效果图：

问题

如何线性颜色变化？

  Shader mShader = new LinearGradient(pointX - raduis, pointY, pointX + raduis, pointY,                new int[]{0xFF445EED, 0xFF072AE9, 0xFF0625CE}, null, Shader.TileMode.CLAMP);

完整的自定义View

public class SpeedControlView extends View implements Runnable {    //画笔    private Paint mPaint, textPaint, speedAreaPaint;    private Context mContext;    //屏幕宽高    private int screenWidth, screenHeight;    //仪表盘圆的半径    private float raduis, sRaduis;    //圆心    private int pointX, pointY;    //文字的偏移量    private float textScale;    //速度指针变化的位置    private float linePointerX, linePointerY;    //速度    private int speed;    //速度范围的2个扇形外切矩形    private RectF speedRectF, speedRectFInner;    //速度控制模式  1 加速  2 减速  3 手刹    private int type;
    // 速度文字 绘制的XY坐标    private int baseX, baseY;
    //屏幕密度    private float mDensityDpi;
    //设置速度控制模式    public void setType(int type) {        this.type = type;    }
    //开始重绘    private boolean start = true;
    public void setStart(boolean start) {        this.start = start;    }
    // 设置速度 并重绘视图    public void setSpeed(int speed) {        this.speed = speed;        if (speed > 0) {            postInvalidate();        }    }

