Android中RadioGroup取值与全局变量赋值问题求助

Hey there! Since you're new to Android and Java coming from C#, let's break down what's going wrong and fix this step by step.

First: The Core Problem in Your Radio Button Click Code #

Looking at your current onRadioButtonClicked method, you're not actually assigning any value to your global category variable at all! Plus, the structure of your switch case has a common Java pitfall (fall-through) that would cause unexpected behavior even if you did add assignments.

Here's what's wrong with your original code:

• You check if the radio button is checked, but then just break without setting category
• If a radio button isn't checked (which happens automatically when another one is selected), the code will fall through to the next case, which isn't what you want

Corrected Click Event Code #

First, make sure your global variable is initialized to avoid null values:

public String category = ""; // Initialize to empty string instead of leaving it unassigned

Then update your click handler to actually set the category value when a radio button is selected:

public void onRadioButtonClicked(View view) { 
    boolean checked = ((RadioButton) view).isChecked(); 

    // Only act when the radio button is being checked (since unchecking is automatic)
    if (checked) {
        switch (view.getId()) { 
            case R.id.film: 
                category = "film";
                break; 
            case R.id.actor: 
                category = "actor";
                break; 
            case R.id.actress: 
                category = "actress";
                break; 
            case R.id.editing: 
                category = "editing";
                break; 
            case R.id.effects: 
                category = "effects";
                break; 
            default:
                category = ""; // Fallback if no valid selection
                break;
        }
    }
}

Second: Fixing the ???? Submission Issue #

Once category is correctly assigned, the ???? usually points to an encoding problem when sending the data via Volley. Make sure your request uses UTF-8 encoding to handle the string correctly.

Here's an example of a properly configured Volley POST request:

// Replace YOUR_SERVER_URL with your actual endpoint
StringRequest postRequest = new StringRequest(Request.Method.POST, YOUR_SERVER_URL,
    response -> {
        // Handle successful response here
    },
    error -> {
        // Handle error here
    }
) {
    @Override
    protected Map<String, String> getParams() {
        Map<String, String> params = new HashMap<>();
        params.put("category", category); // Now this has the correct selected value
        return params;
    }

    @Override
    public Map<String, String> getHeaders() throws AuthFailureError {
        Map<String, String> headers = new HashMap<>();
        // Ensure UTF-8 encoding for the request
        headers.put("Content-Type", "application/x-www-form-urlencoded; charset=UTF-8");
        return headers;
    }
};

// Add the request to Volley's queue
RequestQueue queue = Volley.newRequestQueue(this);
queue.add(postRequest);

Quick Tips for C# Developers Moving to Java #

• Unlike C#, Java allows fall-through in switch cases (if you don't add break, code will continue to the next case). Always remember to add break after each case unless you intentionally want fall-through.
• Uninitialized variables in Java can cause null pointer issues, so always initialize your global variables (like category = "" instead of just String category;).
• Make sure each RadioButton in your layout has android:onClick="onRadioButtonClicked" set, otherwise the click event won't trigger.

内容的提问来源于stack exchange，提问作者tarku