Android Studio：使用radioButtons进行测验

Question

So I'm trying to make an app where you select an answer from a radioButton within a radioGroup , and when you hit the Submit button it will change the textbox to say "Correct" or "Wrong answer", depending on which button was selected. I'm able to run the app, and select the radioButton , but when I click submit, the app crashes and says "Unfortunately, MyApp has stopped".

This is the code that I have:

XML

 <RadioGroup
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@id/question1"
    android:id="@+id/q1radiobox">

        <RadioButton
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/q1a1"
            android:id="@+id/q1a1" />
        <RadioButton
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/q1a2"
            android:id="@+id/q1a2"/>
        <RadioButton
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/q1a3"
            android:id="@+id/q1a3"/>
        <RadioButton
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/q1a4"
            android:id="@+id/q1a4"/>
    </RadioGroup>

    <Button
        android:onClick="checkResult"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/q1radiobox"
        android:text="Submit"/>

Java

   private void checkResult() {
      RadioButton rb;
      rb = (RadioButton) findViewById(R.id.q1a3);

      if (rb.isChecked()) {
        ((TextView) findViewById(R.id.answer1)).setText("@string/correct");
      } 
      else {
          ((TextView) findViewById(R.id.answer1)).setText("@string/incorrect");
    }
} 

Any help would be greatly appreciated; I can't work out what's wrong!

EDIT: I have posted the solution. Credit to @miselking for pointing out one of the issues.

Answer 1

Ok, so what you need to know it that when you are using android:onClick="checkResult" way of defining the click events, your checkResult method needs to have the View as an argument, only then it can respond to onClick events. So, change your method to something like this:

    private void checkResult(View v) {
      RadioButton rb;
      rb = (RadioButton) findViewById(R.id.q1a3);

      if (rb.isChecked()) {
        ((TextView) findViewById(R.id.answer1)).setText("@string/correct");
      } 
      else {
          ((TextView) findViewById(R.id.answer1)).setText("@string/incorrect");
    }

EDIT: What you are getting is a warning, not an error. You are getting that warning because you are not using the parameter v anywhere in your method. You can ignore it, it is usefull if you have multiple buttons invoking the same method, then you need to know which button actually invoked the method.

Let's say you have two buttons with ids btnId1 and btnId2 . Both of them have this line of code in xml file: android:onClick="checkResult" , so both of them call the same method (you can do that). Then, when you click any of these two buttons, which one actually invoked the method? Well, that is why the View v is neccessary. Then, you would have been able to see which button was actually clicked and responded appropriatelly. Example of implementation of the checkResult :

public void checkResult(View view)
    {
        Log.d("TAG_BTN", "Someone called me. But who???");
        switch (view.getId())
        {
            case R.id.btnId1:
                Log.d("TAG_BTN", "BtnId1 called me. Do something, please...");
                break;
            case R.id.btnId2:
                Log.d("TAG_BTN", "BtnId2 called me. What next to do...");
                break;
        }
    }

Hopefully, you know understand why you need the View parameter.

Answer 2

So after all of this hassle, I have found that the issues were as follows:

 private void checkResult()

Needed to be

public void checkResult(View view)

Thank you to @miselking for pointing out the lack of a view, and I found the public/private void by pure luck, when playing around with the method.