java - Android - 自定义 ImageView，带有勾选标记图像为选定状态

Question

对于我正在构建的 Android 应用程序，我制作了一个自定义 ImageView 类，它需要在图像上显示一个勾号，表明该图像已被选择。我从可绘制资源加载了刻度图像并将其显示在图像顶部，效果很好。但我想做的是，当刻度线可见时(即选择图像时)，图像变暗，以便您可以清楚地看到刻度线。我怎样才能做到这一点？

目前我的代码如下:

public class TickedImageView extends ImageView {

private boolean selected = true;
private Bitmap tickBmp;
private Paint paint = new Paint();

public TickedImageView(Context context) {
    super(context);
    tickBmp = BitmapFactory.decodeResource(getResources(), R.drawable.ic_done_white_48dp);
}

public TickedImageView(Context context, AttributeSet attrs) {
    super(context, attrs);
    tickBmp = BitmapFactory.decodeResource(getResources(), R.drawable.ic_done_white_48dp);
}

public void setSelected(boolean selected) {
    this.selected = selected;
    invalidate();
}

public boolean isSelected() {
    return selected;
}

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

    if(selected) {
        int margin = 15;
        int x = (canvas.getWidth() / 2) - (tickBmp.getWidth() / 2) - margin;
        int y = (canvas.getHeight() / 2) - (tickBmp.getHeight() / 2) - margin;

        canvas.drawBitmap(tickBmp, x, y, paint);
    }
}
}

谢谢。

Answer 1

在 Canvas 中，在原始图像的顶部绘制另一个带有深色和一点透明度的矩形。见下文

public class TickedImageView extends ImageView {

    private boolean selected = true;
    private Bitmap tickBmp;
    private Paint paint;
    private Paint mDarkerPaint;
    private int measuredWidth, measuredHeight;

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

    public TickedImageView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    private void init() {
        paint = new Paint();
        mDarkerPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mDarkerPaint.setStyle(Paint.Style.FILL);
        // Keep changing this color till it looks ok for you
        mDarkerPaint.setColor(0x80142030);
        tickBmp = BitmapFactory.decodeResource(getResources(), R.drawable.ic_done_white_48dp);
    }


    public void setSelected(boolean selected) {
        this.selected = selected;
        invalidate();
    }

    public boolean isSelected() {
        return selected;
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        measuredHeight = getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec);
        measuredWidth = getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec);

        setMeasuredDimension(measuredWidth, measuredHeight);
    }

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

        if (selected) {
            int margin = 15;
            int x = (canvas.getWidth() / 2) - (tickBmp.getWidth() / 2) - margin;
            int y = (canvas.getHeight() / 2) - (tickBmp.getHeight() / 2) - margin;

            canvas.drawRect(0, 0, measuredWidth, measuredHeight, mDarkerPaint);
            canvas.drawBitmap(tickBmp, x, y, paint);
        }
    }
}