SeekBar是用来调节参数值的，系统默认的一般都不太适合我们，需要我们自定义，

里面也有一个RxJava背压的具体应用

废话不多说，看图

package com.example.helang.seekbar;import android.content.Context;import android.graphics.Bitmap;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.Matrix;import android.graphics.Paint;import android.graphics.RectF;import android.graphics.drawable.BitmapDrawable;import android.graphics.drawable.Drawable;import android.support.annotation.Nullable;import android.util.AttributeSet;import android.view.MotionEvent;import android.view.View;import java.util.concurrent.TimeUnit;import io.reactivex.Observable;import io.reactivex.ObservableEmitter;import io.reactivex.ObservableOnSubscribe;import io.reactivex.android.schedulers.AndroidSchedulers;import io.reactivex.functions.Consumer;/** * 自定义拖动seekBar */public class CustomSeekBar extends View {    private static final String TAG = "CustomSeekBar";    private static final int radius = 65;//中间圆形进度条的半径    private static final int thumbSize = 200;    private int backgroundLineSize = 10;//背景线的宽度    private int foregroundLineSize = 18;//进度的宽度    private int lineSize;//整条背景线的长度    private float touchY;    private Bitmap thumbBitmap;    private Paint paint;    private Paint circlePaint;//绘制进度条的paint    private RectF backgroundLineRect = new RectF();//背景矩形    private RectF foregroundLineRect = new RectF();//进度矩形    private float currentDegrees = 0;//当前的进度，百分比例，不带百分号    private OnProgressListener onProgressListener;    public void setOnProgressListener(OnProgressListener onProgressListener) {        this.onProgressListener = onProgressListener;    }    public CustomSeekBar(Context context) {        this(context,null);    }    public CustomSeekBar(Context context, @Nullable AttributeSet attrs) {        this(context, attrs,0);    }    public CustomSeekBar(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {        super(context, attrs, defStyleAttr);        initBitmap();        initPaint();    }    /**     * init bitmap     */    private void initBitmap(){        thumbBitmap = drawableToBitmap(thumbSize,getResources().getDrawable(R.drawable.circle));    }    /**     * init paint     */    private void initPaint() {        paint = new Paint();        paint.setStyle(Paint.Style.FILL);        paint.setTextSize(10);        //初始化圆形进度条的Paint        circlePaint = new Paint();        circlePaint.setAntiAlias(true); // 抗锯齿        circlePaint.setDither(true); // 防抖动        circlePaint.setStrokeWidth(10);        circlePaint.setShader(null); // 清除上一次的shader        circlePaint.setStyle(Paint.Style.STROKE); // 设置绘制的圆为空心        circlePaint.setShadowLayer(10, 10, 10, Color.RED);        circlePaint.setColor(Color.BLUE); // 设置圆弧的颜色        circlePaint.setStrokeCap(Paint.Cap.ROUND); // 把每段圆弧改成圆角的    }    @Override    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {        super.onLayout(changed, left, top, right, bottom);    }    @Override    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {        super.onMeasure(widthMeasureSpec, heightMeasureSpec);    }    @Override    protected void onDraw(Canvas canvas) {        super.onDraw(canvas);        drawLine(canvas);        drawThumb(canvas);        drawCircleProgress(canvas);    }    /**     * draw circle     * @param canvas     */    private void drawCircleProgress(Canvas canvas){        RectF oval = new RectF(thumbSize/2-radius, thumbSize/2-radius,                thumbSize/2+radius, thumbSize/2+radius); // 圆的外接正方形        float alphaAngle = currentDegrees * 360.0f / 100 * 1.0f; // 计算每次画圆弧时扫过的角度，这里计算要注意分母要转为float类型，否则alphaAngle永远为0        canvas.drawArc(oval, -90, alphaAngle, false, circlePaint);    }    /**     * draw thumb     * @param canvas     */    private void drawThumb(Canvas canvas){        //添加旋转,Matrix是Bitmap旋转的关键，用于bitmap一些补间动画的操作        canvas.translate((getWidth()-thumbSize)/2,(100-currentDegrees)/100*lineSize);        Matrix matrix  = new Matrix();        matrix.setRotate(currentDegrees*10,thumbSize/2,thumbSize/2);        canvas.drawBitmap(thumbBitmap,matrix,null);//旋转背景    }    /**     * draw lines     * @param canvas     */    private void drawLine(Canvas canvas){        //绘制背景线        backgroundLineRect.set((getWidth()-backgroundLineSize)/2,thumbSize/2,                (getWidth()+backgroundLineSize)/2, getParentHeight()-thumbSize/2);        lineSize = getParentHeight() - thumbSize;//去掉被thumb挡住的一部分长度        paint.setColor(Color.rgb(61,82,89));        canvas.drawRoundRect(backgroundLineRect, backgroundLineSize/2, backgroundLineSize/2, paint);        //绘制进度线        paint.setColor(Color.rgb(90,189,220));//进度线的颜色        foregroundLineRect.set((getWidth()-foregroundLineSize)/2,                (getParentHeight()-thumbSize)*(100-currentDegrees)/100+thumbSize/2,                (getWidth()+foregroundLineSize)/2,getParentHeight()-thumbSize/2);        canvas.drawRoundRect(foregroundLineRect,foregroundLineSize/2,foregroundLineSize/2,paint);    }    /**     * get ParentHeight     * @return     */    private int getParentHeight(){        return getHeight();    }    @Override    public boolean dispatchTouchEvent(MotionEvent event) {        return super.dispatchTouchEvent(event);    }    @Override    public boolean onTouchEvent(MotionEvent event) {        if (!isEnabled())            return true;        switch (event.getAction()) {            case MotionEvent.ACTION_DOWN:                touchY = event.getRawY();//记录开始的Y值                break;            case MotionEvent.ACTION_MOVE:                currentDegrees += (touchY-event.getRawY())*1f/(getParentHeight())*100.0f;//当前进度值（100为满）                if (currentDegrees > 100){//超出去的不计算，默认为100                    currentDegrees = 100;                }                if (currentDegrees<0){//超出去的不计算，默认为0                    currentDegrees = 0;                }                if (observableEmitter != null){//使用背压发送                    observableEmitter.onNext(1);                }else {//直接发送                    sendProgress();                }                touchY = event.getRawY();                invalidate();                break;            case MotionEvent.ACTION_CANCEL:                break;            case MotionEvent.ACTION_UP:                break;        }        return true;    }    private ObservableEmitter
     
