Events in Blazor Dropdown Tree Component

19 Feb 202519 minutes to read

The Blazor Dropdown Tree component has a list of events that can be triggered for certain actions.

Created

The Blazor Dropdown Tree component’s Created event is triggered once the Dropdown Tree has been successfully created

@using Syncfusion.Blazor.Navigations

<SfDropDownTree TItem="EmployeeData" TValue="string" Placeholder="Select an employee" Width="500px" Created="OnCreated">
    <DropDownTreeField TItem="EmployeeData" DataSource="Data" ID="Id" Text="Name" HasChildren="HasChild" ParentID="PId"></DropDownTreeField>
</SfDropDownTree>

@code {
    List<EmployeeData> Data = new List<EmployeeData>
    {
        new EmployeeData() { Id = "1", Name = "Steven Buchanan", Job = "General Manager", HasChild = true, Expanded = true },
        new EmployeeData() { Id = "2", PId = "1", Name = "Laura Callahan", Job = "Product Manager", HasChild = true },
        new EmployeeData() { Id = "3", PId = "2", Name = "Andrew Fuller", Job = "Team Lead", HasChild = true },
        new EmployeeData() { Id = "4", PId = "3", Name = "Anne Dodsworth", Job = "Developer" },
        new EmployeeData() { Id = "10", PId = "3", Name = "Lilly", Job = "Developer" },
        new EmployeeData() { Id = "5", PId = "1", Name = "Nancy Davolio", Job = "Product Manager", HasChild = true },
        new EmployeeData() { Id = "6", PId = "5", Name = "Michael Suyama", Job = "Team Lead", HasChild = true },
        new EmployeeData() { Id = "7", PId = "6", Name = "Robert King", Job = "Developer" },
        new EmployeeData() { Id = "11", PId = "6", Name = "Mary", Job = "Developer" },
        new EmployeeData() { Id = "9", PId = "1", Name = "Janet Leverling", Job = "HR"}
    };

    void OnCreated()
    {
        // Here, you can customize your code.
    }

    class EmployeeData
    {
        public string? Id { get; set; }
        public string? Name { get; set; }
        public string? Job { get; set; }
        public bool HasChild { get; set; }
        public bool Expanded { get; set; }
        public string? PId { get; set; }
    }
}

Destroyed

The Blazor Dropdown Tree’s Destroyed event is triggered when the Dropdown Tree component is completely destroyed, allowing you to confirm its destruction.

@using Syncfusion.Blazor.Navigations

<SfDropDownTree TItem="EmployeeData" TValue="string" Placeholder="Select an employee" Width="500px" Destroyed="DestroyHandler">
    <DropDownTreeField TItem="EmployeeData" DataSource="Data" ID="Id" Text="Name" HasChildren="HasChild" ParentID="PId"></DropDownTreeField>
</SfDropDownTree>

@code {
    List<EmployeeData> Data = new List<EmployeeData>
    {
        new EmployeeData() { Id = "1", Name = "Steven Buchanan", Job = "General Manager", HasChild = true, Expanded = true },
        new EmployeeData() { Id = "2", PId = "1", Name = "Laura Callahan", Job = "Product Manager", HasChild = true },
        new EmployeeData() { Id = "3", PId = "2", Name = "Andrew Fuller", Job = "Team Lead", HasChild = true },
        new EmployeeData() { Id = "4", PId = "3", Name = "Anne Dodsworth", Job = "Developer" },
        new EmployeeData() { Id = "10", PId = "3", Name = "Lilly", Job = "Developer" },
        new EmployeeData() { Id = "5", PId = "1", Name = "Nancy Davolio", Job = "Product Manager", HasChild = true },
        new EmployeeData() { Id = "6", PId = "5", Name = "Michael Suyama", Job = "Team Lead", HasChild = true },
        new EmployeeData() { Id = "7", PId = "6", Name = "Robert King", Job = "Developer" },
        new EmployeeData() { Id = "11", PId = "6", Name = "Mary", Job = "Developer" },
        new EmployeeData() { Id = "9", PId = "1", Name = "Janet Leverling", Job = "HR"}
    };

    void DestroyHandler()
    {
        // Here, you can customize your code.
    }

    class EmployeeData
    {
        public string? Id { get; set; }
        public string? Name { get; set; }
        public string? Job { get; set; }
        public bool HasChild { get; set; }
        public bool Expanded { get; set; }
        public string? PId { get; set; }
    }
}

OnPopupOpen

The Blazor Dropdown Tree OnPopupOpen event is triggered whenever a Dropdown Tree popup is opened after animation.

