View.FindViewById<TextView>(Resource.Id.update_body0);
        updateBody1 = View.FindViewById<TextView>(Resource.Id.update_body1);
        updateBody2 = View.FindViewById<TextView>(Resource.Id.update_body2);
        updateBody3 = View.FindViewById<TextView>(Resource.Id.update_body3);
        updateBody4 = View.FindViewById<TextView>(Resource.Id.update_body4);
        updateBody5 = View.FindViewById<TextView>(Resource.Id.update_body5);
        updateBody6 = View.FindViewById<TextView>(Resource.Id.update_body6);
        updateBody7 = View.FindViewById<TextView>(Resource.Id.update_body7);
        updateBody8 = View.FindViewById<TextView>(Resource.Id.update_body8);
        updateBody9 = View.FindViewById<TextView>(Resource.Id.update_body9);


        updatesTitle0.Text = updateTitleArray[0].ToString();
        updatesTitle1.Text = updateTitleArray[1].ToString();
        updatesTitle2.Text = updateTitleArray[2].ToString();
        updatesTitle3.Text = updateTitleArray[3].ToString();
        updatesTitle4.Text = updateTitleArray[4].ToString();
        updatesTitle5.Text = updateTitleArray[5].ToString();
        updatesTitle6.Text = updateTitleArray[6].ToString();
        updatesTitle7.Text = updateTitleArray[7].ToString();
        updatesTitle8.Text = updateTitleArray[8].ToString();
        updatesTitle9.Text = updateTitleArray[9].ToString();

        updateBody0.Text = updateBodyArray[0].ToString();
        updateBody1.Text = updateBodyArray[1].ToString();
        updateBody2.Text = updateBodyArray[2].ToString();
        updateBody3.Text = updateBodyArray[3].ToString();
        updateBody4.Text = updateBodyArray[4].ToString();
        updateBody5.Text = updateBodyArray[5].ToString();
        updateBody6.Text = updateBodyArray[6].ToString();
        updateBody7.Text = updateBodyArray[7].ToString();
        updateBody8.Text = updateBodyArray[8].ToString();
        updateBody9.Text = updateBodyArray[9].ToString();
    }
}

