Xamarin Android Binding中调用中间件及设置Jar私有字段方法咨询

Hey there! Let's tackle your Xamarin Android Binding questions one by one:

First, when you mention "middleware functions", I assume you're referring to methods in your target JAR that either aren't exposed by default in the generated C# binding, or live in a helper/middleware class within the library. Here's how to work with them:

• Adjust Binding Metadata (for hidden methods)
  Sometimes the Xamarin binding generator marks certain methods as internal or skips them entirely. Fix this by editing the Metadata.xml file in your Binding project. For example, if your middleware method processData lives in com.example.Middleware, add this entry:

  <attr path="/api/package[@name='com.example']/class[@name='Middleware']/method[@name='processData' and count(parameter)=1 and parameter[1][@type='java.lang.String']]" name="visibility">public</attr>
  

  This forces the generator to create a public C# wrapper for the method.

• Extend with Partial Classes
  If the generated binding class is marked as partial, you can add a separate .cs file in your Binding project to create cleaner wrappers:

  public partial class Middleware
  {
      public string ProcessUserInput(string input)
      {
          // Call the underlying middleware method directly
          return ProcessData(input);
      }
  }
  

• Direct Call (once exposed)
  Once the method is properly bound, call it like any regular C# method:

  var middleware = new Middleware();
  var processedResult = middleware.ProcessData("your_input_here");
  

Accessing private fields requires using Java Reflection, but you can do this silently in the background without user input. Here's a practical implementation:

• Reflection Helper Method
  Use Xamarin's access to Java reflection APIs to unlock and modify the private field:

  using Java.Lang.Reflect;
  
  private void UpdatePrivateField(object targetInstance, string fieldName, object newValue)
  {
      try
      {
          Class targetClass = targetInstance.Class;
          // Get the private field (pass true to include non-public members)
          Field privateField = targetClass.GetDeclaredField(fieldName);
          // Enable access to the private field
          privateField.Accessible = true;
          // Set the new value
          privateField.Set(targetInstance, newValue);
      }
      catch (NoSuchFieldException ex)
      {
          System.Diagnostics.Debug.WriteLine($"Field not found: {ex.Message}");
      }
      catch (IllegalAccessException ex)
      {
          System.Diagnostics.Debug.WriteLine($"Access denied: {ex.Message}");
      }
  }
  

• Run in the Background
  Execute this logic on a background thread to avoid blocking the UI and keep it invisible to the user:

  // Get an instance of the JAR class you need to modify
  var jarClassInstance = new com.example.MyJarClass();
  
  // Run the field update in the background
  Task.Run(() =>
  {
      UpdatePrivateField(jarClassInstance, "privateFieldName", "new_field_value");
  });
  

• Key Notes

  • Use the exact case-sensitive Java field name as it exists in the JAR.
  • Reflection is fragile: if the JAR updates and changes the field name/access level, your code will break.
  • Most standard Android environments allow this, but some security-restricted setups might block reflection.

内容的提问来源于stack exchange，提问作者solidak