如何在Android中使自定义视图透明

Question

I am beginner in Android and I have a rather simple question. I have created a custom view and then injected it into another layout through xml. I want to make the background of this custom view transparent.

xml injection of my custom view:

<com.sagar.utils.ConnectDotsView
                android:id="@+id/connect_dots_view"
                android:layout_width="match_parent"
                android:layout_height="match_parent" />

Here is the code of the custom View:

public class ConnectDotsView extends View {

    private Bitmap mBitmap;
    private Canvas mCanvas;
    private Path mPath;
    private Paint mPaint;
    private static final int TOUCH_TOLERANCE_DP = 24;
    private static final int BACKGROUND = 0xFFDDDDDD;
    // Points to be connected.
    private List<Point> mPoints = new ArrayList<>();
    private int mLastPointIndex = 0;
    private int mTouchTolerance;
    private boolean isPathStarted = false;
    CompleteListener completeListener;

    public ConnectDotsView(Context context) {
        super(context);
        mCanvas = new Canvas();
        mPath = new Path();
        initPaint();
    }



    public interface CompleteListener {
        void onCompleteListener();
    }

    public void setOnCompleteListener(CompleteListener listener) {
        completeListener = listener;
    }

    public ConnectDotsView(Context context, AttributeSet attrs) {
        super(context, attrs);
        mCanvas = new Canvas();
        mPath = new Path();
        initPaint();
    }

    public ConnectDotsView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        mCanvas = new Canvas();
        mPath = new Path();
        initPaint();
    }

    public void clear() {
        mBitmap = Bitmap.createBitmap(getWidth(), getHeight(), Bitmap.Config.ARGB_8888);
        mBitmap.eraseColor(BACKGROUND);
        mCanvas.setBitmap(mBitmap);
        invalidate();
    }

    @Override
    protected void onSizeChanged(int width, int height, int oldWidth, int oldHeight) {
        super.onSizeChanged(width, height, oldWidth, oldHeight);
        clear();

    }

    @Override
    protected void onDraw(Canvas canvas) {
        canvas.drawColor(BACKGROUND);
        canvas.drawBitmap(mBitmap, 0, 0, null);
        canvas.drawPath(mPath, mPaint);

        mPaint.setColor(Color.parseColor("#56CBF9"));
        // TODO remove if you don't want points to be visible.
        for (Point point : mPoints) {
            canvas.drawPoint(point.x, point.y, mPaint);
            mPaint.setColor(Color.BLACK);
        }
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        float x = event.getX();
        float y = event.getY();

        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                touch_start(x, y);
                invalidate();
                break;
            case MotionEvent.ACTION_MOVE:
                touch_move(x, y);
                invalidate();
                break;
            case MotionEvent.ACTION_UP:
                touch_up(x, y);
                invalidate();
                break;
        }
        return true;
    }

    private void touch_start(float x, float y) {

        if (checkPoint(x, y, mLastPointIndex)) {
            mPath.reset();
            // User starts from given point so path can be drawn.
            isPathStarted = true;
        } else {
            // User starts move from point which does not belong to mPoints list
            isPathStarted = false;
        }

    }

    private void touch_move(float x, float y) {
        if (isPathStarted) {
            mPath.reset();
            Point point = mPoints.get(mLastPointIndex);
            mPath.moveTo(point.x, point.y);
            if (checkPoint(x, y, mLastPointIndex + 1)) {
                point = mPoints.get(mLastPointIndex + 1);
                mPath.lineTo(point.x, point.y);
                mCanvas.drawPath(mPath, mPaint);
                mPath.reset();
                ++mLastPointIndex;
            } else {
                int positionIndex = mLastPointIndex + 1;
                if (positionIndex >= mPoints.size()) {
                    completeListener.onCompleteListener();
                } else {
                    mPath.lineTo(x, y);
                }
            }
        }
    }

    private void touch_up(float x, float y) {
        mPath.reset();
        if (checkPoint(x, y, mLastPointIndex + 1) && isPathStarted) {
            // Move finished at valid point so I draw whole line.
            // That's the start point of current line segment.
            Point point = mPoints.get(mLastPointIndex);
            mPath.moveTo(point.x, point.y);
            // And that's the end point.
            point = mPoints.get(mLastPointIndex + 1);
            mPath.lineTo(point.x, point.y);
            mCanvas.drawPath(mPath, mPaint);
            mPath.reset();
            // Increment point index.
            ++mLastPointIndex;
            isPathStarted = false;
        }

    }

    /**
     * Checks if user touch point with some tolerance
     */
    private boolean checkPoint(float x, float y, int pointIndex) {
        if (pointIndex >= mPoints.size()) {
            // All dots already connected.
            return false;
        }
        Point point = mPoints.get(pointIndex);
        if (x > (point.x - mTouchTolerance) && x < (point.x + mTouchTolerance)) {
            if (y > (point.y - mTouchTolerance) && y < (point.y + mTouchTolerance)) {
                return true;
            }
        }
        return false;
    }

    /**
     * Sets up paint attributes.
     */
    private void initPaint() {
        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setDither(true);
        mPaint.setColor(Color.BLACK);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeJoin(Paint.Join.ROUND);
        mPaint.setStrokeCap(Paint.Cap.ROUND);
        mPaint.setStrokeWidth(12);
        mTouchTolerance = dp2px(TOUCH_TOLERANCE_DP);
    }

    /**
     * Converts dpi units to px
     *
     * @param dp
     * @return
     */
    private int dp2px(int dp) {
        Resources r = getContext().getResources();
        float px = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dp, r.getDisplayMetrics());
        return (int) px;
    }

    public void setPaint(Paint paint) {
        this.mPaint = paint;
    }

    public Bitmap getBitmap() {
        return mBitmap;
    }

    public List<Point> getPoints() {
        return mPoints;
    }

    public void setPoints(List<Point> points) {
        mLastPointIndex = 0;
        this.mPoints = points;
    }
}

I want to make the above custom View's background as transparent. How can I achieve that either through xml or code?

Thanks in advance.

Answer 1

使用view.setAlpha（float opacity）更改父视图的alpha，其中0f是完全透明视图。

Answer 2

In your Class ConnectDotsView change:

private static final int BACKGROUND = 0xFFDDDDDD;

to

private static final int BACKGROUND = Color.TRANSPARENT;

or

private static final int BACKGROUND = Color.parseColor("#00000000");

#00AABBCC = ARGB ( 00 is Alpha, AA is red, BB is green and CC is blue), 00 alpha is 0% and FF is 100%. This mean #00AABBCC will be transparent, #80AABBCC will be at 50% transparent and #FFAABBCC not transparent

Answer 3

In your initPaint() method, call the following function:

    setBackgroundColor(R.color.colorTransparent);

And in the values/colors.xml folder, set your colorTransparent with RGBA as 00:

<color name="colorTransparent">#00000000</color>

Alternatively, when you call your custom view in xml, use: android:background="#00000000".

This should solve your problem.

Edited:

just use setBackgroundColor(Color.TRANSPARENT);

Or setBackgroundColor(0x00000000);

50% opacity: setBackgroundColor(0x80000000);

Answer 4

To control the extent of transparency, use @Robillo's code, but modify this:

<color name="colorTransparent">#xy000000</color>

replace xy with your desired opacity. 00 will be 0% opaque, FF is 100% opaque (ie white colour)