我的問題是如果我只需要呼叫我的方法一次，如何在進度條上顯示進度？我正在 WPF 中處理 MVVM 專案。我必須在進度條上顯示我的回圈進度。如果我在 Model 類中有類似的東西，我的 ProgressBar 會正確更新，但只有一次
public double progressBarValue;
public string inputText;
public int quantityOfNumbers
{
get;
set;
}
public void inputTextToInt(string inputText)
{
progressBarValue = Convert.ToInt32(inputText);
quantityOfNumbers = Convert.ToInt32(inputText);
//work();
}
但是，如果我嘗試使用以下代碼實時更新我的??進度條：
public void inputTextToInt(string inputText)
{
//progressBarValue = Convert.ToInt32(inputText);
quantityOfNumbers = Convert.ToInt32(inputText);
work();
}
private async void work()
{
RandNumbers randNumbers = new RandNumbers(quantityOfNumbers);
var progress = new Progress<double>(value =>
{
progressBarValue = value;
Console.WriteLine(progressBarValue);
});
await Task.Run(() => randNumbers.RandAllNumbers(progress));
}
我的 ProgressBar 沒有任何進展。我已經檢查了控制臺，在這一行中我的 progressBarValue 正在正確更改但它沒有發送到我的 ViewModel 類。
progressBarValue = value;
這是我的 ViewModel 類：
private ModelTME_App model = new ModelTME_App();
public string inputText
{
get { return model.inputText; }
set { model.inputText = value;
onPropertyChanged(nameof(inputText));
}
}
public double progressBarValue
{
get {
Console.WriteLine(model.progressBarValue);
return model.progressBarValue;
}
}
private ICommand inputTextToInt = null;
public ICommand InputTextToInt
{
get
{
if(inputTextToInt == null)
{
inputTextToInt = new RelayCommand(
(object o) =>
{
model.inputTextToInt(inputText);
onPropertyChanged(nameof(progressBarValue));
},
(object o) =>
{
return model.progressBarValue == 0;
});
}
return inputTextToInt;
}
}
public event PropertyChangedEventHandler PropertyChanged;
private void onPropertyChanged(string nameOfProperty)
{
if(PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(nameOfProperty));
}
}
}
我的 RelayCommandClass
public class RelayCommand : ICommand
{
private Action<object> execute;
private Func<object, bool> canExecute;
public RelayCommand(Action<object> execute, Func<object, bool> canExecute = null)
{
if (execute == null)
{
throw new ArgumentNullException(nameof(execute));
}
else
{
this.execute = execute;
}
this.canExecute = canExecute;
}
public event EventHandler CanExecuteChanged
{
add
{
CommandManager.RequerySuggested = value;
}
remove
{
CommandManager.RequerySuggested -= value;
}
}
public bool CanExecute(object parameter)
{
if(canExecute == null)
{
return true;
}
else
{
return canExecute(parameter);
}
}
public void Execute(object parameter)
{
execute(parameter);
}
}
uj5u.com熱心網友回復：
Binding.Source必須始終引發事件INotifyPropertyChanged.PropertyChanged以觸發Binding更新更新Binding.Target。
您應該避免通過委托屬性系結到模型。模型不應公開 API 以允許這樣做（資料隱藏）。
正確的模式是ProgressChanged在模型中實作視圖模型可以觀察到的事件。
還要避免一些代碼異味：
void永遠不要從方法回傳，async除非該方法是事件處理程式。方法async必須回傳Taskor 。Task<T>回傳的Task必須在呼叫鏈上傳播并等待。避免在 lambda 中捕獲成員變數。在某些情況下，這可能會造成記憶體泄漏
使用方法將值從View Model傳遞到Model 。將所有模型屬性暴露給視圖模型會暴露太多資訊細節（例如設定哪些屬性以將模型更改為有效狀態）。而是讓公共方法請求所需的資料作為引數或引數物件。屬性應該是私有的（配置物件所需的屬性除外）。
使用成員和引數名稱，例如
ProgressBar...orInputText...會暗示您的模型設計不正確。由于模型不知道視圖，因此它對進度條或輸入文本也不感興趣。可能是簡單的命名問題或嚴重的設計問題。您應該嘗試實施官方的 C#命名指南
Model.cs
事件ProgressChanged是使用ProgressChangedEventArgs.
