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作者：kqw攻城狮
出处：个人站 | CSDN

Android自定义View绘图基础

View的测量

控件的测量可以说是固定写法，原生的View只支持EXACTLY的测量模式，我们自定义的控件可以重写onMeasure方法

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    setMeasuredDimension(getMeasuredSize(widthMeasureSpec), getMeasuredSize(heightMeasureSpec));
}

onMeasure方法给我们返回的widthMeasureSpec和heightMeasureSpec，我们并不能直接拿过来使用，需要使用MeasureSpec类进行解析，来获取测量后的具体值。
首先需要获取测量模式

MeasureSpec.getMode(measureSpec)

getMode方法返回是测量的模式，有以下3种类型：
- MeasureSpec.EXACTLY : 精确值模式（指定值/match_parent）
- MeasureSpec.AT_MOST : 最大值模式（wrap_content）
- MeasureSpec.UNSPECIFIED : 不指定大小的测量模式（一般用不上）

获取到了测量模式以后，获取测量后的大小

MeasureSpec.getSize(measureSpec)

根据上面的意思，可以封装我们的getMeasuredSize方法

// 默认大小
private static final int DEFAULT_SIZE = 200;

/**
 * 获取测量后的大小
 *
 * @param measureSpec measureSpec
 * @return measuredSize
 */
private int getMeasuredSize(int measureSpec) {
    switch (MeasureSpec.getMode(measureSpec)) {
        case MeasureSpec.EXACTLY: // 精确值模式（指定值/match_parent）
            Log.i(TAG, "getMeasuredSize: 精确值模式");
            return MeasureSpec.getSize(measureSpec);
        case MeasureSpec.AT_MOST: // 最大值模式（wrap_content）
            Log.i(TAG, "getMeasuredSize: 最大值模式");
            return Math.min(DEFAULT_SIZE, MeasureSpec.getSize(measureSpec));
        case MeasureSpec.UNSPECIFIED: // 不指定大小的测量模式
            return DEFAULT_SIZE;
        default:
            return DEFAULT_SIZE;
    }
}

现在我们自定义的View就支持自定义的大小了，包括match_parent、wrap_content、具体值。

View的绘制

画笔属性

创建画笔

Paint paint = new Paint();

Shader

BitmapShader, ComposeShader, LinearGradient, RadialGradient, SweepGradient

点

/**
 * Helper for drawPoints() for drawing a single point.
 */
public void drawPoint(float x, float y, @NonNull Paint paint)

canvas.drawPoint(10, 10, paint);

直线

绘制一条直线

/**
 * 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)

绘制多条直线

public void drawLines(@Size(multiple=4) @NonNull float[] pts, @NonNull Paint paint)

矩形

/**
 * 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)

canvas.drawRect(100, 100, 200, 200, paint);

圆角矩形

/**
 * Draw the specified round-rect using the specified paint. The roundrect
 * will be filled or framed based on the Style in the paint.
 *
 * @param rx    The x-radius of the oval used to round the corners
 * @param ry    The y-radius of the oval used to round the corners
 * @param paint The paint used to draw the roundRect
 */
public void drawRoundRect(float left, float top, float right, float bottom, float rx, float ry, @NonNull Paint paint)

canvas.drawRoundRect(100, 100, 200, 200, 20, 20, paint);

圆

/**
 * 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)

// 画圆
canvas.drawCircle(200, 200, 100, paint);

扇形

/**
 * <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 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(float left, float top, float right, float bottom, float startAngle, float sweepAngle, boolean useCenter, @NonNull Paint paint)

// 扇形 起始角度0度 旋转角度120度
canvas.drawArc(100, 100, 200, 200, 0, 120, true, paint);

弧形

扇形通过调整属性，可以实现弧形的效果，首先画笔设置成空心

// 空心
paint.setStyle(Paint.Style.STROKE);

设置画扇形的useCenter参数为false

// 弧形 起始角度0度 旋转角度120度
canvas.drawArc(100, 100, 200, 200, 0, 120, false, paint);

椭圆

/**
 * Draw the specified oval using the specified paint. The oval will be
 * filled or framed based on the Style in the paint.
 */
public void drawOval(float left, float top, float right, float bottom, @NonNull Paint paint)

// 椭圆
canvas.drawOval(100, 100, 500, 300, paint);

文字

/**
 * 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)

// 文字
paint.setTextSize(30);
paint.setColor(Color.BLACK);
canvas.drawText("KongQingwei", 100, 100, paint);

在指定位置显示每个字符

/**
 * Draw the text in the array, with each character's origin specified by
 * the pos array.
 *
 * @param text  The text to be drawn
 * @param pos   Array of [x,y] positions, used to position each character
 * @param paint The paint used for the text (e.g. color, size, style)
 *
 * @deprecated This method does not support glyph composition and decomposition and
 * should therefore not be used to render complex scripts. It also doesn't
 * handle supplementary characters (eg emoji).
 */
@Deprecated
public void drawPosText(@NonNull String text, @NonNull @Size(multiple=2) float[] pos, @NonNull Paint paint)

canvas.drawPosText("KongQingwei", new float[]{
        30,30,
        60,60,
        90,90,
        120,120,
        150,150,
        180,180,
        210,210,
        240,240,
        270,270,
        300,300,
        330,330
}, paint);

绘制路径

可以自定义画出想要的任意图形

五角星

/**
 * Draw the specified path using the specified paint. The path will be
 * filled or framed based on the Style in the paint.
 *
 * @param path  The path to be drawn
 * @param paint The paint used to draw the path
 */
public void drawPath(@NonNull Path path, @NonNull Paint paint)

Path path = new Path();
path.moveTo(0,100);
path.lineTo(250,300);
path.lineTo(150,0);
path.lineTo(50,300);
path.lineTo(300,100);
path.lineTo(0,100);
canvas.drawPath(path,paint);

空心

paint.setStyle(Paint.Style.STROKE);

图形裁剪

以上面的实心五角星为例，以五角星的中心为圆心，裁剪出一个半径为100的圆形

/**
    * Modify the current clip with the specified path.
 *
 * @param path The path to operate on the current clip
 * @param op   How the clip is modified
 * @return     true if the resulting is non-empty
 */
public boolean clipPath(@NonNull Path path, @NonNull Region.Op op)

// 裁剪一个圆形
Path path = new Path();
path.reset();
path.addCircle(150, 150, 100, Path.Direction.CCW);
canvas.clipPath(path, Region.Op.INTERSECT);
// canvas.save();
// 画五角星
path.reset();
path.moveTo(0,100);
path.lineTo(250,300);
path.lineTo(150,0);
path.lineTo(50,300);
path.lineTo(300,100);
path.lineTo(0,100);
canvas.drawPath(path,paint);

Region.Op	描述	样式
INTERSECT	裁剪内部交集
DIFFERENCE	外部