[android] RadioGroup: How to check programmatically

I create a RadioGroup from XML

    <RadioGroup android:id="@+id/option" 
        android:layout_width="match_parent"
        android:orientation="horizontal" 
        android:checkedButton="@+id/block_scenario_off"
        android:layout_height="wrap_content">
        <RadioButton 
            android:layout_width="0dip"
            android:layout_weight="1" 
            android:text="@string/option1" 
            android:layout_height="wrap_content" 
            android:id="@+id/option1"
            android:layout_gravity="center|left" 
            android:onClick="@string/on_click"/>
        <RadioButton 
            android:layout_width="0dip"
            android:layout_weight="1" 
            android:text="@string/option2" 
            android:onClick="@string/on_click"
            android:layout_height="wrap_content"
            android:layout_gravity="center" 
            android:id="@+id/option2"/>
        <RadioButton 
            android:layout_width="0dip"
            android:layout_weight="1" 
            android:text="@string/option3"
            android:onClick="@string/on_click" 
            android:layout_height="wrap_content"
            android:layout_gravity="center|right" 
            android:id="@+id/option3" />
    </RadioGroup>

In Java code, I programmatically check the first one on activity creation (onCreate()) as following:

    mOption = (RadioGroup) findViewById(R.id.option);
    mOption.check(R.id.option1);

But when the activity is shown, no radio button is checked. Any help?

I use this code piece while working with indexes for radio group:

radioGroup.check(radioGroup.getChildAt(index).getId());

You may need to declare the radio buttons in the onCreate method of your code and use them.

RadioButton rb1 = (RadioButton) findViewById(R.id.option1);
rb1.setChecked(true);

it will work if you put your mOption.check(R.id.option1); into onAttachedToWindow method or like this:

view.post(new Runnable()
{
    public void run() 
    {
        // TODO Auto-generated method stub
        mOption.check(R.id.option1); 
    }
});

the reason may be that check method will only work when the radiogroup is actually rendered.

Watch out! checking the radiobutton with setChecked() is not changing the state inside the RadioGroup. For example this method from the radioGroup will return a wrong result: getCheckedRadioButtonId().

Check the radioGroup always with

mOption.check(R.id.option1);

you've been warned ;)

I prefer to use

RadioButton b = (RadioButton) findViewById(R.id.option1);
b.performClick();

instead of using the accepted answer.

RadioButton b = (RadioButton) findViewById(R.id.option1);
b.setChecked(true);

The reason is setChecked(true) only changes the checked state of radio button. It does not trigger the onClick() method added to your radio button. Sometimes this might waste your time to debug why the action related to onClick() not working.

I use this code piece while working with getId() for radio group:

radiogroup.check(radiogroup.getChildAt(0).getId());

set position as per your design of RadioGroup

hope this will help you!

Also you can use getChildAt() method. Like this:

mOption = (RadioGroup) findViewById(R.id.option);
((RadioButton)mOption.getChildAt(0)).setChecked(true);

Grab the radio group and look at the children to see if any are unchecked.

RadioGroup rg = (RadioGroup) view;
int checked = savedInstanceState.getInt(wrap.getAttributeName());

if(checked != -1) {
    RadioButton btn = (RadioButton) rg.getChildAt(checked);
    btn.toggle();
}

try this if you want your radio button to be checked based on value of some variable e.g. "genderStr" then you can use following code snippet

    if(genderStr.equals("Male"))
       genderRG.check(R.id.maleRB);
    else 
       genderRG.check(R.id.femaleRB);