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;

@Override
protected 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;

@Override
protected 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;

@Override
protected 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

@Override
protected 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;

@Override
protected 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。