查看

   <ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        android:padding="10dp"
        android:fillViewport="false">
        <LinearLayout
            android:orientation="vertical"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent">
        <!--Cardview 1-->
            <android.support.v7.widget.CardView xmlns:card_view="http://schemas.android.com/apk/res-auto"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:minHeight="60dp"
                card_view:cardElevation="8dp"
                card_view:cardCornerRadius="8dp"
                android:layout_marginLeft="8dp"
                android:layout_marginRight="8dp"
                android:layout_marginTop="8dp">
                <GridLayout
                    android:minWidth="25px"
                    android:minHeight="25px"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:columnCount="3"
                    android:rowCount="1">
                    <LinearLayout
                        android:orientation="vertical"
                        android:layout_gravity="fill"
                        android:layout_row="0"
                        android:layout_column="0"
                        android:padding="16sp">
                        <TextView
                            android:id="@+id/update_title0"
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:text="Update 1"
                            android:padding="4sp"
                            android:textSize="24sp"
                            android:textColor="@color/primaryText" />
                        <TextView
                            android:id="@+id/update_body0"
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:text="Update Details Is Shownbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb Here"
                            android:padding="4sp"
                            android:textSize="16sp" />
                    </LinearLayout>
                </GridLayout>
            </android.support.v7.widget.CardView>
        <!--card view2-->
            <android.support.v7.widget.CardView xmlns:card_view="http://schemas.android.com/apk/res-auto"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                card_view:cardElevation="8dp"
                card_view:cardCornerRadius="8dp"
                android:layout_marginLeft="8dp"
                android:layout_marginRight="8dp"
                android:layout_marginTop="8dp">
                <GridLayout
                    android:minWidth="25px"
                    android:minHeight="25px"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:columnCount="3"
                    android:rowCount="1">
                    <LinearLayout
                        android:orientation="vertical"
                        android:layout_gravity="fill"
                        android:layout_row="0"
                        android:layout_column="0"
                        android:padding="16sp">
                        <TextView
                            android:id="@+id/update_title1"
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:text="Update 1"
                            android:padding="4sp"
                            android:textSize="24sp"
                            android:textColor="@color/primaryText" />
                        <TextView
                            android:id="@+id/update_body1"
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:text="Update Details Is Shown Here"
                            android:padding="4sp"
                            android:textSize="16sp" />
                    </LinearLayout>
                </GridLayout>
            </android.support.v7.widget.CardView>
        <!--cardview 3-->
            <android.support.v7.widget.CardView xmlns:card_view="http://schemas.android.com/apk/res-auto"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                card_view:cardElevation="8dp"
                card_view:cardCornerRadius="8dp"
                android:layout_marginLeft="8dp"
                android:layout_marginRight="8dp"
                android:layout_marginTop="8dp">
                <GridLayout
                    android:minWidth="25px"
                    android:minHeight="25px"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:columnCount="3"
                    android:rowCount="1">
                    <LinearLayout
                        android:orientation="vertical"
                        android:layout_gravity="fill"
                        android:layout_row="0"
                        android:layout_column="0"
                        android:padding="16sp">
                        <TextView
                            android:id="@+id/update_title2"
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:text="Update 1"
                            android:padding="4sp"
                            android:textSize="24sp"
                            android:textColor="@color/primaryText" />
                        <TextView
                            android:id="@+id/update_body2"
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:text="Update Details Is Shown Here"
                            android:padding="4sp"
                            android:textSize="16sp" />
                    </LinearLayout>
                </GridLayout>
            </android.support.v7.widget.CardView>
        <!--card view 4-->
            <android.support.v7.widget.CardView xmlns:card_view="http://schemas.android.com/apk/res-auto"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                card_view:cardElevation="8dp"
                card_view:cardCornerRadius="8dp"
                android:layout_marginLeft="8dp"
                android:layout_marginRight="8dp"
                android:layout_marginTop="8dp">
                <GridLayout
                    android:minWidth="25px"
                    android:minHeight="25px"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:columnCount="3"
                    android:rowCount="1">
                    <LinearLayout
                        android:orientation="vertical"
                        android:layout_gravity="fill"
                        android:layout_row="0"
                        android:layout_column="0"
                        android:padding="16sp">
                        <TextView
                            android:id="@+id/update_title3"
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:text="Update 1"
                            android:padding="4sp"
                            android:textSize="24sp"
                            android:textColor="@color/primaryText" />
                        <TextView
                            android:id="@+id/update_body3"
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:text="Update Details Is Shown Here"
                            android:padding="4sp"
                            android:textSize="16sp" />
                    </LinearLayout>
                </GridLayout>
            </android.support.v7.widget.CardView>
        <!--card view 5-->
            <android.support.v7.widget.CardView xmlns:card_view="http://schemas.android.com/apk/res-auto"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                card_view:cardElevation="8dp"
                card_view:cardCornerRadius="8dp"
                android:layout_marginLeft="8dp"
                android:layout_marginRight="8dp"
                android:layout_marginTop="8dp">
                <GridLayout
                    android:minWidth="25px"
                    android:minHeight="25px"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:columnCount="3"
                    android:rowCount="1">
                    <LinearLayout
                        android:orientation="vertical"
                        android:layout_gravity="fill"
                        android:layout_row="0"
                        android:layout_column="0"
                        android:padding="16sp">
                        <TextView
                            android:id="@+id/update_title4"
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:text="Update 1"
                            android:padding="4sp"
                            android:textSize="24sp"
                            android:textColor="@color/primaryText" />
                        <TextView
                            android:id="@+id/update_body4"
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:text="Update Details Is Shown Here"
                            android:padding="4sp"
                            android:textSize="16sp" />
                    </LinearLayout>
                </GridLayout>
            </android.support.v7.widget.CardView>
        <!--card view 6-->
            <android.support.v7.widget.CardView xmlns:card_view="http://schemas.android.com/apk/res-auto"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                card_view:cardElevation="8dp"
