c# - How to access the browsers localStorage in Blazor?

C# - How to access the browsers localStorage in Blazor?

Accessing the browser's localStorage in a Blazor application involves interfacing with JavaScript from C# code. Blazor allows you to call JavaScript functions from C# and vice versa using JavaScript Interoperability (JS Interop).

Here's a step-by-step guide on how to access and manipulate the browser's localStorage in a Blazor application:

1. Define JavaScript Functions

First, you need to define JavaScript functions for interacting with localStorage. These functions will be called from Blazor.

Create a JavaScript file, e.g., localStorage.js, and include it in your Blazor application.

localStorage.js

// Set an item in localStorage function setLocalStorageItem(key, value) { localStorage.setItem(key, value); } // Get an item from localStorage function getLocalStorageItem(key) { return localStorage.getItem(key); } // Remove an item from localStorage function removeLocalStorageItem(key) { localStorage.removeItem(key); }

Include this JavaScript file in your _Host.cshtml (Blazor Server) or index.html (Blazor WebAssembly).

_Host.cshtml (Blazor Server)

<!DOCTYPE html> <html> <head> <!-- Other head content --> <script src="localStorage.js"></script> </head> <body> <app>Loading...</app> <script src="_framework/blazor.server.js"></script> </body> </html>

index.html (Blazor WebAssembly)

<!DOCTYPE html> <html> <head> <!-- Other head content --> <script src="localStorage.js"></script> </head> <body> <app>Loading...</app> <script src="_framework/blazor.webassembly.js"></script> </body> </html>

2. Create JavaScript Interop Methods

In your Blazor component or service, use JS Interop to call the JavaScript functions.

ExampleComponent.razor

@page "/example" @inject IJSRuntime JSRuntime <h3>LocalStorage Example</h3> <button @onclick="SaveItem">Save Item</button> <button @onclick="LoadItem">Load Item</button> <button @onclick="RemoveItem">Remove Item</button> <p>@message</p> @code { private string message; private async Task SaveItem() { await JSRuntime.InvokeVoidAsync("setLocalStorageItem", "myKey", "myValue"); message = "Item saved!"; } private async Task LoadItem() { var value = await JSRuntime.InvokeAsync<string>("getLocalStorageItem", "myKey"); message = $"Loaded item: {value}"; } private async Task RemoveItem() { await JSRuntime.InvokeVoidAsync("removeLocalStorageItem", "myKey"); message = "Item removed!"; } }

3. Handle Data Types

If you need to store and retrieve more complex data types (like objects), you should serialize them to/from JSON. You can use System.Text.Json.JsonSerializer or Newtonsoft.Json for serialization/deserialization in Blazor.

JavaScript Example for JSON

In localStorage.js:

// Set a JSON object in localStorage function setLocalStorageObject(key, obj) { localStorage.setItem(key, JSON.stringify(obj)); } // Get a JSON object from localStorage function getLocalStorageObject(key) { return JSON.parse(localStorage.getItem(key)); }

In your Blazor component:

@page "/example" @inject IJSRuntime JSRuntime <button @onclick="SaveObject">Save Object</button> <button @onclick="LoadObject">Load Object</button> <p>@message</p> @code { private string message; private async Task SaveObject() { var myObject = new { Name = "John", Age = 30 }; await JSRuntime.InvokeVoidAsync("setLocalStorageObject", "myObjectKey", myObject); message = "Object saved!"; } private async Task LoadObject() { var myObject = await JSRuntime.InvokeAsync<JsonElement>("getLocalStorageObject", "myObjectKey"); var name = myObject.GetProperty("Name").GetString(); var age = myObject.GetProperty("Age").GetInt32(); message = $"Loaded object: Name={name}, Age={age}"; } }

Summary

  1. Define JavaScript Functions: Create functions for accessing and manipulating localStorage in a .js file.
  2. Include JavaScript File: Include this file in your Blazor project.
  3. Use JS Interop: Call these JavaScript functions from your Blazor components or services using IJSRuntime.
  4. Handle Serialization: For complex data types, use JSON serialization and deserialization.