@using Syncfusion.Blazor.Navigations
@using Syncfusion.Blazor.DropDowns

<SfDropDownTree TItem="EmployeeData" TValue="string" Placeholder="Select an employee" Width="500px" OnPopupOpen="OnPopupOpen">
    <DropDownTreeField TItem="EmployeeData" DataSource="Data" ID="Id" Text="Name" HasChildren="HasChild" ParentID="PId"></DropDownTreeField>
</SfDropDownTree>

@code {
    List<EmployeeData> Data = new List<EmployeeData>
    {
        new EmployeeData() { Id = "1", Name = "Steven Buchanan", Job = "General Manager", HasChild = true, Expanded = true },
        new EmployeeData() { Id = "2", PId = "1", Name = "Laura Callahan", Job = "Product Manager", HasChild = true },
        new EmployeeData() { Id = "3", PId = "2", Name = "Andrew Fuller", Job = "Team Lead", HasChild = true },
        new EmployeeData() { Id = "4", PId = "3", Name = "Anne Dodsworth", Job = "Developer" },
        new EmployeeData() { Id = "10", PId = "3", Name = "Lilly", Job = "Developer" },
        new EmployeeData() { Id = "5", PId = "1", Name = "Nancy Davolio", Job = "Product Manager", HasChild = true },
        new EmployeeData() { Id = "6", PId = "5", Name = "Michael Suyama", Job = "Team Lead", HasChild = true },
        new EmployeeData() { Id = "7", PId = "6", Name = "Robert King", Job = "Developer" },
        new EmployeeData() { Id = "11", PId = "6", Name = "Mary", Job = "Developer" },
        new EmployeeData() { Id = "9", PId = "1", Name = "Janet Leverling", Job = "HR"}
    };

    void OnPopupOpen(PopupEventArgs args)
    {
        // Here, you can customize your code.
    }

    class EmployeeData
    {
        public string? Id { get; set; }
        public string? Name { get; set; }
        public string? Job { get; set; }
        public bool HasChild { get; set; }
        public bool Expanded { get; set; }
        public string? PId { get; set; }
    }
}

OnPopupClose

The Blazor Dropdown Tree OnPopupClose event is triggered before a Dropdown Tree popup is closed after animation.

@using Syncfusion.Blazor.Navigations
@using Syncfusion.Blazor.DropDowns

<SfDropDownTree TItem="EmployeeData" TValue="string" Placeholder="Select an employee" Width="500px" OnPopupClose="OnPopupClose">
    <DropDownTreeField TItem="EmployeeData" DataSource="Data" ID="Id" Text="Name" HasChildren="HasChild" ParentID="PId"></DropDownTreeField>
</SfDropDownTree>

@code {
    List<EmployeeData> Data = new List<EmployeeData>
    {
        new EmployeeData() { Id = "1", Name = "Steven Buchanan", Job = "General Manager", HasChild = true, Expanded = true },
        new EmployeeData() { Id = "2", PId = "1", Name = "Laura Callahan", Job = "Product Manager", HasChild = true },
        new EmployeeData() { Id = "3", PId = "2", Name = "Andrew Fuller", Job = "Team Lead", HasChild = true },
        new EmployeeData() { Id = "4", PId = "3", Name = "Anne Dodsworth", Job = "Developer" },
        new EmployeeData() { Id = "10", PId = "3", Name = "Lilly", Job = "Developer" },
        new EmployeeData() { Id = "5", PId = "1", Name = "Nancy Davolio", Job = "Product Manager", HasChild = true },
        new EmployeeData() { Id = "6", PId = "5", Name = "Michael Suyama", Job = "Team Lead", HasChild = true },
        new EmployeeData() { Id = "7", PId = "6", Name = "Robert King", Job = "Developer" },
        new EmployeeData() { Id = "11", PId = "6", Name = "Mary", Job = "Developer" },
        new EmployeeData() { Id = "9", PId = "1", Name = "Janet Leverling", Job = "HR"}
    };

    void OnPopupClose(PopupEventArgs args)
    {
        // Here, you can customize your code.
    }

    class EmployeeData
    {
        public string? Id { get; set; }
        public string? Name { get; set; }
        public string? Job { get; set; }
        public bool HasChild { get; set; }
        public bool Expanded { get; set; }
        public string? PId { get; set; }
    }
}

ValueChanging

The Blazor Dropdown Tree component’s ValueChanging event is triggered when an item in a popup is selected or when the model value is changed by user.