                card_view:cardCornerRadius="8dp"
                android:layout_marginLeft="8dp"
                android:layout_marginRight="8dp"
                android:layout_marginTop="8dp">
                <GridLayout
                    android:minWidth="25px"
                    android:minHeight="25px"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:columnCount="3"
                    android:rowCount="1">
                    <LinearLayout
                        android:orientation="vertical"
                        android:layout_gravity="fill"
                        android:layout_row="0"
                        android:layout_column="0"
                        android:padding="16sp">
                        <TextView
                            android:id="@+id/update_title5"
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:text="Update 1"
                            android:padding="4sp"
                            android:textSize="24sp"
                            android:textColor="@color/primaryText" />
                        <TextView
                            android:id="@+id/update_body5"
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:text="Update Details Is Shown Here"
                            android:padding="4sp"
                            android:textSize="16sp" />
                    </LinearLayout>
                </GridLayout>
            </android.support.v7.widget.CardView>
        <!--card view 7-->
            <android.support.v7.widget.CardView xmlns:card_view="http://schemas.android.com/apk/res-auto"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                card_view:cardElevation="8dp"
                card_view:cardCornerRadius="8dp"
                android:layout_marginLeft="8dp"
                android:layout_marginRight="8dp"
                android:layout_marginTop="8dp">
                <GridLayout
                    android:minWidth="25px"
                    android:minHeight="25px"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:columnCount="3"
                    android:rowCount="1">
                    <LinearLayout
                        android:orientation="vertical"
                        android:layout_gravity="fill"
                        android:layout_row="0"
                        android:layout_column="0"
                        android:padding="16sp">
                        <TextView
                            android:id="@+id/update_title6"
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:text="Update 1"
                            android:padding="4sp"
                            android:textSize="24sp"
                            android:textColor="@color/primaryText" />
                        <TextView
                            android:id="@+id/update_body6"
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:text="Update Details Is Shown Here"
                            android:padding="4sp"
                            android:textSize="16sp" />
                    </LinearLayout>
                </GridLayout>
            </android.support.v7.widget.CardView>
        <!--card view 8-->
            <android.support.v7.widget.CardView xmlns:card_view="http://schemas.android.com/apk/res-auto"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                card_view:cardElevation="8dp"
                card_view:cardCornerRadius="8dp"
                android:layout_marginLeft="8dp"
                android:layout_marginRight="8dp"
                android:layout_marginTop="8dp">
                <GridLayout
                    android:minWidth="25px"
                    android:minHeight="25px"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:columnCount="3"
                    android:rowCount="1">
                    <LinearLayout
                        android:orientation="vertical"
                        android:layout_gravity="fill"
                        android:layout_row="0"
                        android:layout_column="0"
                        android:padding="16sp">
                        <TextView
                            android:id="@+id/update_title7"
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:text="Update 1"
                            android:padding="4sp"
                            android:textSize="24sp"
                            android:textColor="@color/primaryText" />
                        <TextView
                            android:id="@+id/update_body7"
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:text="Update Details Is Shown Here"
                            android:padding="4sp"
                            android:textSize="16sp" />
                    </LinearLayout>
                </GridLayout>
            </android.support.v7.widget.CardView>
        <!--card view 9-->
            <android.support.v7.widget.CardView xmlns:card_view="http://schemas.android.com/apk/res-auto"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                card_view:cardElevation="8dp"
                card_view:cardCornerRadius="8dp"
                android:layout_marginLeft="8dp"
                android:layout_marginRight="8dp"
                android:layout_marginTop="8dp">
                <GridLayout
                    android:minWidth="25px"
                    android:minHeight="25px"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:columnCount="3"
                    android:rowCount="1">
                    <LinearLayout
                        android:orientation="vertical"
                        android:layout_gravity="fill"
                        android:layout_row="0"
                        android:layout_column="0"
                        android:padding="16sp">
                        <TextView
                            android:id="@+id/update_title8"
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:text="Update 1"
                            android:padding="4sp"
                            android:textSize="24sp"
                            android:textColor="@color/primaryText" />
                        <TextView
                            android:id="@+id/update_body8"
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:text="Update Details Is Shown Here"
                            android:padding="4sp"
                            android:textSize="16sp" />
                    </LinearLayout>
                </GridLayout>
            </android.support.v7.widget.CardView>
        <!--card view 10-->
            <android.support.v7.widget.CardView xmlns:card_view="http://schemas.android.com/apk/res-auto"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                card_view:cardElevation="8dp"
                card_view:cardCornerRadius="8dp"
                android:layout_marginLeft="8dp"
                android:layout_marginRight="8dp"
                android:layout_marginTop="8dp">
                <GridLayout
                    android:minWidth="25px"
                    android:minHeight="25px"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:columnCount="3"
                    android:rowCount="1">
                    <LinearLayout
                        android:orientation="vertical"
                        android:layout_gravity="fill"
                        android:layout_row="0"
                        android:layout_column="0"
                        android:padding="16sp">
                        <TextView
                            android:id="@+id/update_title9"
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:text="Update 1"
                            android:padding="4sp"
                            android:textSize="24sp"
                            android:textColor="@color/primaryText" />
                        <TextView
                            android:id="@+id/update_body9"
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            android:text="Update Details Is Shown Here"
                            android:padding="4sp"
                            android:textSize="16sp" />
                    </LinearLayout>
                </GridLayout>
            </android.support.v7.widget.CardView>
        </LinearLayout>
    </ScrollView>

我知道我想要实现的目标可以用回收器视图来实现，但我还没有完全理解，因为我是一个初学者程序员。

Answer 1

你说你的功能太早了。 OnCreate 在 OnCreateView 之前被调用。这意味着，当您尝试访问布局组件时，您的视图尚未创建。您必须将 fillUpdates 的调用移动到 OnStart（或 OnCreateView 或在 OnCreateView 之后调用的其他生命周期方法）。看看 Frament Lifecycle

public override void OnStart(Bundle bundle)
{
    base.OnStart(bundle);
    fillUpdates(updateTitleArray, updateBodyArray);
}

尝试在数组中的 fragmenrt 上填充 Xamarin Android TextView 时，对象引用未设置为对象的实例

Object reference not set to an instance of an object when trying to populate Xamarin Android TextView on fragmenrt from arrary

android

xamarin.android

android-fragments

xamarin

fragment-lifecycle