不带布局的RadioGroup——NoLayoutRadioGroup

虽然android的源码也时不时的会去看，但大部分还是只能看懂部分。这里只把能完全看懂的源码上传了。 

android.widget.AnalogClock 
这个类比较简单，如果想要创建自己的View，可以从参考这个类开始。像TextView这种将近一万行的源码就太多了。还有一个比这个稍微难一点的是ImageView，也可以看那个类 

public class AnalogClock extends View {
    private Time mCalendar;

    /** 时针背景 */
    private Drawable mHourHand;
    /** 分针背景 */
    private Drawable mMinuteHand;
    /** 表盘背景 */
    private Drawable mDial;

    /** 表盘宽度 */
    private int mDialWidth;
    /** 表盘高度 */
    private int mDialHeight;

    /** 是否添加到WindowManager中 */
    private boolean mAttached;

    private final Handler mHandler = new Handler();
    private float mMinutes;
    private float mHour;
    /** 时间是否改变了 */
    private boolean mChanged;

    public AnalogClock(Context context) {
        this(context, null);
    }

    public AnalogClock(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public AnalogClock(Context context, AttributeSet attrs,
                       int defStyle) {
        super(context, attrs, defStyle);
        Resources r = mContext.getResources();
        TypedArray a =
                context.obtainStyledAttributes(
                        attrs, com.android.internal.R.styleable.AnalogClock, defStyle, 0);

        mDial = a.getDrawable(com.android.internal.R.styleable.AnalogClock_dial);
        if (mDial == null) {
            mDial = r.getDrawable(com.android.internal.R.drawable.clock_dial);
        }

        mHourHand = a.getDrawable(com.android.internal.R.styleable.AnalogClock_hand_hour);
        if (mHourHand == null) {
            mHourHand = r.getDrawable(com.android.internal.R.drawable.clock_hand_hour);
        }

        mMinuteHand = a.getDrawable(com.android.internal.R.styleable.AnalogClock_hand_minute);
        if (mMinuteHand == null) {
            mMinuteHand = r.getDrawable(com.android.internal.R.drawable.clock_hand_minute);
        }

        mCalendar = new Time();

        mDialWidth = mDial.getIntrinsicWidth();
        mDialHeight = mDial.getIntrinsicHeight();
    }

    @Override
    protected void onAttachedToWindow() {
        super.onAttachedToWindow();

        if (!mAttached) {
            mAttached = true;
            IntentFilter filter = new IntentFilter();

            filter.addAction(Intent.ACTION_TIME_TICK);
            filter.addAction(Intent.ACTION_TIME_CHANGED);
            filter.addAction(Intent.ACTION_TIMEZONE_CHANGED);

            getContext().registerReceiver(mIntentReceiver, filter, null, mHandler);
        }

        // NOTE: It's safe to do these after registering the receiver since the receiver always runs
        // in the main thread, therefore the receiver can't run before this method returns.

        // The time zone may have changed while the receiver wasn't registered, so update the Time
        mCalendar = new Time();

        // Make sure we update to the current time
        onTimeChanged();
    }

    @Override
    protected void onDetachedFromWindow() {
        super.onDetachedFromWindow();
        if (mAttached) {
            getContext().unregisterReceiver(mIntentReceiver);
            mAttached = false;
        }
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

        int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        // layout提供的可用Width
        int widthSize =  MeasureSpec.getSize(widthMeasureSpec);
        int heightMode = MeasureSpec.getMode(heightMeasureSpec);
        // layout提供的可用Height
        int heightSize =  MeasureSpec.getSize(heightMeasureSpec);

        float hScale = 1.0f;
        float vScale = 1.0f;

        // 如果layout_width和layout_height是指定了值的
        if (widthMode != MeasureSpec.UNSPECIFIED && widthSize < mDialWidth) {
            hScale = (float) widthSize / (float) mDialWidth;
        }

        if (heightMode != MeasureSpec.UNSPECIFIED && heightSize < mDialHeight) {
            vScale = (float )heightSize / (float) mDialHeight;
        }

        // 按照缩的比较小的缩放
        float scale = Math.min(hScale, vScale);

        setMeasuredDimension(resolveSize((int) (mDialWidth * scale), widthMeasureSpec),
                resolveSize((int) (mDialHeight * scale), heightMeasureSpec));
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        mChanged = true;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        boolean changed = mChanged;
        if (changed) {
            mChanged = false;
        }

        int availableWidth = mRight - mLeft;
        int availableHeight = mBottom - mTop;

        // 居中
        int x = availableWidth / 2;
        int y = availableHeight / 2;

        final Drawable dial = mDial;
        int w = dial.getIntrinsicWidth();
        int h = dial.getIntrinsicHeight();

        boolean scaled = false;

        // 图片实际宽高比view的宽高大时，要对图片缩放
        if (availableWidth < w || availableHeight < h) {
            scaled = true;
            float scale = Math.min((float) availableWidth / (float) w,
                                   (float) availableHeight / (float) h);
            canvas.save();
            canvas.scale(scale, scale, x, y);
        }

        if (changed) {
            dial.setBounds(x - (w / 2), y - (h / 2), x + (w / 2), y + (h / 2));
        }
        dial.draw(canvas);

