Android实现倾斜角标样式

下面是详细的Android实现倾斜角标样式的攻略。

一、倾斜角标样式实现原理

倾斜角标样式是通过自定义View来实现的，具体实现过程如下：

1. 画出指定大小的带圆角的矩形背景。

2. 根据角标大小，以矩形的右上角为起点，绘制三角形。

3. 由于三角形是等腰三角形，需要计算出三角形的底边长和斜边长。

4. 将绘制好的背景和三角形按指定的位置进行组合。

5. 最后将组合后的图形绘制到View上即可。

二、示例一：使用Canvas实现倾斜角标样式

以下是使用Canvas实现倾斜角标样式的代码示例：

public class SkewedBadgeView extends View {

    private Paint mPaint;
    private Path mPath;
    private int mBackgroundColor = Color.RED;
    private int mTextColor = Color.WHITE;
    private int mBadgeSize;
    private int mTextSize;
    private String mBadgeText;

    public SkewedBadgeView(Context context) {
        super(context);
        init();
    }

    public SkewedBadgeView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    private void init() {
        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPath = new Path();
        mBadgeSize = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 20, getResources().getDisplayMetrics());
        mTextSize = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, 12, getResources().getDisplayMetrics());
    }

    public void setBadgeText(String badgeText) {
        mBadgeText = badgeText;
        invalidate();
    }

    public void setBadgeBackgroundColor(int color) {
        mBackgroundColor = color;
        invalidate();
    }

    public void setBadgeTextColor(int color) {
        mTextColor = color;
        invalidate();
    }

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

        int width = getWidth();
        int height = getHeight();

        // 绘制背景
        mPaint.setColor(mBackgroundColor);
        mPaint.setStyle(Paint.Style.FILL);
        RectF backgroundRect = new RectF(0, 0, width, height);
        int cornerRadius = height / 2;
        canvas.drawRoundRect(backgroundRect, cornerRadius, cornerRadius, mPaint);

        // 绘制角标
        mPath.moveTo(width - mBadgeSize, 0);
        mPath.lineTo(width - cornerRadius, 0);
        mPath.arcTo(new RectF(width - cornerRadius * 2, 0, width, cornerRadius * 2), -90, 90);
        mPath.lineTo(width, mBadgeSize);
        mPath.close();

        mPaint.setColor(mBackgroundColor);
        canvas.drawPath(mPath, mPaint);

        // 绘制角标文字
        if (!TextUtils.isEmpty(mBadgeText)) {
            mPaint.setColor(mTextColor);
            mPaint.setTextSize(mTextSize);
            mPaint.setTextAlign(Paint.Align.CENTER);
            Paint.FontMetrics fontMetrics = mPaint.getFontMetrics();
            float baseline = (backgroundRect.bottom + backgroundRect.top - fontMetrics.bottom - fontMetrics.top) / 2;
            canvas.drawText(mBadgeText, backgroundRect.centerX(), baseline, mPaint);
        }
    }
}

在以上代码中，我们通过绘制背景和三角形来实现倾斜角标样式，并通过设置get/set方法来动态修改样式。

三、示例二：使用Drawable实现倾斜角标样式

以下是使用Drawable实现倾斜角标样式的代码示例：

public class SkewedDrawable extends Drawable {

    private Paint mPaint;
    private Path mPath;
    private int mBackgroundColor = Color.RED;
    private int mTextColor = Color.WHITE;
    private int mBadgeSize;
    private int mTextSize;
    private String mBadgeText;

    public SkewedDrawable() {
        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPath = new Path();
        mBadgeSize = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 20, getResources().getDisplayMetrics());
        mTextSize = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, 12, getResources().getDisplayMetrics());
    }

    public void setBadgeText(String badgeText) {
        mBadgeText = badgeText;
        invalidateSelf();
    }

    public void setBadgeBackgroundColor(int color) {
        mBackgroundColor = color;
        invalidateSelf();
    }

    public void setBadgeTextColor(int color) {
        mTextColor = color;
        invalidateSelf();
    }

    @Override
    public void draw(@NonNull Canvas canvas) {
        Rect bounds = getBounds();
        int width = bounds.width();
        int height = bounds.height();

        // 绘制背景
        mPaint.setColor(mBackgroundColor);
        mPaint.setStyle(Paint.Style.FILL);
        RectF backgroundRect = new RectF(0, 0, width, height);
        int cornerRadius = height / 2;
        canvas.drawRoundRect(backgroundRect, cornerRadius, cornerRadius, mPaint);

        // 绘制角标
        mPath.moveTo(width - mBadgeSize, 0);
        mPath.lineTo(width - cornerRadius, 0);
        mPath.arcTo(new RectF(width - cornerRadius * 2, 0, width, cornerRadius * 2), -90, 90);
        mPath.lineTo(width, mBadgeSize);
        mPath.close();

        mPaint.setColor(mBackgroundColor);
        canvas.drawPath(mPath, mPaint);

        // 绘制角标文字
        if (!TextUtils.isEmpty(mBadgeText)) {
            mPaint.setColor(mTextColor);
            mPaint.setTextSize(mTextSize);
            mPaint.setTextAlign(Paint.Align.CENTER);
            Paint.FontMetrics fontMetrics = mPaint.getFontMetrics();
            float baseline = (backgroundRect.bottom + backgroundRect.top - fontMetrics.bottom - fontMetrics.top) / 2;
            canvas.drawText(mBadgeText, backgroundRect.centerX(), baseline, mPaint);
        }
    }

    @Override
    public void setAlpha(int alpha) {

    }

    @Override
    public void setColorFilter(@Nullable ColorFilter colorFilter) {

    }

    @Override
    public int getOpacity() {
        return PixelFormat.TRANSLUCENT;
    }
}

在以上代码中，我们通过Drawable来实现倾斜角标样式，并通过设置get/set方法来动态修改样式。

四、总结

通过以上两个示例的演示，我们可以了解到如何通过Canvas和Drawable来实现倾斜角标样式。当然，这只是其中的一种实现方式，开发者可以根据实际需求来进行改进，比如：实现不同形状的背景、实现不同样式的字体等。