Android中自定义常用的三个对象解析（Paint,Color,Canvas）

Paint,Color,Canvas

Paint:画笔对象，画图用的“笔”
Color:颜色，相当于调料
Canvas:画布，现实中的纸板

Paint 画笔

常用的方法就是设置和获取到画笔的样式：

paint.setStyle();   设置画笔的风格，空心的或者是实心的
paint.setColor();   设置画笔的颜色
paint.setStrokeWidth(); 设置边框线的宽度
paint.setAlpha();   设置画笔的Alpha值
paint.setAntiAlias();       设置画笔的锯齿效果
paint.setTextSize();        设置字体的大小
paint.getAlpha();       获取到画笔的Alpha值
paint.getColor();       获取到画笔的颜色
paint.getTextBounds();  获取到最小的能包容字体的边框
。。。。。。。

Color 颜色

通过Color.颜色名 ,来获取到想要的颜色。
Color里面设置了许多常用的颜色枚举值，比如：

    @ColorInt public static final int BLACK       = 0xFF000000;
    @ColorInt public static final int DKGRAY      = 0xFF444444;
    @ColorInt public static final int GRAY        = 0xFF888888;
    @ColorInt public static final int LTGRAY      = 0xFFCCCCCC;
    @ColorInt public static final int WHITE       = 0xFFFFFFFF;
    @ColorInt public static final int RED         = 0xFFFF0000;
    @ColorInt public static final int GREEN       = 0xFF00FF00;
    @ColorInt public static final int BLUE        = 0xFF0000FF;
    @ColorInt public static final int YELLOW      = 0xFFFFFF00;
    @ColorInt public static final int CYAN        = 0xFF00FFFF;
    @ColorInt public static final int MAGENTA     = 0xFFFF00FF;
    @ColorInt public static final int TRANSPARENT = 0;

同样，也可以自定义想要的颜色：调用Color.argb()

  /**
     * Return a color-int from alpha, red, green, blue components.
     * These component values should be [0..255], but there is no
     * range check performed, so if they are out of range, the
     * returned color is undefined.
     * @param alpha Alpha component [0..255] of the color
     * @param red   Red component [0..255] of the color
     * @param green Green component [0..255] of the color
     * @param blue  Blue component [0..255] of the color
     */
    @ColorInt
    public static int argb(int alpha, int red, int green, int blue) {
        return (alpha << 24) | (red << 16) | (green << 8) | blue;
    }

Canvas 画布，可以绘制常见的图形，比如圆，直线，矩形

绘制直线：canvas.drawLine();

    /**
     * Draw a line segment with the specified start and stop x,y coordinates,
     * using the specified paint.
     *
     * <p>Note that since a line is always "framed", the Style is ignored in the paint.</p>
     *
     * <p>Degenerate lines (length is 0) will not be drawn.</p>
     *
     * @param startX The x-coordinate of the start point of the line
     * @param startY The y-coordinate of the start point of the line
     * @param paint  The paint used to draw the line
     */
    public void **drawLine**(float startX, float startY, float stopX, float stopY,
            @NonNull Paint paint)

绘制圆：canvas.drawCircle();

    /**
     * Draw the specified circle using the specified paint. If radius is <= 0,
     * then nothing will be drawn. The circle will be filled or framed based
     * on the Style in the paint.
     *
     * @param cx     The x-coordinate of the center of the cirle to be drawn
     * @param cy     The y-coordinate of the center of the cirle to be drawn
     * @param radius The radius of the cirle to be drawn
     * @param paint  The paint used to draw the circle
     */
    public void **drawCircle**(float cx, float cy, float radius, @NonNull Paint paint)

绘制矩形：;canvas.drawRect();

    /**
     * Draw the specified Rect using the specified paint. The rectangle will
     * be filled or framed based on the Style in the paint.
     *
     * @param left   The left side of the rectangle to be drawn
     * @param top    The top side of the rectangle to be drawn
     * @param right  The right side of the rectangle to be drawn
     * @param bottom The bottom side of the rectangle to be drawn
     * @param paint  The paint used to draw the rect
     */
    public void **drawRect**(float left, float top, float right, float bottom, @NonNull Paint paint)

绘制图片：canvas.drawBitmap();

     /**
     * Draw the specified bitmap, with its top/left corner at (x,y), using
     * the specified paint, transformed by the current matrix.
     *
     * <p>Note: if the paint contains a maskfilter that generates a mask which
     * extends beyond the bitmap‘s original width/height (e.g. BlurMaskFilter),
     * then the bitmap will be drawn as if it were in a Shader with CLAMP mode.
     * Thus the color outside of the original width/height will be the edge
     * color replicated.
     *
     * <p>If the bitmap and canvas have different densities, this function
     * will take care of automatically scaling the bitmap to draw at the
     * same density as the canvas.
     *
     * @param bitmap The bitmap to be drawn
     * @param left   The position of the left side of the bitmap being drawn
     * @param top    The position of the top side of the bitmap being drawn
     * @param paint  The paint used to draw the bitmap (may be null)
     */
    public void **drawBitmap**(@NonNull Bitmap bitmap, float left, float top, @Nullable Paint paint) {
        throwIfCannotDraw(bitmap)

绘制文本：canvas.drawText();

    /**
     * Draw the text, with origin at (x,y), using the specified paint. The
     * origin is interpreted based on the Align setting in the paint.
     *
     * @param text  The text to be drawn
     * @param x     The x-coordinate of the origin of the text being drawn
     * @param y     The y-coordinate of the baseline of the text being drawn
     * @param paint The paint used for the text (e.g. color, size, style)
     */
    public void **drawText**(@NonNull String text, float x, float y, @NonNull Paint paint)

绘制圆弧：canvas.drawArc();

    /**
     * <p>Draw the specified arc, which will be scaled to fit inside the
     * specified oval.</p>
     *
     * <p>If the start angle is negative or >= 360, the start angle is treated
     * as start angle modulo 360.</p>
     *
     * <p>If the sweep angle is >= 360, then the oval is drawn
     * completely. Note that this differs slightly from SkPath::arcTo, which
     * treats the sweep angle modulo 360. If the sweep angle is negative,
     * the sweep angle is treated as sweep angle modulo 360</p>
     *
     * <p>The arc is drawn clockwise. An angle of 0 degrees correspond to the
     * geometric angle of 0 degrees (3 o‘clock on a watch.)</p>
     *
     * @param oval       The bounds of oval used to define the shape and size
     *                   of the arc
     * @param startAngle Starting angle (in degrees) where the arc begins
     * @param sweepAngle Sweep angle (in degrees) measured clockwise
     * @param useCenter If true, include the center of the oval in the arc, and
                        close it if it is being stroked. This will draw a wedge
     * @param paint      The paint used to draw the arc
     */
    public void **drawArc**(@NonNull RectF oval, float startAngle, float sweepAngle, boolean useCenter,
            @NonNull Paint paint)

。。。。。。。

小结

自定义view的时候一般会重写onDraw()方法，画图时必要的三要素：Color,paint,canvas

设置画笔的样式

设置颜色

在画布上作图