class Model
{
public event EventHandler<ProgressChangedEventArgs> ProgressChanged;
private double ProgressPercentage { get; set; }
private string NumericText { get; set; }
private int QuantityOfNumbers { get; set; }
protected virtual void OnProgressCHanged(double percentage)
=> this.ProgressChanged?.Invoke(new ProgressChangedEventArgs(percentage, string.Empty);
public async Task<int> ToIntAsync(string numericText)
{
NumericText = numericText;
QuantityOfNumbers = Convert.ToInt32(NumericText);
await WorkAsync();
return QuantityOfNumbers;
}
private async Task WorkAsync()
{
// Can you guarantee that this method is called from the UI thread?
var progress = new Progress<double>(value =>
{
ProgressPercentage = value;
Console.WriteLine(ProgressBarValue);
OnProgressChanged(ProgressBarValue);
});
// Avoid capturing member variables in lambdas
int quantityOfNumbers = QuantityOfNumbers;
await Task.Run(() =>
{
var randNumbers = new RandNumbers(quantityOfNumbers);
randNumbers.RandAllNumbers(progress));
});
}
}
視圖模型.cs
class ViewModel : INotifyPropertyChanged
{
private Model _model;
// TODO::Let property raise PropertyChanged event
public double ProgressValue { get; set; }
public ICommand InputTextToIntCommand => new RelayCommand(ExecuteInputTextToIntCommandAsync);
// TODO::Let property raise PropertyChanged event
public string NumericText { get; set;}
public ViewModel()
{
_model = new Model();
}
// Make sure RelayCommand can execute async delegates
private async Task ExecuteInputTextToIntCommandAsync()
{
_model.PropgressChnaged = OnProgressChanged;
// Pass value to model
var quantityOfNumbersResult = await _model.ToIntAsync(this.NumericText);
}
private void OnProgressChanged(object sender, ProgressChangedEventArgs e)
{
this.ProgressValue = e.ProgressPercentage;
if (this.ProgressValue >= 100)
{
_model.PropgressChnaged -= OnProgressChanged;
}
}
}
一個允許取消的簡單異步命令實作（基于發布的示例）：
public class RelayCommand : ICommand
{
private CancellationTokenSource cancellationTokenSource;
private readonly Func<object, Task> executeAsync;
private readonly Func<object, CancellationToken, Task> executeCancellableAsync;
private Action<object> execute;
private Func<object, bool> canExecute;
public RelayCommand(Func<object, CancellationToken, Task> executeCancellableAsync, Func<object, bool> canExecute)
{
this.executeCancellableAsync = executeCancellableAsync;
this.canExecute = canExecute;
}
public RelayCommand(Func<object, Task> executeAsync, Func<object, bool> canExecute)
{
this.executeAsync = executeAsync;
this.canExecute = canExecute;
}
public RelayCommand(Action<object> execute, Func<object, bool> canExecute = null)
{
if (execute == null)
{
throw new ArgumentNullException(nameof(execute));
}
this.execute = execute;
this.canExecute = canExecute;
}
public event EventHandler CanExecuteChanged
{
add
{
CommandManager.RequerySuggested = value;
}
remove
{
CommandManager.RequerySuggested -= value;
}
}
public bool CanExecute(object parameter)
{
return canExecute?.Invoke(parameter) ?? true;
}
public void Execute(object parameter)
{
_ = ExecuteAsync(parameter);
}
public async Task ExecuteAsync(object commandParameter)
{
using (this.cancellationTokenSource = new CancellationTokenSource())
{
await ExecuteAsync(commandParameter, this.cancellationTokenSource.Token);
}
}
public Task ExecuteAsync(object commandParameter, CancellationToken cancellationToken)
{
if (this.executeCancellableAsync is not null)
{
return this.executeCancellableAsync.Invoke(commandParameter, cancellationToken);
}
else if (this.executeAsync is not null)
{
return this.executeAsync.Invoke(commandParameter);
}
else
{
this.execute.Invoke(commandParameter);
return Task.CompletedTask;
}
}
public void Cancel()
{
this.cancellationTokenSource?.Cancel();
}
}
uj5u.com熱心網友回復：
要在回圈中實時更新進度條：
public double progressBarValue;
progressBarValue = 0;
int len = array.Length;
for(int i=0; i<len; i ) {
//do something
//for end of every iteration
progressBarValue = (double)i / len * 100;
work();
}
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