RadioButton使用方法

学一点，记一点。

要点

• 一组Radio Button放到一个Radio Group中；
• 如果Radio Button很多，就考虑是否Spinner更合适
• 事件处理有多种方式，如RadioGroup的OnCheckedChangeListener。

示例

效果

功能

选择某一个Radio Button之后，下面一个TextView显示选择结果。

布局文件 my_layout.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="vertical" >    <RadioGroup        android:id="@+id/radio_group"        android:layout_width="457dp"        android:layout_height="wrap_content"        android:orientation="horizontal" >        <RadioButton            android:id="@+id/radio_first"            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:checked="true"            android:text="@string/first" />        <RadioButton            android:id="@+id/radio_second"            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:text="@string/second" />        <RadioButton            android:id="@+id/radio_third"            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:text="@string/third" />    </RadioGroup>    <TextView        android:id="@+id/select_result"        android:layout_width="match_parent"        android:layout_height="wrap_content"/></LinearLayout>

代码

省略掉自动生成的代码。

private RadioGroup radioGroup = null;private TextView textView = null;@Overrideprotected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.my_layout);    radioGroup = (RadioGroup) this.findViewById(R.id.radio_group);    textView = (TextView) this.findViewById(R.id.select_result);    textView.setText(getSelectedInfo());    radioGroup.setOnCheckedChangeListener(new OnCheckedChangeListener() {        public void onCheckedChanged(RadioGroup group, int checkedId) {            textView.setText(getSelectedInfo(checkedId));        }    });}private String getSelectedInfo() {    int checkedId = radioGroup.getCheckedRadioButtonId();    return getSelectedInfo(checkedId);}private String getSelectedInfo(int checkedId) {    String selected = "Unknown selection!";    switch (checkedId) {    case R.id.radio_first:        selected = "First was selected.";        break;    case R.id.radio_second:        selected = "Second was selected.";        break;    case R.id.radio_third:        selected = "Third was selected.";        break;    default:        break;    }    return selected;}

事件处理

上面的示例是为RadioGroup对象注册OnCheckedChangeListener。此外，还可以直接为每个Radio Button注册listener。接下来详细描述。

RadioButton事件处理

可以为Radio Button注册CompoundButton.OnCheckedChangeListener。

代码一

private RadioButton firstRadio = null;private RadioButton secondRadio = null;private RadioButton thirdRadio = null;@Overrideprotected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.my_layout);    firstRadio = (RadioButton) this.findViewById(R.id.radio_first);    secondRadio = (RadioButton) this.findViewById(R.id.radio_second);    thirdRadio = (RadioButton) this.findViewById(R.id.radio_third);    firstRadio.setOnCheckedChangeListener(new MyListener("First"));    secondRadio.setOnCheckedChangeListener(new MyListener("Second"));    thirdRadio.setOnCheckedChangeListener(new MyListener("Third"));}private class MyListener implements CompoundButton.OnCheckedChangeListener {    private String radioName = null;    public MyListener(String theRadioName) {        radioName = theRadioName;    }    public void onCheckedChanged(CompoundButton buttonView,            boolean isChecked) {        Toast.makeText(MainActivity.this, radioName + " checked:" + isChecked, Toast.LENGTH_SHORT).show();    }}

实际运行发现，被选中的Radio Button会先处理，显示：xxx checked: true；失去焦点的Radio Button之后处理，显示：xxx checked: false。

注意到，这里通过ctor传入一个标识符，说明当前的事件处理是哪个Radio Button的。显然，这种方式的通用性并不好。

代码二

下面是等价的一种方式：

private RadioButton firstRadio = null;private RadioButton secondRadio = null;private RadioButton thirdRadio = null;@Overrideprotected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.my_layout);    firstRadio = (RadioButton) this.findViewById(R.id.radio_first);    secondRadio = (RadioButton) this.findViewById(R.id.radio_second);    thirdRadio = (RadioButton) this.findViewById(R.id.radio_third);    MyListener listener = new MyListener();    firstRadio.setOnCheckedChangeListener(listener);    secondRadio.setOnCheckedChangeListener(listener);    thirdRadio.setOnCheckedChangeListener(listener);}private String getRadioName(int id) {    switch (id) {    case R.id.radio_first: return "First";    case R.id.radio_second: return "Second";    case R.id.radio_third: return "Third";    default: return "Unknown";    }}private class MyListener implements CompoundButton.OnCheckedChangeListener {    public void onCheckedChanged(CompoundButton buttonView,            boolean isChecked) {        String radioName = getRadioName(buttonView.getId());        Toast.makeText(MainActivity.this, radioName + " checked:" + isChecked, Toast.LENGTH_SHORT).show();    }}

xml中定义事件

在docs/guide/topics/ui/controls/radiobutton.html中提到在xml中定义Radio Button的事件处理。

xml

在每个RadioButton中增加一个属性：

android:onClick="onRadioButtonClicked"

即变成下面的样子：

<RadioGroup    android:id="@+id/radio_group"    android:layout_width="457dp"    android:layout_height="wrap_content"    android:orientation="horizontal" >    <RadioButton        android:id="@+id/radio_first"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:checked="true"        android:text="@string/first"        android:onClick="onRadioButtonClicked" />    <RadioButton        android:id="@+id/radio_second"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="@string/second"        android:onClick="onRadioButtonClicked" />    <RadioButton        android:id="@+id/radio_third"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="@string/third"        android:onClick="onRadioButtonClicked" /></RadioGroup>

代码

@Overrideprotected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.my_layout);}private String getRadioName(int id) {    switch (id) {    case R.id.radio_first: return "First";    case R.id.radio_second: return "Second";    case R.id.radio_third: return "Third";    default: return "Unknown";    }}public void onRadioButtonClicked(View view) {    boolean checked = ((RadioButton) view).isChecked();    String radioName = getRadioName(view.getId());    Toast.makeText(this, radioName + " checked:" + checked,             Toast.LENGTH_SHORT).show();}

运行效果

当选中某个Radio Button的时候，会触发事件。失去焦点的不会触发事件，——因为是OnClick类型的事件，而不是OnCheckedChanged。

所以，这种方法比前一种要简洁得多。

在代码中注册OnClickListener

另外一种等价方式就是直接在代码中为RadioButton注册OnClickListener对象。

为此，在xml中删除前面添加的属性，然后代码改成如下的样子：

private RadioButton firstRadio = null;private RadioButton secondRadio = null;private RadioButton thirdRadio = null;@Overrideprotected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.my_layout);    OnClickListener listener = new OnClickListener() {        public void onClick(View view) {            boolean checked = ((RadioButton) view).isChecked();            String radioName = getRadioName(view.getId());            Toast.makeText(MainActivity.this, radioName + " checked:" + checked,                     Toast.LENGTH_SHORT).show();        }    };    firstRadio = (RadioButton) this.findViewById(R.id.radio_first);    secondRadio = (RadioButton) this.findViewById(R.id.radio_second);    thirdRadio = (RadioButton) this.findViewById(R.id.radio_third);    firstRadio.setOnClickListener(listener);    secondRadio.setOnClickListener(listener);    thirdRadio.setOnClickListener(listener);}private String getRadioName(int id) {    switch (id) {    case R.id.radio_first: return "First";    case R.id.radio_second: return "Second";    case R.id.radio_third: return "Third";    default: return "Unknown";    }}

对比分析

以下两种方法比较好：

• 为Radio Group注册OnCheckedChangeListener
• 为Radio Button注册OnClickListener

注意点：OnXyzListener会在不同的class中存在，有时候需要认真区分，必要情况下用ClassName.OnXyzListener的方式来引用。