Android 第十章 RadioButton_android extends radiobutton

public class MainActivity extends AppCompatActivity {

    private RadioGroup rg_fruit;
    private RadioButton rb_1, rb_2, rb_3;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initView();
        initData();
        initClick();
    }

    private void initView() {
        rg_fruit = findViewById(R.id.rg_fruit);
        rb_1 = findViewById(R.id.radioButton);
        rb_2 = findViewById(R.id.radioButton2);
        rb_3 = findViewById(R.id.radioButton3);
    }

    private void initData() {
        //代码设置 radiobutton 是否选中
        rb_1.setChecked(true);
        rb_2.setChecked(false);
        rb_3.setChecked(false);
        //获取选中状态
        if (rb_1.isChecked()) {
            Log.d("rb_1", "true");
        }
    }

    private void initClick() {
        //radio button 状态发生改变的监听事件
        //Register a callback to be invoked when the checked radio button changes in this group
        //注册当选中的单选按钮在此组中更改时要调用的回调
        rg_fruit.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(RadioGroup group, int checkedId) {
                //group.getCheckedRadioButtonId() 获取选中后 radiobutton 按钮的id
                //checkedId 返回选中后 radioButton 按钮的id
                switch (checkedId) {
                    case R.id.radioButton:
                        Toast.makeText(MainActivity.this, "梨", Toast.LENGTH_SHORT).show();
                        break;
                    case R.id.radioButton2:
                        Toast.makeText(MainActivity.this, "香蕉", Toast.LENGTH_SHORT).show();
                        break;
                    case R.id.radioButton3:
                        Toast.makeText(MainActivity.this, "柿子", Toast.LENGTH_SHORT).show();
                        break;
                    default:
                        throw new IllegalStateException("Unexpected value: " + checkedId);
                }
            }
        });
    }
}
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<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="兄弟几个真和气，天天并肩坐一起，少时喜欢绿衣服，老来都穿黄色衣。(猜一水果)"
        android:textColor="@color/black"
        android:textSize="30sp" />

    <RadioGroup
        android:id="@+id/rg_fruit"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <RadioButton
            android:layout_marginTop="30dp"
            android:id="@+id/radioButton"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="梨"
            android:checked="true"
            android:textSize="30sp" />

        <RadioButton
            android:layout_marginTop="30dp"
            android:id="@+id/radioButton2"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="香蕉"
            android:textSize="30sp" />

        <RadioButton
            android:layout_marginTop="30dp"
            android:id="@+id/radioButton3"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="柿子"
            android:textSize="30sp" />

    </RadioGroup>
</LinearLayout>
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