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Android 自定义View绘制箭头

Android 自定义View绘制箭头

作者: h2coder | 来源:发表于2020-10-06 00:50 被阅读0次

    一般顶部栏的返回键都是让UI切图,其实还可以自定义View绘制,本篇就闲来蛋疼绘制一个箭头返回键吧,有Material Design和微信风格(就是没有中间那条横线)。

    Android 自定义View绘制箭头.png

    原理

    我们观察一下,控件中点,向右一条横线,再从中心点2个45度角的2条线,如果用数学的惯性思维,会想到使用三角函数,计算出2条45度线终点的x,y坐标。但其实Canvas有rotate旋转的API,就不需要那么多麻烦的计算了,2个45度的角,其实就是一个90度的直角,我们可以先画一个直角,然后再旋转45度,就可以了。

    完整代码

    • 自定义属性
    <declare-styleable name="BackArrowView">
            <!-- 箭头颜色 -->
            <attr name="bav_color" format="color" />
            <!-- 箭头线宽 -->
            <attr name="bav_stroke_width" format="integer|float|dimension" />
            <!-- 模式 -->
            <attr name="bav_arrow_style" format="enum">
                <!-- Google Material Design -->
                <enum name="material_design" value="1" />
                <!-- 微信风格 -->
                <enum name="wechat_design" value="2" />
            </attr>
        </declare-styleable>
    
    • Java代码
    public class BackArrowView extends View {
        /**
         * View默认最小宽度
         */
        private static final int DEFAULT_MIN_WIDTH = 100;
        /**
         * Material Design风格
         */
        private static final int ARROW_STYLE_MATERIAL_DESIGN = 1;
        /**
         * 微信风格
         */
        private static final int ARROW_STYLE_WECHAT_DESIGN = 2;
    
        /**
         * 控件宽
         */
        private int mViewWidth;
        /**
         * 控件高
         */
        private int mViewHeight;
        /**
         * 箭头开始的距离
         */
        private float mArrowStartDistance;
        /**
         * 箭头的2个边的长度
         */
        private float mArrowLineLength;
        /**
         * 箭头颜色
         */
        private int mColor;
        /**
         * 箭头粗细
         */
        private float mArrowStrokeWidth;
        /**
         * 风格模式
         */
        private int mArrowStyle;
    
        /**
         * 画笔
         */
        private Paint mPaint;
        /**
         * 箭头Path
         */
        private Path mArrowPath;
    
        public BackArrowView(Context context) {
            this(context, null);
        }
    
        public BackArrowView(Context context, @Nullable AttributeSet attrs) {
            this(context, attrs, 0);
        }
    
        public BackArrowView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
            super(context, attrs, defStyleAttr);
            init(context, attrs, defStyleAttr);
        }
    
        private void init(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
            initAttr(context, attrs, defStyleAttr);
            mPaint = new Paint();
            mPaint.setColor(mColor);
            //使用Path必须使用STROKE,使用FILL是画不了的
            mPaint.setStyle(Paint.Style.STROKE);
            mPaint.setAntiAlias(true);
            mPaint.setStrokeWidth(mArrowStrokeWidth);
            //设置拐角形状为圆形,3条线相接处则不会有缝隙了
            mPaint.setStrokeJoin(Paint.Join.ROUND);
        }
    
        private void initAttr(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
            TypedArray array = context.obtainStyledAttributes(attrs, R.styleable.BackArrowView, defStyleAttr, 0);
            mColor = array.getColor(R.styleable.BackArrowView_bav_color, Color.argb(255, 0, 0, 0));
            mArrowStrokeWidth = array.getDimension(R.styleable.BackArrowView_bav_stroke_width, dip2px(context, 2f));
            mArrowStyle = array.getInt(R.styleable.BackArrowView_bav_arrow_style, ARROW_STYLE_MATERIAL_DESIGN);
            array.recycle();
        }
    
        @Override
        protected void onSizeChanged(int w, int h, int oldw, int oldh) {
            super.onSizeChanged(w, h, oldw, oldh);
            mViewWidth = w;
            mViewHeight = h;
            //计算半径
            float radius = Math.min(mViewWidth, mViewHeight) / 2f;
            //计算箭头起始位置
            if (mArrowStyle == ARROW_STYLE_MATERIAL_DESIGN) {
                mArrowStartDistance = radius / 3f;
            } else if (mArrowStyle == ARROW_STYLE_WECHAT_DESIGN) {
                mArrowStartDistance = radius / 4f;
            }
            //计算箭头长度
            mArrowLineLength = radius * 0.63f;
        }
    
        @Override
        protected void onDraw(Canvas canvas) {
            super.onDraw(canvas);
            //将画布中心移动到中心点偏左位置
            canvas.translate((mViewWidth / 2f) - mArrowStartDistance, mViewHeight / 2);
            //将画布旋转45度,让后面画的直角旋转
            canvas.rotate(45);
            if (mArrowPath == null) {
                mArrowPath = new Path();
            }
            mArrowPath.reset();
            //画第一条线
            mArrowPath.lineTo(0, -mArrowLineLength);
            //画第二条线
            mArrowPath.moveTo(0, 0);
            mArrowPath.lineTo(mArrowLineLength, 0);
            //Google Material Design风格才有中间的线
            if (mArrowStyle == ARROW_STYLE_MATERIAL_DESIGN) {
                //画中间的线
                mArrowPath.moveTo(0, 0);
                mArrowPath.lineTo(mArrowLineLength, -mArrowLineLength);
            }
            //闭合路径
            mArrowPath.close();
            //画路径
            canvas.drawPath(mArrowPath, mPaint);
        }
    
        @Override
        protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
            super.onMeasure(widthMeasureSpec, heightMeasureSpec);
            setMeasuredDimension(handleMeasure(widthMeasureSpec), handleMeasure(heightMeasureSpec));
        }
    
        /**
         * 处理MeasureSpec
         */
        private int handleMeasure(int measureSpec) {
            int result = DEFAULT_MIN_WIDTH;
            int specMode = MeasureSpec.getMode(measureSpec);
            int specSize = MeasureSpec.getSize(measureSpec);
            if (specMode == MeasureSpec.EXACTLY) {
                result = specSize;
            } else {
                //处理wrap_content的情况
                if (specMode == MeasureSpec.AT_MOST) {
                    result = Math.min(result, specSize);
                }
            }
            return result;
        }
    
        public static int dip2px(Context context, float dipValue) {
            final float scale = context.getResources().getDisplayMetrics().density;
            return (int) (dipValue * scale + 0.5f);
        }
    }
    
    • 简单使用
    <com.zh.cavas.sample.widget.BackArrowView
        android:id="@+id/back_arrow"
        android:layout_width="40dp"
        android:layout_height="40dp"
        android:layout_marginTop="20dp"
        app:bav_arrow_style="wechat_design"
        app:bav_color="@android:color/black"
        app:bav_stroke_width="1.5dp" />
    
    <com.zh.cavas.sample.widget.BackArrowView
        android:id="@+id/back_arrow2"
        android:layout_width="40dp"
        android:layout_height="40dp"
        android:layout_marginTop="20dp"
        app:bav_arrow_style="material_design"
        app:bav_color="@android:color/black"
        app:bav_stroke_width="1.5dp" />
    

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