@using Syncfusion.Blazor.Popups
@using Syncfusion.Blazor.Buttons
@using Syncfusion.Blazor.Navigations

<div>
    <SfDropDownTree TItem="EmployeeData" TValue="string" Placeholder="Select an employee" Width="500px" ValueChanging="ValueChanged">
        <DropDownTreeField TItem="EmployeeData" DataSource="Data" ID="Id" Text="Name" HasChildren="HasChild" ParentID="PId"></DropDownTreeField>
    </SfDropDownTree>
</div>
<SfDialog Width="335px" IsModal="true" @bind-Visible="Visibility">
    <DialogTemplates>
        <Header>Employee Details</Header>
        <Content>
            <p class="employee">Name - @Name</p>
            <p class="employee">Role - @Role</p>
        </Content>
    </DialogTemplates>
    <DialogButtons>
        <DialogButton Content="OK" IsPrimary="true" OnClick="@DlgButtonClick" />
    </DialogButtons>
</SfDialog>

<style>
    .employee {
        font-size: 18px;
        margin-top: 10%;
        margin-left: 20%;
        font-weight: 500;
    }
</style>

@code {
    private string Name { get; set; } = string.Empty;
    private string Role { get; set; } = string.Empty;
    private bool Visibility { get; set; }

    private void DlgButtonClick()
    {
        this.Visibility = false;
    }

    List<EmployeeData> Data = new List<EmployeeData>
    {
        new EmployeeData() { Id = "1", Name = "Steven Buchanan", Job = "General Manager", HasChild = true, Expanded = true },
        new EmployeeData() { Id = "2", PId = "1", Name = "Laura Callahan", Job = "Product Manager", HasChild = true },
        new EmployeeData() { Id = "3", PId = "2", Name = "Andrew Fuller", Job = "Team Lead", HasChild = true },
        new EmployeeData() { Id = "4", PId = "3", Name = "Anne Dodsworth", Job = "Developer" },
        new EmployeeData() { Id = "10", PId = "3", Name = "Lilly", Job = "Developer" },
        new EmployeeData() { Id = "5", PId = "1", Name = "Nancy Davolio", Job = "Product Manager", HasChild = true },
        new EmployeeData() { Id = "6", PId = "5", Name = "Michael Suyama", Job = "Team Lead", HasChild = true },
        new EmployeeData() { Id = "7", PId = "6", Name = "Robert King", Job = "Developer" },
        new EmployeeData() { Id = "11", PId = "6", Name = "Mary", Job = "Developer" },
        new EmployeeData() { Id = "9", PId = "1", Name = "Janet Leverling", Job = "HR"}
    };

    void ValueChanged(DdtChangeEventArgs<string> args)
    {
        EmployeeData currentData = Data?.Find((item) => item.Id == args.NodeData.Id);
        Name = currentData?.Name;
        Role = currentData?.Job;
        this.Visibility = true;
    }

    class EmployeeData
    {
        public string? Id { get; set; }
        public string? Name { get; set; }
        public string? Job { get; set; }
        public bool HasChild { get; set; }
        public bool Expanded { get; set; }
        public string? PId { get; set; }
    }
}

ValueChanged

The Blazor Dropdown Tree component’s ValueChanged event is triggered when the value changed in the Dropdown Tree component.

@using Syncfusion.Blazor.Navigations

<SfDropDownTree TItem="EmployeeData" TValue="string" Placeholder="Select an employee" Width="500px" ValueChanged="ValueChanged">
    <DropDownTreeField TItem="EmployeeData" DataSource="Data" ID="Id" Text="Name" HasChildren="HasChild" ParentID="PId"></DropDownTreeField>
</SfDropDownTree>

@code {
    List<EmployeeData> Data = new List<EmployeeData>
    {
        new EmployeeData() { Id = "1", Name = "Steven Buchanan", Job = "General Manager", HasChild = true, Expanded = true },
        new EmployeeData() { Id = "2", PId = "1", Name = "Laura Callahan", Job = "Product Manager", HasChild = true },
        new EmployeeData() { Id = "3", PId = "2", Name = "Andrew Fuller", Job = "Team Lead", HasChild = true },
        new EmployeeData() { Id = "4", PId = "3", Name = "Anne Dodsworth", Job = "Developer" },
        new EmployeeData() { Id = "10", PId = "3", Name = "Lilly", Job = "Developer" },
        new EmployeeData() { Id = "5", PId = "1", Name = "Nancy Davolio", Job = "Product Manager", HasChild = true },
        new EmployeeData() { Id = "6", PId = "5", Name = "Michael Suyama", Job = "Team Lead", HasChild = true },
        new EmployeeData() { Id = "7", PId = "6", Name = "Robert King", Job = "Developer" },
        new EmployeeData() { Id = "11", PId = "6", Name = "Mary", Job = "Developer" },
        new EmployeeData() { Id = "9", PId = "1", Name = "Janet Leverling", Job = "HR"}
    };

    void ValueChanged(List<string> args)
    {
        // Here, you can customize your code.
    }

    class EmployeeData
    {
        public string? Id { get; set; }
        public string? Name { get; set; }
        public string? Job { get; set; }
        public bool HasChild { get; set; }
        public bool Expanded { get; set; }
        public string? PId { get; set; }
    }
}

Filtering

The Blazor Dropdown Tree component’s Filtering event is triggered when user types a text in search box.

