自定义View之描边、便签、贴纸效果

效果图：

一个边框，角落附带两条斜线，形成了类似贴纸的效果。

完整代码如下：

import android.content.Context;
import android.content.res.Resources.Theme;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Paint.Style;
import android.os.Build.VERSION_CODES;
import android.support.annotation.AttrRes;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.annotation.RequiresApi;
import android.support.annotation.StyleRes;
import android.util.AttributeSet;
import android.util.TypedValue;
import android.widget.RelativeLayout;

/**
 * 右下角有两个短斜线,类似便签
 *
 * @author lu
 * @date 2017/8/22 17:55
 */
public class MomoLayout extends RelativeLayout {
    private Paint paint;

    public MomoLayout(@NonNull Context context) {
        this(context, null);
    }

    public MomoLayout(@NonNull Context context, @Nullable AttributeSet attrs) {
        this(context, attrs, 0);
    }


    public MomoLayout(@NonNull Context context, @Nullable AttributeSet attrs, @AttrRes int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

    @RequiresApi(api = VERSION_CODES.LOLLIPOP)
    public MomoLayout(@NonNull Context context, @Nullable AttributeSet attrs, @AttrRes int defStyleAttr, @StyleRes int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
        init();
    }

    private void init() {

        setWillNotDraw(false);//开启onDraw()方法。背景为空时，onDraw(),被优化掉，将不调用

        paint = new Paint(Paint.ANTI_ALIAS_FLAG);
        paint.setColor(Color.BLUE);
        paint.setStrokeWidth(2);

        TypedValue typedValue = new TypedValue();
        Theme theme = getContext().getTheme();
        boolean found = theme.resolveAttribute(android.R.attr.colorPrimary, typedValue, true);
        if (!found) {
            found = theme.resolveAttribute(android.R.attr.colorPrimaryDark, typedValue, true);
            if (!found) {
                theme.resolveAttribute(android.R.attr.colorAccent, typedValue, true);
            }
        }

        int id = typedValue.resourceId;
        if (id > 0) {
            int color = getResources().getColor(id);
            paint.setColor(color);
        } else {
            paint.setColor(0x55000000);
        }
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        drawSlash(canvas);
        drawMarginLine(canvas);
    }


    /**
     * 绘制外边框
     *
     * @param canvas
     */
    private void drawMarginLine(Canvas canvas) {
        paint.setStyle(Style.STROKE);
        float strokeWidth = paint.getStrokeWidth();
        float offset = strokeWidth / 2f;
        if (getWidth() > offset && getHeight() > offset) {
            canvas.drawRect(0 + offset, 0 + offset, getWidth() - offset, getHeight() - offset, paint);
        }

    }

    /**
     * 绘制斜线
     *
     * @param canvas
     */
    private void drawSlash(Canvas canvas) {

        paint.setStyle(Style.FILL);
        float limitW = getWidth() - 10f;
        float limitH = getHeight() - 10f;
        if (limitH > 0 && limitW > 0) {
            float startX1 = limitW - limitW / 25f;
            float startY1 = limitH;
            float stopX1 = limitW;
            float stopY1 = limitH - limitH / 25f;

            canvas.drawLine(startX1, startY1, stopX1, stopY1, paint);

            float startX2 = limitW - limitW / 50f;
            float startY2 = limitH;
            float stopX2 = limitW;
            float stopY2 = limitH - limitH / 50f;

            canvas.drawLine(startX2, startY2, stopX2, stopY2, paint);
        }
    }
}

其他说明：

• 一般用于包裹View;
• 为方便布局，继承自RelativeLayout
• 没有自定义属性
• 使用方式和普通的 RelativeLayout 一样
• 描边方式为内描边，线宽2px

——end