Question

我是移动开发的新手。我正在使用visual studio 2015在xamarin中使用android。现在我正在关注sample code并按照其中所述进行操作。

我尝试在text布局中为edit text分配update值时收到异常。 Bellow是我将值分配给edit text

的代码

void List_ItemClick(object sender, AdapterView.ItemClickEventArgs e)
    {
        click_Employee = e.Position + 1;
        ICursor c = dbHelper.getSingleEntry(click_Employee);
        c.MoveToFirst();
        name = c.GetString(c.GetColumnIndex(dbHelper.EMPLOYEE_NAME));
        email = c.GetString(c.GetColumnIndex(dbHelper.EMPLOYEE_EMAIL));
        phone = c.GetString(c.GetColumnIndex(dbHelper.EMPLOYEE_PHONE));
        designation = c.GetString(c.GetColumnIndex(dbHelper.EMPLOYEE_DESIGNATION));
        dName.Text = name;
        dEmail.Text = email;
        dPhone.Text = phone;
        dDesignation.Text = designation;
    }

在上面的代码中，dName.Text = name;引发了异常.Bellow是错误描述

System.NullReferenceException: Object reference not set to an instance of an object.

我的show complete data函数执行了相同的工作，但事情很好，不知道update函数中发生了什么

更新1

Bellow是我的insert employee代码

namespace AppwithDB.Resources
{
[Activity(Label = "insertEmployee")]
class insertEmployee : Activity
{
    EditText name, email, phone, designation;
    Button submitBtn;
    private SQLiteHelper dbHelper;

    protected override void OnCreate(Bundle bundle)
    {
        base.OnCreate(bundle);

        //Create your app here 

        SetContentView(Resource.Layout.insert);
        initialize();
        dbHelper = new SQLiteHelper(this);
        submitBtn.Click += submitBtn_Click;
    }


    private void submitBtn_Click(object sender, EventArgs e)
    {
        if (name.Text.ToString().Equals("") || email.Text.ToString().Equals("")|| phone.Text.ToString().Equals("") || designation.Text.ToString().Equals(""))
        {
            Toast.MakeText(this, "Fields Empty Found", ToastLength.Short).Show();
        }
        else
        {
            dbHelper.insertEmployee(name.Text.ToString(), email.Text.ToString(), phone.Text.ToString(), designation.Text.ToString());
            Toast.MakeText(this, "Data Stored Successfully", ToastLength.Short).Show();
            name.Text = " ";
            email.Text = " ";
            phone.Text = " ";
            designation.Text = " ";
        }
    }

    private void initialize()
    {
        name = (EditText)FindViewById(Resource.Id.empName);
        email = (EditText)FindViewById(Resource.Id.empEmail);
        phone = (EditText)FindViewById(Resource.Id.empPhone);
        designation = (EditText)FindViewById(Resource.Id.empDesignation);
        submitBtn = (Button)FindViewById(Resource.Id.insertEmpBtn);
    }
}}

更新2

Bellow是update employee

的代码

namespace AppwithDB.Resources
{
[Activity(Label = "updateEmployee")]
class updateEmployee:Activity
{
    ListView list; 
    EditText dName, dEmail, dPhone, dDesignation;
    String name, email, phone, designation;
    SQLiteHelper dbHelper;
    int click_Employee;
    Button upBtn;

    protected override void OnCreate(Bundle bundle)
    {
        base.OnCreate(bundle);

        // Create your application here
        SetContentView(Resource.Layout.update);
        initialize();
        dbHelper = new SQLiteHelper(this);
        System.Collections.ArrayList dataList = dbHelper.getALLEmployeesData();
        string[] myArr = (string[])dataList.ToArray(typeof(string));
        list.Adapter = new ArrayAdapter(this, Android.Resource.Layout.SimpleExpandableListItem1, myArr);

        list.ItemClick += List_ItemClick;

        upBtn.Click += delegate
        {
            dbHelper.updateEmployeeInfo(click_Employee, dName.Text.ToString(), dEmail.Text.ToString(), dPhone.Text.ToString(), dDesignation.Text.ToString());
        };

    }

    private void initialize()
    {
        list = (ListView)FindViewById(Resource.Id.listView1);
        dName = (EditText)FindViewById(Resource.Id.eName);
        dEmail = (EditText)FindViewById(Resource.Id.eEmail);
        dPhone = (EditText)FindViewById(Resource.Id.ePhone);
        dDesignation = (EditText)FindViewById(Resource.Id.eDesignation);
        upBtn = (Button)FindViewById(Resource.Id.updateEmploy);
    }
    void List_ItemClick(object sender, AdapterView.ItemClickEventArgs e)
    {
        click_Employee = e.Position + 1;
        ICursor c = dbHelper.getSingleEntry(click_Employee);
        c.MoveToFirst();
        name = c.GetString(c.GetColumnIndex(dbHelper.EMPLOYEE_NAME));
        email = c.GetString(c.GetColumnIndex(dbHelper.EMPLOYEE_EMAIL));
        phone = c.GetString(c.GetColumnIndex(dbHelper.EMPLOYEE_PHONE));
        designation = c.GetString(c.GetColumnIndex(dbHelper.EMPLOYEE_DESIGNATION));
        dName.Text = name;
        dEmail.Text = email;
        dPhone.Text = phone;
        dDesignation.Text = designation;
    }


}}

更新3：

Bellow是xmls和complete_data

的update

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:padding="10dp">
<ScrollView
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">
        <ListView
            android:id="@+id/listView1"
            android:layout_width="match_parent"
            android:layout_height="350dp"
            android:divider="#000"
            android:dividerHeight="1dp" />
        <TextView
            android:id="@+id/eName"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Name" />
        <TextView
            android:id="@+id/eEmail"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Email" />
        <TextView
            android:id="@+id/ePhone"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Phone" />
        <TextView
            android:id="@+id/eDesignation"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Designation" />
    </LinearLayout></ScrollView></LinearLayout>

更新xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:padding="10dp">
<ScrollView
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">
        <ListView
            android:id="@+id/listView1"
            android:layout_width="match_parent"
            android:layout_height="250dp"
            android:divider="#000"
            android:dividerHeight="1dp" />
        <EditText
            android:id="@+id/upName"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:hint="Name" />
        <EditText
            android:id="@+id/upEmail"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:hint="Email" />
        <EditText
            android:id="@+id/upPhone"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:hint="Phone" />
        <EditText
            android:id="@+id/upDesignation"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:hint="Designation" />
        <Button
            android:id="@+id/updateEmploy"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:text="Update Employee" />
    </LinearLayout></ScrollView></LinearLayout>

为了更好地理解，上面给出了示例代码。

任何帮助都将受到高度赞赏

Answer 1

问题是您使用了错误的View ID。您的XML中有upName，您正在搜索Resource.Id.eName 要解决问题，您需要将Resource.Id.eName更改为Resource.Id.upName

Xamarin android无法分配文本值来编辑文本

1 个答案: