SeekBar

SeekBar通过设置Widget.AppCompat.SeekBar.Discrete主题可以实现离散值选择。

<androidx.appcompat.widget.AppCompatSeekBar
        android:id="@+id/seekBar"
        style="@style/Widget.AppCompat.SeekBar.Discrete"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:max="4"
        android:maxHeight="4dp"
        android:progress="3"
        android:progressDrawable="@drawable/progress"
        android:thumb="@drawable/thumb"
        app:tickMark="@drawable/tickmark" />

对应的progress.xml资源：

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:id="@android:id/background">
        <shape>
            <corners android:radius="20dp" />
            <solid android:color="#DCDCDC" />
        </shape>
    </item>
    <item android:id="@android:id/progress">
        <clip>
            <shape>
                <corners android:radius="20dp" />
                <solid android:color="#A7F2AA" />
            </shape>
        </clip>
    </item>
</layer-list>

对应的thumb.xml资源：

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item>
        <shape android:shape="oval">
            <solid android:color="#BBEEBD" />
            <size
                android:width="15dp"
                android:height="15dp" />
        </shape>
    </item>

    <item
        android:bottom="5dp"
        android:left="5dp"
        android:right="5dp"
        android:top="5dp">
        <shape android:shape="oval">
            <solid android:color="#21B827" />
            <size
                android:width="10dp"
                android:height="10dp" />
        </shape>
    </item>
</layer-list>

对应的tickmark.xml资源：

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="oval">

    <solid android:color="#72EA77" />
    <size
        android:width="10dp"
        android:height="10dp" />
</shape>

Slider

Slider是Material Design库中的控件。具体引入方式如下：

	implementation 'com.google.android.material:material:1.4.0'

Slider既可以用作连续滑块，也可以用作离散滑块。操作模式由步长的值控制。如果步长设置为 0，则滑块作为连续滑块运行，滑块可以沿水平线移动到任何位置。如果步长设置为大于 0 的数字，则滑块作为离散滑块运行，滑块将捕捉到最接近的有效值。
Slider在滑动时可以展示指示标签。LabelFormatter接口用于定义在交互时呈现在指示标签内文本的格式。
使用默认样式com.google.android.material.R.style#Widget_MaterialComponents_Slider，使用colorPrimary和colorOnPrimary自定义滑块的颜色，使用colorOnSurface定义禁用状态颜色。以下属性用于进一步自定义滑块的外观：

haloColor：thumb周围光环的颜色
haloRadius：thumb周围光环的半径
labelBehavior：标签的行为，可以是LABEL_FLOATING，LABEL_WITHIN_BOUNDS或LABEL_GONE
labelStyle：应用于值指示器TooltipDrawable的样式
thumbColor：thumb的颜色
thumbStrokeColor：thumb的描边颜色
thumbStrokeWidth：thumb的描边宽度
thumbElevation：thumb的描边高度
thumbRadius：thumb的半径
tickColorActive：滑过部分的刻度颜色。仅在滑块处于离散模式时使用
tickColorInactive：滑块未滑过部分的刻度线颜色。仅在滑块处于离散模式时使用
tickColor：滑块刻度线的颜色。仅当滑块在离散模式。当tickColorActive和tickColorInactive相同时可以只设置此值，优先于tickColorActive和tickColorInactive
tickVisible：是否显示刻度线。仅当滑块在离散模式
trackColorActive：轨道滑过部分的颜色
trackColorInactive：轨道未滑过部分的颜色
trackColor：整个轨道的颜色。当trackColorActive和trackColorInactive相同时可以只设置此值。优先于trackColorActive和trackColorInactive
trackHeight：轨道高度
android:valueFrom：必需。滑块的最小值，此值必须小于valueTo
android:valueTo：必需。滑块的最大值，此值必须大于valueFrom
android:value：可选。滑块的初始值
android:stepSize：可选。该值表示滑块是否操作在连续模式或离散模式下。如果缺失或等于 0，则滑块在连续模式。如果大于0并均匀划分valueFrom和valueTo，滑块在离散模式下运行

对应的使用方式如下：

<com.google.android.material.slider.Slider
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:stepSize="1"
        android:value="3"
        android:valueFrom="0"
        android:valueTo="4"
        app:haloColor="@color/black"
        app:haloRadius="8dp"
        app:thumbColor="#60C664"
        app:thumbRadius="8dp"
        app:tickColor="#60C664"
        app:tickColorActive="#22B528"
        app:tickColorInactive="#A0AAA0"
        app:tickVisible="true"
        app:trackColor="#60C664"
        app:trackColorActive="#22B528"
        app:trackColorInactive="#A0AAA0"
        app:trackHeight="4dp" />