    public SpeedControlView(Context context) {        this(context, null);    }
    public SpeedControlView(Context context, AttributeSet attrs) {        this(context, attrs, 0);    }
    public SpeedControlView(Context context, AttributeSet attrs, int defStyleAttr) {        super(context, attrs, defStyleAttr);        mContext = context;
        //获取屏幕宽高//        screenWidth = ((Activity) context).getWindowManager().getDefaultDisplay().getWidth();//        screenHeight = ((Activity) context).getWindowManager().getDefaultDisplay().getHeight();
        //获取屏幕宽高 和 屏幕密度dpi        DisplayMetrics displayMetrics = getResources().getDisplayMetrics();        screenWidth = displayMetrics.widthPixels;        screenHeight = displayMetrics.heightPixels;        mDensityDpi = displayMetrics.densityDpi / 320;  //320为我的测试机dpi密度，以次绘制视图        //关闭硬件加速        setLayerType(LAYER_TYPE_SOFTWARE, null);        //设置抗锯齿        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);        mPaint.setAntiAlias(true);        //设置画笔样式        mPaint.setStyle(Paint.Style.FILL);        mPaint.setStrokeWidth(5 * mDensityDpi);
        //初始化  圆心左边 和 半径        raduis = screenWidth / 3;        pointX = pointY = screenWidth / 2;//        pointY = screenHeight / 4;
        //设置抗锯齿        textPaint = new Paint(Paint.ANTI_ALIAS_FLAG);        textPaint.setAntiAlias(true);        //设置画笔颜色        textPaint.setColor(Color.WHITE);        // 获取字体并设置画笔字体        Typeface typeface = Typeface.createFromAsset(mContext.getAssets(), "kt.ttf");        textPaint.setTypeface(typeface);        //设置抗锯齿        speedAreaPaint = new Paint(Paint.ANTI_ALIAS_FLAG);        speedAreaPaint.setAntiAlias(true);        //设置画笔样式        speedAreaPaint.setStyle(Paint.Style.FILL);        // 设置速度范围扇形的渐变颜色        Shader mShader = new LinearGradient(pointX - raduis, pointY, pointX + raduis, pointY,                new int[]{0xFF445EED, 0xFF072AE9, 0xFF0625CE}, null, Shader.TileMode.CLAMP);        speedAreaPaint.setShader(mShader);        // 初始化速度范围的2个扇形外切矩形        speedRectF = new RectF(pointX - raduis + 10 * mDensityDpi, pointY - raduis + 10 * mDensityDpi,                pointX + raduis - 10 * mDensityDpi, pointY + raduis - 10 * mDensityDpi);        speedRectFInner = new RectF(pointX - raduis / 2, pointY - raduis / 2,                pointX + raduis / 2, pointY + raduis / 2);    }
    @Override    protected void onDraw(Canvas canvas) {        super.onDraw(canvas);        canvas.drawColor(Color.YELLOW);
        //绘制外层圆，两个外圈，两个内圈        drawCicle(canvas);
        //绘制速度范围扇形区域        speedAreaPaint.setColor(0x7E3F51B5);        drawSpeedArea(canvas);
        //变换画笔颜色 绘制刻度        mPaint.setColor(0xBF3F6AB5);        drawScale(canvas);
        //变换画笔颜色 绘制速度标识文字        textPaint.setTextSize(25 * mDensityDpi);        mPaint.setColor(Color.WHITE);        sRaduis = raduis - 50 * mDensityDpi;        textScale = Math.abs(textPaint.descent() + textPaint.ascent()) / 2;        Log.e("textScale", textScale + "");
        drawText(canvas);
        //绘制中间文字内容        drawCenter(canvas);    }
    /**     * 绘制外层圆     */    private void drawCicle(Canvas canvas) {        mPaint.setStyle(Paint.Style.FILL);        mPaint.setColor(0xFF343434);        canvas.drawCircle(pointX, pointY, raduis, mPaint);
        //外圈2个圆        mPaint.setStyle(Paint.Style.STROKE);        mPaint.setColor(0xBF3F6AB5);        mPaint.setStrokeWidth(4 * mDensityDpi);        canvas.drawCircle(pointX, pointY, raduis, mPaint);        mPaint.setStrokeWidth(3 * mDensityDpi);        canvas.drawCircle(pointX, pointY, raduis - 10 * mDensityDpi, mPaint);
        //内圈2个圆        mPaint.setStrokeWidth(5 * mDensityDpi);        mPaint.setColor(0xE73F51B5);        canvas.drawCircle(pointX, pointY, raduis / 2, mPaint);        mPaint.setColor(0x7E3F51B5);        canvas.drawCircle(pointX, pointY, raduis / 2 + 5 * mDensityDpi, mPaint);        mPaint.setStrokeWidth(3 * mDensityDpi);
    }
    /**     * 绘制速度区域扇形     */    private void drawSpeedArea(Canvas canvas) {        int degree;        if (speed < 210) {            degree = speed * 36 / 30;        } else {            degree = 210 * 36 / 30;        }
        canvas.drawArc(speedRectF, 144, degree, true, speedAreaPaint);
        // TODO: 2016/5/12        //不显示中间的内圈的扇形区域        mPaint.setColor(0xFF343434);        mPaint.setStyle(Paint.Style.FILL);        canvas.drawArc(speedRectFInner, 144, degree, true, mPaint);        mPaint.setStyle(Paint.Style.STROKE);    }

