Android中自定義常用的三個對象解析（Paint,Color,Canvas）

Paint,Color,Canvas

Paint:畫筆對象，畫圖用的“筆”
Color:顏色，相當於調料
Canvas:畫布，現實中的紙板

Paint 畫筆

常用的方法就是設置和獲取到畫筆的樣式：

paint.setStyle();   設置畫筆的風格，空心的或者是實心的
paint.setColor();   設置畫筆的顏色
paint.setStrokeWidth(); 設置邊框線的寬度
paint.setAlpha();   設置畫筆的Alpha值
paint.setAntiAlias();       設置畫筆的鋸齒效果
paint.setTextSize();        設置字體的大小
paint.getAlpha();       獲取到畫筆的Alpha值
paint.getColor();       獲取到畫筆的顏色
paint.getTextBounds();  獲取到最小的能包容字體的邊框
。。。。。。。

Color 顏色

通過Color.顏色名 ,來獲取到想要的顏色。
Color裡面設置了許多常用的顏色枚舉值，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;

同樣，也可以自定義想要的顏色：調用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 畫布，可以繪制常見的圖形，比如圓，直線，矩形

繪制直線：canvas.drawLine();

    /**
     * Draw a line segment with the specified start and stop x,y coordinates,
     * using the specified paint.
     *
     * 

Note that since a line is always "framed", the Style is ignored in the paint.

Degenerate lines (length is 0) will not be drawn.

繪制圓：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)

繪制矩形：;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)

繪制圖片：canvas.drawBitmap();

     /**
     * Draw the specified bitmap, with its top/left corner at (x,y), using
     * the specified paint, transformed by the current matrix.
     *
     * 

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. * *

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)

繪制文本：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)

繪制圓弧：canvas.drawArc();

    /**
     * 

Draw the specified arc, which will be scaled to fit inside the * specified oval.

If the start angle is negative or >= 360, the start angle is treated * as start angle modulo 360.

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

The arc is drawn clockwise. An angle of 0 degrees correspond to the * geometric angle of 0 degrees (3 o'clock on a watch.)

。。。。。。。

小結

自定義view的時候一般會重寫onDraw()方法，畫圖時必要的三要素：Color,paint,canvas

設置畫筆的樣式

設置顏色

在畫布上作圖