自定义控件

通过继承View进行自定义离散滑动控件。

public class DiscreteSeekBar extends View {

    public interface OnDiscreteValueChangedListener {
        void onValueChanged(DiscreteSeekBar seekBar, int value);
    }

    private Drawable mThumb;
    private Drawable mTrackActive;
    private Drawable mTrackInactive;
    private Drawable mTickMarkActive;
    private Drawable mTickMarkInactive;
    private int mTrackHeight;
    private int mLabelTextColor;
    private int mLabelTextSize;
    private int mLabelPadding;

    private List<Rect> mTickRectList = new ArrayList<>();

    private List<String> mTickLabelList = new ArrayList<>();
    private int mLabelCount = 0;

    private Paint mPaint;
    private Paint mLabelPaint;

    private int mValue;
    private int mValueFrom;
    private int mValueTo;
    private int mStepSize;

    private Rect mRect = new Rect();

    private OnDiscreteValueChangedListener mOnDiscreteValueChangedListener;

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

    public DiscreteSeekBar(Context context, @Nullable AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public DiscreteSeekBar(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);

        TypedArray ta = context.obtainStyledAttributes(attrs, R.styleable.DiscreteSeekBar, defStyleAttr, 0);
        mThumb = ta.getDrawable(R.styleable.DiscreteSeekBar_android_thumb);
        mTrackActive = ta.getDrawable(R.styleable.DiscreteSeekBar_trackActive);
        mTrackInactive = ta.getDrawable(R.styleable.DiscreteSeekBar_trackInactive);
        mTickMarkActive = ta.getDrawable(R.styleable.DiscreteSeekBar_tickMarkActive);
        mTickMarkInactive = ta.getDrawable(R.styleable.DiscreteSeekBar_tickMarkInactive);
        mTrackHeight = ta.getDimensionPixelSize(R.styleable.DiscreteSeekBar_trackHeight, 4);
        mLabelTextColor = ta.getColor(R.styleable.DiscreteSeekBar_labelTextColor, Color.BLACK);
        mLabelTextSize = ta.getDimensionPixelSize(R.styleable.DiscreteSeekBar_labelTextSize, 16);
        mLabelPadding = ta.getDimensionPixelSize(R.styleable.DiscreteSeekBar_labelPadding, 0);
        mValueFrom = (int) ta.getFloat(R.styleable.DiscreteSeekBar_android_valueFrom, 0f);
        mValueTo = (int) ta.getFloat(R.styleable.DiscreteSeekBar_android_valueTo, 10f);
        mValue = (int) ta.getFloat(R.styleable.DiscreteSeekBar_android_value, mValueFrom);
        mStepSize = (int) ta.getFloat(R.styleable.DiscreteSeekBar_android_stepSize, 1);
        ta.recycle();

        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mPaint.setStrokeCap(Paint.Cap.ROUND);
        mPaint.setStrokeJoin(Paint.Join.ROUND);
        mPaint.setStrokeWidth(mTrackHeight);
        mPaint.setColor(Color.RED);

        mLabelPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mLabelPaint.setTextSize(mLabelTextSize);
        mLabelPaint.setColor(mLabelTextColor);
    }

    public int getLabelPadding() {
        return this.mLabelPadding;
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        int dw = MeasureSpec.getSize(widthMeasureSpec);
        int dh = MeasureSpec.getSize(heightMeasureSpec);

        final Drawable d = mThumb;
        if (d != null) {
            dh = Math.max(dh, d.getIntrinsicHeight());
        }

        int labelHeight = 0;
        if (mLabelCount != 0) {
            Paint.FontMetrics fm = mLabelPaint.getFontMetrics();
            labelHeight = (int) Math.ceil(fm.bottom - fm.top);
        }

        dh += getPaddingTop() + getPaddingBottom() + getLabelPadding() + labelHeight;

        final int measuredWidth = resolveSizeAndState(dw, widthMeasureSpec, 0);
        final int measuredHeight = resolveSizeAndState(dh, heightMeasureSpec, 0);
        setMeasuredDimension(measuredWidth, measuredHeight);
    }

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

        mTickRectList.clear();
        if (mThumb != null) {
            final int count = getTickCount();
            int tickPadding;
            if (mLabelCount > 0) {
                int start = Math.max((int) Math.ceil(mLabelPaint.measureText(mTickLabelList.get(0))), mThumb.getIntrinsicWidth()) >> 1;
                int end = Math.max((int) Math.ceil(mLabelPaint.measureText(mTickLabelList.get(mLabelCount - 1))), mThumb.getIntrinsicWidth()) >> 1;
                tickPadding = (w - start - end - getPaddingLeft() - getPaddingRight()) / (count - 1);
            } else {
                tickPadding = (w - mThumb.getIntrinsicWidth() - getPaddingLeft() - getPaddingRight()) / (count - 1);
            }
            for (int i = 0; i < count; i++) {
                Rect rect = new Rect();
                rect.left = getPaddingLeft() + tickPadding * i;
                rect.top = getPaddingTop();
                rect.right = rect.left + mThumb.getIntrinsicWidth();
                rect.bottom = rect.top + mThumb.getIntrinsicHeight();
                mTickRectList.add(rect);
            }
        }
    }