       observableEmitter;    /**     *增加背压，防止发射拖动的事件过快,导致内存溢出     */    public void addBackPressure(){        Observable.create(new ObservableOnSubscribe
      
       () {            @Override            public void subscribe(ObservableEmitter
       
         emitter) throws Exception {                observableEmitter = emitter;            }        }).sample(500, TimeUnit.MILLISECONDS)        .observeOn(AndroidSchedulers.mainThread())        .subscribe(new Consumer
        
         () {            @Override            public void accept(Integer integer) throws Exception {                sendProgress();            }        });    }    /**     * 发送进度     */    private void sendProgress(){        if (onProgressListener != null){            onProgressListener.onProgress(currentDegrees);        }    }    /**     * 设置当前进度     * @param currentDegrees     */    public void setCurrentDegrees(float currentDegrees){        this.currentDegrees = currentDegrees;        invalidate();    }    public interface OnProgressListener{        void onProgress(float progress);    }    /**     *  make a drawable to a bitmap     * @param drawable drawable you want convert     * @return converted bitmap     */    private Bitmap drawableToBitmap(int size, Drawable drawable) {        Bitmap bitmap = null;        if (drawable instanceof BitmapDrawable) {            BitmapDrawable bitmapDrawable = (BitmapDrawable) drawable;            bitmap = bitmapDrawable.getBitmap();            if (bitmap != null && bitmap.getHeight() > 0) {                Matrix matrix = new Matrix();                float scaleHeight = size * 1.0f / bitmapDrawable.getIntrinsicHeight();                matrix.postScale(scaleHeight, scaleHeight);                bitmap = Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight(), matrix, true);                return bitmap;            }        }        bitmap = Bitmap.createBitmap(size, size, Bitmap.Config.ARGB_8888);        Canvas canvas = new Canvas(bitmap);        drawable.setBounds(0, 0, canvas.getWidth(), canvas.getHeight());        drawable.draw(canvas);        return bitmap;    }}
        
       
      
     

Demo地址：https://github.com/helang1991/SeekBar

喜欢的就加个Star,谢谢