By following these steps, you can efficiently interact with the browser's localStorage from a Blazor application.

Examples

  1. "How to read localStorage in Blazor WebAssembly?"

    • Description: This query involves accessing localStorage in a Blazor WebAssembly application.
    • Code:
      @page "/localstorage" @inject IJSRuntime JSRuntime <h3>LocalStorage Example</h3> <button @onclick="ReadLocalStorage">Read LocalStorage</button> <p>@localStorageValue</p> @code { private string localStorageValue; private async Task ReadLocalStorage() { localStorageValue = await JSRuntime.InvokeAsync<string>("localStorage.getItem", "myKey"); } }
      • Explanation: This code uses JavaScript interop (IJSRuntime) to read a value from localStorage and display it in a Blazor WebAssembly component.

  2. "How to write to localStorage from Blazor WebAssembly?"

    • Description: This query focuses on writing data to localStorage from a Blazor WebAssembly app.
    • Code:
      @page "/localstorage" @inject IJSRuntime JSRuntime <h3>LocalStorage Example</h3> <input @bind="inputValue" placeholder="Enter value" /> <button @onclick="WriteLocalStorage">Save to LocalStorage</button> @code { private string inputValue; private async Task WriteLocalStorage() { await JSRuntime.InvokeVoidAsync("localStorage.setItem", "myKey", inputValue); } }
      • Explanation: This code uses IJSRuntime to write a value to localStorage when a button is clicked.

  3. "How to remove an item from localStorage in Blazor?"

    • Description: This query deals with removing an item from localStorage in a Blazor application.
    • Code:
      @page "/localstorage" @inject IJSRuntime JSRuntime <h3>LocalStorage Example</h3> <button @onclick="RemoveFromLocalStorage">Remove Item</button> @code { private async Task RemoveFromLocalStorage() { await JSRuntime.InvokeVoidAsync("localStorage.removeItem", "myKey"); } }
      • Explanation: This code uses IJSRuntime to remove an item from localStorage.

  4. "How to clear all localStorage items in Blazor?"

    • Description: This query addresses clearing all items from localStorage.
    • Code:
      @page "/localstorage" @inject IJSRuntime JSRuntime <h3>LocalStorage Example</h3> <button @onclick="ClearLocalStorage">Clear All</button> @code { private async Task ClearLocalStorage() { await JSRuntime.InvokeVoidAsync("localStorage.clear"); } }
      • Explanation: This code uses IJSRuntime to clear all items from localStorage.

  5. "How to check if a key exists in localStorage using Blazor?"

    • Description: This query focuses on checking if a specific key exists in localStorage.
    • Code:
      @page "/localstorage" @inject IJSRuntime JSRuntime <h3>LocalStorage Example</h3> <button @onclick="CheckKeyExists">Check Key</button> <p>@keyExistsMessage</p> @code { private string keyExistsMessage; private async Task CheckKeyExists() { var exists = await JSRuntime.InvokeAsync<bool>("localStorage.getItem", "myKey"); keyExistsMessage = exists != null ? "Key exists" : "Key does not exist"; } }
      • Explanation: This code uses IJSRuntime to check if a key exists in localStorage and updates the message accordingly.

  6. "How to get all keys from localStorage in Blazor?"

    • Description: This query involves retrieving all keys stored in localStorage.
    • Code:
      @page "/localstorage" @inject IJSRuntime JSRuntime <h3>LocalStorage Example</h3> <button @onclick="GetAllKeys">Get All Keys</button> <ul> @foreach (var key in keys) { <li>@key</li> } </ul> @code { private List<string> keys = new List<string>(); private async Task GetAllKeys() { var keysArray = await JSRuntime.InvokeAsync<string[]>("getLocalStorageKeys"); keys = keysArray.ToList(); } } 
      // wwwroot/js/localStorageHelper.js window.getLocalStorageKeys = function() { return Object.keys(localStorage); };
      • Explanation: This code uses IJSRuntime to call a JavaScript function that retrieves all keys from localStorage.