        // 绘制时针
        canvas.save();
        canvas.rotate(mHour / 12.0f * 360.0f, x, y);
        final Drawable hourHand = mHourHand;
        if (changed) {
            w = hourHand.getIntrinsicWidth();
            h = hourHand.getIntrinsicHeight();
            hourHand.setBounds(x - (w / 2), y - (h / 2), x + (w / 2), y + (h / 2));
        }
        hourHand.draw(canvas);
        canvas.restore();

        // 绘制分针
        canvas.save();
        canvas.rotate(mMinutes / 60.0f * 360.0f, x, y);

        final Drawable minuteHand = mMinuteHand;
        if (changed) {
            w = minuteHand.getIntrinsicWidth();
            h = minuteHand.getIntrinsicHeight();
            minuteHand.setBounds(x - (w / 2), y - (h / 2), x + (w / 2), y + (h / 2));
        }
        minuteHand.draw(canvas);
        canvas.restore();

        // 结束
        if (scaled) {
            canvas.restore();
        }
    }

    private void onTimeChanged() {
        mCalendar.setToNow();

        int hour = mCalendar.hour;
        int minute = mCalendar.minute;
        int second = mCalendar.second;

        mMinutes = minute + second / 60.0f;
        mHour = hour + mMinutes / 60.0f;
        mChanged = true;
    }

    private final BroadcastReceiver mIntentReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            if (intent.getAction().equals(Intent.ACTION_TIMEZONE_CHANGED)) {
                String tz = intent.getStringExtra("time-zone");
                mCalendar = new Time(TimeZone.getTimeZone(tz).getID());
            }

            onTimeChanged();

            invalidate();
        }
    };
}

不带布局的RadioGroup——NoLayoutRadioGroup 
android提供的RadioGroup是一个LinearLayout，有时我们要在像TableLayout中的每个行使用一个RadioButton的话，RadioGroup就不太好用，所以参考RadioGroup实现了一个不带布局的RadioGroup. 

/***
 * 使用了这个类，RadioButton的OnCheckedChangeListener会被覆盖掉，所以
 * 要使用监听器的话，使用这边的NonLayoutRadioGroup.OnCheckedChangeListener
 */
public class NonLayoutRadioGroup {
    public interface OnCheckedChangeListener {
        /***
         * @param group 触发该事件的NonLayoutRadioGroup
         * @param view 触发该事件的RadioButton, 当调用clearCheck时，view的值为null
         */
        public void onCheckedChanged(NonLayoutRadioGroup group, RadioButton view);
    }

    private List<RadioButton> mRadioButtons = new ArrayList<RadioButton>();

    private RadioButton mCheckButton;

    private OnCheckedChangeListener mListener;

    private CompoundButton.OnCheckedChangeListener mCheckedListener =
            new CompoundButton.OnCheckedChangeListener() {
        @Override
        public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
            if (!isChecked) {
                mCheckButton = null;
                return;
            }
            if (mCheckButton != null) {
                mCheckButton.setChecked(false);
            }

            setCheckedButton((RadioButton) buttonView);
        }
    };

    public void addRadioButton(RadioButton button) {
        // 不能添加null
        // 为没有id的RadioButton生成一个Id
        if (button.getId() == View.NO_ID) {
            button.setId(button.hashCode());
        }
        button.setOnCheckedChangeListener(null);
        if (button.isChecked()) {
            // 移除原来的
            if (mCheckButton != null) {
                mCheckButton.setChecked(false);
            }

            setCheckedButton(button);
        }
        button.setOnCheckedChangeListener(mCheckedListener);
        mRadioButtons.add(button);
    }

    public void removeRadioButton(RadioButton button) {
        // 添加到这里面的移除时，才需要清除其OnCheckedChangeListener
        if (mRadioButtons.contains(button)) {
            button.setOnCheckedChangeListener(null);
            mRadioButtons.remove(button);
        }
    }

    public void setOnCheckedChangeListener(OnCheckedChangeListener listener) {
        mListener = listener;
    }

    public void check(RadioButton button) {
        // check原来选中的
        if (button != null && mCheckButton == button) {
            return;
        }
        // 移除选中的
        if (mCheckButton != null) {
            mCheckButton.setChecked(false);
        }
        // 设置选中的
        if (button != null) {
            button.setChecked(true);
        }
        // 触发监听器
        setCheckedButton(button);
    }

    public void clearCheck() {
        check(null);
    }

    public RadioButton getCheckedRadioButton() {
        return mCheckButton;
    }

    // ////////////////////////////////////////////////
    /***
     * 设置选中的RadioButton
     */
    private void setCheckedButton(RadioButton button) {
        mCheckButton = button;
        if (mListener != null) {
            if (button != null) {
                mListener.onCheckedChanged(this, button);
            }
            else {
                mListener.onCheckedChanged(this, null);
            }
        }
    }
}