@using Syncfusion.Blazor.Navigations

<SfDropDownTree TItem="EmployeeData" TValue="string" Placeholder="Select an employee" Width="500px" AllowFiltering="true" Filtering="OnFiltering">
    <DropDownTreeField TItem="EmployeeData" DataSource="Data" ID="Id" Text="Name" HasChildren="HasChild" ParentID="PId"></DropDownTreeField>
</SfDropDownTree>

@code {
    List<EmployeeData> Data = new List<EmployeeData>
    {
        new EmployeeData() { Id = "1", Name = "Steven Buchanan", Job = "General Manager", HasChild = true, Expanded = true },
        new EmployeeData() { Id = "2", PId = "1", Name = "Laura Callahan", Job = "Product Manager", HasChild = true },
        new EmployeeData() { Id = "3", PId = "2", Name = "Andrew Fuller", Job = "Team Lead", HasChild = true },
        new EmployeeData() { Id = "4", PId = "3", Name = "Anne Dodsworth", Job = "Developer" },
        new EmployeeData() { Id = "10", PId = "3", Name = "Lilly", Job = "Developer" },
        new EmployeeData() { Id = "5", PId = "1", Name = "Nancy Davolio", Job = "Product Manager", HasChild = true },
        new EmployeeData() { Id = "6", PId = "5", Name = "Michael Suyama", Job = "Team Lead", HasChild = true },
        new EmployeeData() { Id = "7", PId = "6", Name = "Robert King", Job = "Developer" },
        new EmployeeData() { Id = "11", PId = "6", Name = "Mary", Job = "Developer" },
        new EmployeeData() { Id = "9", PId = "1", Name = "Janet Leverling", Job = "HR"}
    };

    void OnFiltering(DdtFilteringEventArgs args)
    {
        // Here, you can customize your code.
    }

    class EmployeeData
    {
        public string? Id { get; set; }
        public string? Name { get; set; }
        public string? Job { get; set; }
        public bool HasChild { get; set; }
        public bool Expanded { get; set; }
        public string? PId { get; set; }
    }
}

OnActionFailure

The Blazor Dropdown Tree component’s OnActionFailure event is triggered when any Dropdown Tree action fails to produce the desired outcome. By utilizing this event, one can obtain information about the error and its root cause. In the sample provided, an incorrect URL has been given, causing the OnActionFailure event to be thrown.

@using Syncfusion.Blazor.Navigations
@using Syncfusion.Blazor.Data

<SfDropDownTree TValue="int?" TItem="TreeData" ID="remote" Placeholder="Select a name" Width="500px" OnActionFailure="OnActionFailureTemplate">
    <ChildContent>
        <DropDownTreeField TItem="TreeData" Query="@employeeQuery" ID="EmployeeID" Text="FirstName" HasChildren="EmployeeID">
            <SfDataManager Url="https://services.odata.org/V4/Northwind/Northwind.svc" Adaptor="Syncfusion.Blazor.Adaptors.ODataV4Adaptor" CrossDomain="true"></SfDataManager>
        </DropDownTreeField>
        <DropDownTreeField TItem="TreeData" Query="@orderQuery" Id="OrderID" Text="ShipName" ParentID="EmployeeID">
            <SfDataManager Url="https://services.odata.org/V4/Northwind/Northwind.svs" Adaptor="Syncfusion.Blazor.Adaptors.ODataV4Adaptor" CrossDomain="true"></SfDataManager>
        </DropDownTreeField>
    </ChildContent>
    <ActionFailureTemplate>
        <span>A request to fetch data is failed.</span>
    </ActionFailureTemplate>
</SfDropDownTree>

@code {
    List<string> EmployeeDetails { get; set; } = new List<string>() { "EmployeeID", "FirstName", "Title" };
    List<string> OrderDetails { get; set; } = new List<string>() { "OrderID", "EmployeeID", "ShipName" };
    Query? employeeQuery;
    Query? orderQuery;

    protected override void OnInitialized()
    {
        base.OnInitialized();
        employeeQuery = new Query().From("Employees").Select(EmployeeDetails).Take(5);
        orderQuery = new Query().From("Orders").Select(OrderDetails).Take(5);
    }

    void OnActionFailureTemplate()
    {

    }
    class TreeData
    {
        public int? EmployeeID { get; set; }
        public int OrderID { get; set; }
        public string? ShipName { get; set; }
        public string? FirstName { get; set; }
    }
}