    /**     * 绘制刻度     */    private void drawScale(Canvas canvas) {        for (int i = 0; i < 60; i++) {            if (i % 6 == 0) {                canvas.drawLine(pointX - raduis + 10 * mDensityDpi, pointY, pointX - raduis + 50 * mDensityDpi, pointY, mPaint);            } else {                canvas.drawLine(pointX - raduis + 10 * mDensityDpi, pointY, pointX - raduis + 30 * mDensityDpi, pointY, mPaint);            }            canvas.rotate(6, pointX, pointY);        }    }
    /**     * 绘制速度标识文字     */    private void drawText(Canvas canvas) {//        canvas.save();//        canvas.rotate(-36, pointX, pointY);        for (int i = 0; i < 8; i++) {            int value = 30 * i;            String TEXT = String.valueOf(value);            switch (value) {                case 0:                    // 计算Baseline绘制的起点X轴坐标                    baseX = (int) (pointX - sRaduis * Math.cos(Math.PI / 5) + textPaint.measureText(TEXT) / 2 + textScale / 2);                    // 计算Baseline绘制的Y坐标                    baseY = (int) (pointY + sRaduis * Math.sin(Math.PI / 5) + textScale / 2);                    break;                case 30:                    baseX = (int) (pointX - raduis + 50 * mDensityDpi + textPaint.measureText(TEXT) / 2);                    baseY = (int) (pointY + textScale);                    break;                case 60:                    baseX = (int) (pointX - sRaduis * Math.cos(Math.PI / 5) + textScale);                    baseY = (int) (pointY - sRaduis * Math.sin(Math.PI / 5) + textScale * 2);                    break;                case 90:                    baseX = (int) (pointX - sRaduis * Math.cos(2 * Math.PI / 5) - textScale / 2);                    baseY = (int) (pointY - sRaduis * Math.sin(2 * Math.PI / 5) + 2 * textScale);                    break;                case 120:                    baseX = (int) (pointX + sRaduis * Math.sin(Math.PI / 10) - textPaint.measureText(TEXT) / 2);                    baseY = (int) (pointY - sRaduis * Math.cos(Math.PI / 10) + 2 * textScale);                    break;                case 150:                    baseX = (int) (pointX + sRaduis * Math.cos(Math.PI / 5) - textPaint.measureText(TEXT) - textScale / 2);                    baseY = (int) (pointY - sRaduis * Math.sin(Math.PI / 5) + textScale * 2);                    break;                case 180:                    baseX = (int) (pointX + sRaduis - textPaint.measureText(TEXT) - textScale / 2);                    baseY = (int) (pointY + textScale);                    break;                case 210:                    baseX = (int) (pointX + sRaduis * Math.cos(Math.PI / 5) - textPaint.measureText(TEXT) - textScale / 2);                    baseY = (int) (pointY + sRaduis * Math.sin(Math.PI / 5) - textScale / 2);                    break;            }//            baseX = (int) (pointX - raduis + 50 * mDensityDpi + textPaint.measureText(TEXT) / 2);//            baseY = (int) (pointY + textScale);            canvas.drawText(TEXT, baseX, baseY, textPaint);//            canvas.rotate(36, pointX, pointY);        }//        canvas.restore();    }
    /**     * 绘制中间文字内容     */    private void drawCenter(Canvas canvas) {        //速度        textPaint.setTextSize(60 * mDensityDpi);        float tw = textPaint.measureText(String.valueOf(speed));        baseX = (int) (pointX - tw / 2);        baseY = (int) (pointY + Math.abs(textPaint.descent() + textPaint.ascent()) / 4);        canvas.drawText(String.valueOf(speed), baseX, baseY, textPaint);
        //单位        textPaint.setTextSize(20 * mDensityDpi);        tw = textPaint.measureText("km/h");        baseX = (int) (pointX - tw / 2);        baseY = (int) (pointY + raduis / 4 + Math.abs(textPaint.descent() + textPaint.ascent()) / 4);        canvas.drawText("km/h", baseX, baseY, textPaint);    }

    @Override    public void run() {        int speedChange;        while (start) {            switch (type) {                case 1://油门                    speedChange = 3;                    break;                case 2://刹车                    speedChange = -5;                    break;                case 3://手刹                    speed = 0;                default:                    speedChange = -1;                    break;            }            speed += speedChange;            if (speed < 1) {                speed = 0;            }            try {                Thread.sleep(50);                setSpeed(speed);            } catch (InterruptedException e) {                e.printStackTrace();                break;            }        }    }}

调用：

@Overrideprotected void onResume() {    super.onResume();    if (speedControlView != null) {        speedControlView.setSpeed(0);        speedControlView.setStart(true);    }    new Thread(speedControlView).start();}
@Overrideprotected void onStop() {    super.onStop();    if (speedControlView != null) {        speedControlView.setSpeed(0);        speedControlView.setStart(false);    }}

具体的实现过程看代码，到这里就结束啦。

Android仿汽车速度仪表盘

问题

完整的自定义View