在xamarin应用程序中没有写任何内容时，如何填写缺失条目?

Question

我正在做导入页面，如果用户留下一些空白条目并单击导入按钮，我想用缺失填充空白条目。我试过这样做:

if (liveryEntry.Text == null)
{
liveryEntry.Text = "Missing";
}
if (registrationEntry.Text == null)
{
registrationEntry.Text = "Missing";
}
if (airportEntry == null)
{
airportEntry.Text = "Missing";
}                
if (commentEntry == null)
{
commentEntry.Text = "Missing";
}

但有时它有效，用思念填满它，有时它不起作用。这是怎么回事，还是有别的办法?下面是方法的完整代码:

private async void buttonImport_Clicked(object sender, EventArgs e)
{
var db = new SQLiteConnection(_dbPath);
db.CreateTable<Airplane>();
collectionPlane.IsVisible = false;
collectionAirline.IsVisible = false;
collectionLivery.IsVisible = false;
collectionRegistration.IsVisible = false;
collectionAirport.IsVisible = false;
try
{
if (liveryEntry.Text == null)
{
liveryEntry.Text = "Missing";
}
if (registrationEntry.Text == null)
{
registrationEntry.Text = "Missing";
}
if (airportEntry == null)
{
airportEntry.Text = "Missing";
}                
if (commentEntry == null)
{
commentEntry.Text = "Missing";
}
if (planeEntry.Text != null && airlineEntry.Text != null)
{
var url = PhotoPick();
int i = 1;
int same = 0;
string fileName = registrationEntry.Text;
for (int b = 1; b <= GetNumberPhotos(); b++)
{
if (db.Table<Airplane>().FirstOrDefault(d => d.Id == b) != null)
{
var rowData = db.Table<Airplane>().FirstOrDefault(d => d.Id == b);
string match = rowData.Registration;
if (fileName == match)
{
same++;
}
}
}
i = 1 + same;
fileName = registrationEntry.Text + "-" + i;
var thumbUrl = CreateThumbnail(await url, fileName);
var maxPK = db.Table<Airplane>().OrderByDescending(c => c.Id).FirstOrDefault();
Airplane airplane = new Airplane()
{
Id = (maxPK == null ? 1 : maxPK.Id + 1),
SearchId = planeEntry.Text + airlineEntry.Text + liveryEntry.Text + registrationEntry.Text + airportEntry.Text + datePicker.Date.ToString() + commentEntry.Text,
Plane = planeEntry.Text.ToUpper(),
Airline = airlineEntry.Text,
Livery = liveryEntry.Text,
Registration = registrationEntry.Text.ToUpper(),
Airport = airportEntry.Text.ToUpper(),
Date = datePicker.Date,
Comment = commentEntry.Text,
Url = await url,
ThumbnailUrl = thumbUrl
};
db.Insert(airplane);
await DisplayAlert("Saved", planeEntry.Text + " of " + airlineEntry.Text + " is saved.", "OK");
planeEntry.Text = "";
airlineEntry.Text = "";
liveryEntry.Text = "";
registrationEntry.Text = "";
airportEntry.Text = "";                    
commentEntry.Text = "";
}
else
await DisplayAlert("Fill all needed fields", "You have to fill all fields except livery and comment", "OK");
}
catch
{
await DisplayAlert("Error", "Something went wrong", "Try again");
}
}

Answer 1

这可能是某种错误或误解@Cfun已经解决了if ( string.IsNullOrEmpty(liveryEntry.Text))和它的工作如预期。