  7. "How to check if localStorage is available in Blazor?"

    • Description: This query focuses on checking if localStorage is supported by the browser in a Blazor app.
    • Code:
      @page "/localstorage" @inject IJSRuntime JSRuntime <h3>LocalStorage Example</h3> <p>@availabilityMessage</p> @code { private string availabilityMessage; protected override async Task OnInitializedAsync() { var isAvailable = await JSRuntime.InvokeAsync<bool>("checkLocalStorageAvailability"); availabilityMessage = isAvailable ? "LocalStorage is available." : "LocalStorage is not available."; } } 
      // wwwroot/js/localStorageHelper.js window.checkLocalStorageAvailability = function() { try { var testKey = 'test'; localStorage.setItem(testKey, testKey); localStorage.removeItem(testKey); return true; } catch (e) { return false; } };
      • Explanation: This code checks if localStorage is available by using a JavaScript function that attempts to set and remove an item.

  8. "How to handle localStorage errors in Blazor?"

    • Description: This query deals with error handling when interacting with localStorage.
    • Code:
      @page "/localstorage" @inject IJSRuntime JSRuntime <h3>LocalStorage Example</h3> <button @onclick="HandleLocalStorageError">Test Error Handling</button> <p>@errorMessage</p> @code { private string errorMessage; private async Task HandleLocalStorageError() { try { await JSRuntime.InvokeVoidAsync("localStorage.setItem", "myKey", "testValue"); await JSRuntime.InvokeVoidAsync("localStorage.setItem", "myKey", new object()); // This should fail } catch (Exception ex) { errorMessage = $"Error: {ex.Message}"; } } }
      • Explanation: This code demonstrates handling errors that occur when interacting with localStorage and displaying the error message.

  9. "How to use localStorage with JSON data in Blazor?"

    • Description: This query focuses on storing and retrieving JSON data in localStorage.
    • Code:
      @page "/localstorage" @inject IJSRuntime JSRuntime <h3>LocalStorage Example</h3> <button @onclick="SaveJsonData">Save JSON</button> <button @onclick="LoadJsonData">Load JSON</button> <pre>@jsonData</pre> @code { private string jsonData; private async Task SaveJsonData() { var data = new { Name = "John", Age = 30 }; var json = JsonSerializer.Serialize(data); await JSRuntime.InvokeVoidAsync("localStorage.setItem", "jsonData", json); } private async Task LoadJsonData() { var json = await JSRuntime.InvokeAsync<string>("localStorage.getItem", "jsonData"); jsonData = json; } }
      • Explanation: This code serializes an object to JSON, stores it in localStorage, and retrieves it, displaying the JSON data.

  10. "How to synchronize localStorage access between multiple Blazor components?"

    • Description: This query addresses synchronizing localStorage access when multiple components interact with it.
    • Code:
      @page "/localstorage" @inject IJSRuntime JSRuntime <h3>LocalStorage Example</h3> <button @onclick="UpdateStorage">Update Storage</button> <button @onclick="RefreshData">Refresh Data</button> <p>@storedData</p> @code { private string storedData; private async Task UpdateStorage() { await JSRuntime.InvokeVoidAsync("localStorage.setItem", "sharedKey", "New Value"); await RefreshData(); } private async Task RefreshData() { storedData = await JSRuntime.InvokeAsync<string>("localStorage.getItem", "sharedKey"); } protected override async Task OnInitializedAsync() { await RefreshData(); } }
      • Explanation: This code demonstrates how to keep localStorage data synchronized across multiple components by refreshing the data when updated.

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