android自定义view用path画一个长方形

这次主要是练习一下Android的自定义view和path的相关使用，所以做了一个简单的demo：自定义一个view，并用path在上面画一个可以动态改变圆角大小的长方形。

自定义相关属性

自定义view首先需要在values文件夹下建一个attrs文件，并在其中定义view的相关属性，如下：

<resources>
    <declare-styleable name="CustomView">
        <attr name="round_position">
            <flag name="left-top" value="0x1"></flag>
            <flag name="right-top" value="0x4"></flag>
            <flag name="left-bottom" value="0x2"></flag>
            <flag name="right-bottom" value="0x8"></flag>
        </attr>
        <attr name="round_radius" format="dimension"></attr>
    </declare-styleable>
</resources>

其中round_position指的是圆角的位置，这里属性类型定为flag（位或运算）这样就可以在布局中同时使用多个属性了，类似于EditText中定义文字样式：android:textStyle="bold|italic";round_radius指圆角大小，类型为dimension。

自定义view类

新建一个类继承View，如下：

public class CustomView extends View {
    private Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
    private Path path;
    private int color = Color.GREEN;
    private final int LEFT_TOP = 0x1;
    private final int LEFT_BOTTOM = 0x2;
    private final int RIGHT_TOP = 0x4;
    private final int RIGHT_BOTTOM = 0x8;
    private boolean drawLeftTop;
    private boolean drawLeftBottom;
    private boolean drawRightTop;
    private boolean drawRightBottom;
    private float radius;

    public CustomView(Context context) {
        super(context);
        initDraw();
    }

    public CustomView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.CustomView);
        int position = typedArray.getInt(R.styleable.CustomView_round_position, 0);
        radius = typedArray.getDimension(R.styleable.CustomView_round_radius, 0);
        drawLeftTop = (position & LEFT_TOP) == LEFT_TOP;
        drawLeftBottom = (position & LEFT_BOTTOM) == LEFT_BOTTOM;
        drawRightTop = (position & RIGHT_TOP) == RIGHT_TOP;
        drawRightBottom = (position & RIGHT_BOTTOM) == RIGHT_BOTTOM;
        typedArray.recycle();
        initDraw();
    }

    public CustomView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        initDraw();
    }

    private void initDraw() {
        path = new Path();
        paint.setColor(Color.GREEN);
        paint.setAntiAlias(true);
        paint.setStrokeWidth((float) 5);
        paint.setStyle(Paint.Style.STROKE);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        path.reset();//这里很重要，如果不写这一行，则每次重绘view后先前绘制的还会存在
        path.moveTo(radius, 0);
        if (drawRightTop) {
            path.lineTo(getWidth() - radius, 0);
//            path.cubicTo(radius + getWidth() / 3, 0, radius + getWidth() / 3 * 2, 0, getWidth() - radius, 0);
            path.cubicTo(getWidth() - radius / 2, 0, getWidth(), radius / 2, getWidth(), radius);
        } else {
            path.lineTo(getWidth(), 0);
//            path.cubicTo(radius + getWidth() / 3, 0, radius + getWidth() / 3 * 2, 0, getWidth(), 0);
        }
        path.lineTo(getWidth(), getHeight() - radius);
//        path.cubicTo(getWidth(), radius + getHeight() / 3, getWidth(), radius + getHeight() / 3 * 2, getWidth(), getHeight() - radius);
        if (drawRightBottom) {
            path.cubicTo(getWidth(), getHeight() - radius / 2, getWidth() - radius / 2, getHeight(), getWidth() - radius, getHeight());
        } else {
            path.lineTo(getWidth(), getHeight());
        }
        path.lineTo(radius, getHeight());
        if (drawLeftBottom) {
            path.cubicTo(radius / 2, getHeight(), 0, getHeight() - radius / 2, 0, getHeight() - radius);
        } else {
            path.lineTo(0, getHeight());
        }
        path.lineTo(0, radius);
        if (drawLeftTop) {
            path.cubicTo(0, radius / 2, radius / 2, 0, radius, 0);
        } else {
            path.lineTo(0, 0);
            path.lineTo(radius, 0);
        }
        canvas.drawPath(path, paint);
        super.onDraw(canvas);
    }

    public void setRadius(float radius) {
        this.radius = radius;
    }

    public void refreshView() {
        invalidate();
    }
}

这里使用了path和贝塞尔曲线的绘制方法来绘制可动态调整圆角大小的长方形，注意每次重绘时要先调用path.reset()清除之前绘制的path，然后再绘制新的path，不然旧的path还会一直存在。

布局中使用自定义view

<wjc.myrecyclerview.CustomView
        android:id="@+id/custom_view"
        android:layout_width="200dp"
        android:layout_height="200dp"
        android:layout_margin="100dp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:round_position="left-bottom|right-bottom|right-top|left-top" />

这样就完成了一个简单的自定义可调整圆角的长方形，在MainActivity中进行动态控制：

view.setRadius(progress);
view.refreshView();

实现的最终效果