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

        final int activePosition = (mValue - mValueFrom) / mStepSize;
        final int tickCount = getTickCount();
        final int halfTrackHeight = mTrackHeight >> 1;
        Rect startRect = mTickRectList.get(0);
        Rect centerRect = mTickRectList.get(activePosition);
        Rect endRect = mTickRectList.get(tickCount - 1);
        if (activePosition != 0) {
            mTrackActive.setBounds(startRect.centerX(), startRect.centerY() - halfTrackHeight, centerRect.centerX(), centerRect.centerY() + halfTrackHeight);
            mTrackActive.draw(canvas);
        }
        if (activePosition != tickCount - 1) {
            mTrackInactive.setBounds(centerRect.centerX(), centerRect.centerY() - halfTrackHeight, endRect.centerX(), endRect.centerY() + halfTrackHeight);
            mTrackInactive.draw(canvas);
        }

        for (int i = 0; i < tickCount; i++) {
            Rect rect = mTickRectList.get(i);
            if (i < activePosition) {
                setTickDrawableBound(mTickMarkActive, rect);
                mTickMarkActive.draw(canvas);
            } else if (i > activePosition) {
                setTickDrawableBound(mTickMarkInactive, rect);
                mTickMarkInactive.draw(canvas);
            } else {
                mThumb.setBounds(rect);
                mThumb.draw(canvas);
            }
        }

        if (mLabelCount > 0) {
            drawLabel(canvas);
        }
    }

    private void drawLabel(Canvas canvas) {
        final int tickCount = getTickCount();
        Rect rect;
        String label;
        Paint.FontMetrics fm = mLabelPaint.getFontMetrics();
        final float baseline = (fm.bottom - fm.top) / 2 + (fm.descent - fm.ascent) / 2 - fm.descent;
        for (int i = 0; i < tickCount; i++) {
            label = getLabel(i);
            rect = mTickRectList.get(i);
            if (!TextUtils.isEmpty(label)) {
                float labelWidth = mLabelPaint.measureText(label);
                canvas.drawText(label, rect.centerX() - labelWidth / 2, rect.bottom + mLabelPadding + baseline, mLabelPaint);
            }
        }
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        final int action = event.getActionMasked();
        if (action == MotionEvent.ACTION_DOWN) {
            for (int i = 0; i < getTickCount(); i++) {
                Rect rect = mTickRectList.get(i);
                if (rect.contains((int) event.getX(), (int) event.getY())) {
                    return true;
                }
            }
        } else if (action == MotionEvent.ACTION_UP) {
            if (event.getEventTime() - event.getDownTime() < ViewConfiguration.getTapTimeout()) {
                for (int i = 0; i < getTickCount(); i++) {
                    Rect rect = mTickRectList.get(i);
                    if (rect.contains((int) event.getX(), (int) event.getY())) {
                        mValue = mValueFrom + i * mStepSize;
                        invalidate();
                        break;
                    }
                }
            }
        } else if (action == MotionEvent.ACTION_MOVE) {
            final int x = (int) event.getX();
            int index = 0;
            int centerX = mTickRectList.get(0).centerX();
            for (int i = 1, size = getTickCount(); i < size; i++) {
                Rect rect = mTickRectList.get(i);
                centerX = (centerX + rect.centerX()) >> 1;
                if (x < centerX) {
                    index = i - 1;
                    break;
                }

                if (i == size - 1 && x >= centerX) {
                    index = i;
                    break;
                }
                centerX = rect.centerX();
            }
            final int value = mValueFrom + index * mStepSize;
            if (value != mValue) {
                mValue = value;
                invalidate();
                if (mOnDiscreteValueChangedListener != null) {
                    mOnDiscreteValueChangedListener.onValueChanged(this, value);
                }
            }
        }
        return super.onTouchEvent(event);
    }

    public void setLabelList(List<String> list) {
        mTickLabelList.clear();
        if (list != null) {
            mTickLabelList.addAll(list);
        }
        mLabelCount = mTickLabelList.size();
        requestLayout();
        invalidate();
    }

    public void addLabel(String label) {
        mTickLabelList.add(label);
        mLabelCount = mTickLabelList.size();
        requestLayout();
        invalidate();
    }

    private String getLabel(int position) {
        if (position < mLabelCount) {
            return mTickLabelList.get(position);
        }

        return "";
    }

    public int getTickCount() {
        return (mValueTo - mValueFrom) / mStepSize + 1;
    }

    private void setTickDrawableBound(Drawable drawable, Rect rect) {
        if (drawable.getIntrinsicWidth() > 0 && drawable.getIntrinsicHeight() > 0) {
            int dx = Math.max(rect.width() - drawable.getIntrinsicWidth(), 0) >> 1;
            int dy = Math.max(rect.height() - drawable.getIntrinsicHeight(), 0) >> 1;
            mRect.set(rect);
            mRect.inset(dx, dy);
            drawable.setBounds(mRect);
        } else {
            drawable.setBounds(rect);
        }
    }

    public void setValue(int value) {
        this.mValue = value;
        invalidate();
    }

    public void setOnDiscreteValueChangedListener(OnDiscreteValueChangedListener listener) {
        this.mOnDiscreteValueChangedListener = listener;
    }
}