Android RadioButton和CheckBox控件

1. RadioButton类

RadioButton继承CompoundButton，是单选按钮。
android:checked设置按钮是否选中。用setOnCheckChangeLinstener来对单选按钮进行监听。

RadioButton选择以后不能取消，主要是它覆盖了toggle方法，使其在被选中后无法取消。但可通过setChecked()方法取消。

public class RadioButton extends CompoundButton {
    @Override
    public void toggle() {
        // we override to prevent toggle when the radio is already
        // checked (as opposed to check boxes widgets)
        if (!isChecked()) {
            super.toggle();
        }
    }
}

RadioButton可以和RadioGroup配合使用，RadioButton只可以选择一个从而达到了单选的目的。android:checkedButton指定初始选项。

<RadioGroup
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:checkedButton="@+id/rb1">
    <RadioButton
        android:id="@+id/rb1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="足球"/>
    <RadioButton
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="篮球"/>
</RadioGroup>

在RadioGroup的构造方法中，调用了init()方法，指定CheckedStateTracker和PassThroughHierarchyChangeListener。

private void init() {
    mChildOnCheckedChangeListener = new CheckedStateTracker();
    mPassThroughListener = new PassThroughHierarchyChangeListener();
    super.setOnHierarchyChangeListener(mPassThroughListener);
}

PassThroughHierarchyChangeListener类监听RadioGroup下View的状态，对每个RadioButton添加CheckedStateTracker监听器。

private class PassThroughHierarchyChangeListener implements
        ViewGroup.OnHierarchyChangeListener {

    @Override
    public void onChildViewAdded(View parent, View child) {
        if (parent == RadioGroup.this && child instanceof RadioButton) {
            int id = child.getId();
            // generates an id if it's missing
            if (id == View.NO_ID) {
                id = View.generateViewId();
                child.setId(id);
            }
            ((RadioButton) child).setOnCheckedChangeWidgetListener(
                    mChildOnCheckedChangeListener);
        }

        if (mOnHierarchyChangeListener != null) {
            mOnHierarchyChangeListener.onChildViewAdded(parent, child);
        }
    }
}

CheckedStateTracker类，取消原来的选项并设置新的选项。

private class CheckedStateTracker implements CompoundButton.OnCheckedChangeListener {
    @Override
    public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
        // prevents from infinite recursion
        if (mProtectFromCheckedChange) {
            return;
        }

        mProtectFromCheckedChange = true;
        if (mCheckedId != -1) {
            setCheckedStateForView(mCheckedId, false);
        }
        mProtectFromCheckedChange = false;

        int id = buttonView.getId();
        setCheckedId(id);
    }
}

// 取消原来的选项
private void setCheckedStateForView(int viewId, boolean checked) {
    View checkedView = findViewById(viewId);
    if (checkedView != null && checkedView instanceof RadioButton) {
        ((RadioButton) checkedView).setChecked(checked);
    }
}

// 设置新的选项
private void setCheckedId(@IdRes int id) {
    mCheckedId = id;
    if (mOnCheckedChangeListener != null) {
        mOnCheckedChangeListener.onCheckedChanged(this, mCheckedId);
    }
    final AutofillManager afm = mContext.getSystemService(AutofillManager.class);
    if (afm != null) {
        afm.notifyValueChanged(this);
    }
}

2. CheckBox类

CheckBox继承CompoundButton，是多选按钮。
android:checked设置按钮是否选中。用setOnCheckChangeLinstener来对单选按钮进行监听。

3. 自定义按钮

RadioButton和CheckBox可以通过android:button指定按钮样式。样式文件，

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:state_checked="true"
        android:drawable="@drawable/checkbox_s" />
    <item android:state_pressed="true"
        android:drawable="@drawable/checkbox_s" />
    <item
        android:drawable="@drawable/checkbox" />
</selector>