如何在每次绘制到 UI 之前获取 ImageView 的高度和宽度（在 Fragment 中）

Question

我想将外部存储中的照片设置为（圆形）ImageView。 因此我有一个函数，它要求 ImageView 的高度和宽度来裁剪图片，然后将其设置为位图。

我的问题是，在加载 UI 之前调用此函数。 我遇到了解决方案，我第一次在 onViewCreated 中调用了这个函数，在那里我向 addOnWindowFocusChangeListener 添加了一个监听器。 这是第一次起作用。

该片段在 ViewPager 内，如果我转到左侧的片段，然后从中间转到右侧，它又消失了。

我对 StackOverflow 完全陌生。 我很欣赏每一个提示，我可以做得更好。

//This works for the First Time

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

        View m = getView();
        ViewTreeObserver n = m.getViewTreeObserver();
        n.addOnWindowFocusChangeListener(new ViewTreeObserver.OnWindowFocusChangeListener() {
            @Override
            public void onWindowFocusChanged(final boolean hasFocus) {
                // do your stuff here
                ImageUtil.setPic(binding.photoRoundProfile, mCurrentPhotoPath);

            }
        });
    }

//The function where I set the Picture into the ImageView

static public void setPic(ImageView mImageView, String pPath) {
        try {
            if (pPath == null) return;
            File f = new File(pPath);
            if (!f.exists() || f.isDirectory()) return;

            // Get the dimensions of the View
            int targetW = mImageView.getWidth();
            if (targetW == 0) targetW = mImageView.getMeasuredWidth();
            int targetH = mImageView.getHeight();
            if (targetH == 0) targetH = mImageView.getMeasuredHeight();

            // Get the dimensions of the bitmap
            BitmapFactory.Options bmOptions = new BitmapFactory.Options();
            bmOptions.inJustDecodeBounds = true;
            BitmapFactory.decodeFile(pPath, bmOptions);
            int photoW = bmOptions.outWidth;
            int photoH = bmOptions.outHeight;

            // Determine how much to scale down the image
            int scaleFactor = photoW / targetW; //Math.min(photoW/targetW, photoH/targetH);

            // Decode the image file into a Bitmap sized to fill the View
            bmOptions.inJustDecodeBounds = false;
            bmOptions.inSampleSize = scaleFactor;
            bmOptions.inPurgeable = true;

            Bitmap bitmap = BitmapFactory.decodeFile(pPath, bmOptions);
            Bitmap orientedBitmap = ExifUtil.rotateBitmap(pPath, bitmap);
            mImageView.setImageBitmap(orientedBitmap);

            //mImageView.setLayoutParams(new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, LinearLayout.LayoutParams.WRAP_CONTENT));
            mImageView.setAdjustViewBounds(true);
            mImageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

有个视频，为了更好的理解： https : //www.loom.com/share/05c4174562d74c9bba8ff02c9072c866

Answer 1

我找到了解决我的问题的方法。 我在OnPreDrawListener找到了onPreDraw方法。 每次更新ImageView都会运行此侦听器。 因此我添加了一个 if-Statement 来节省性能而不是每次都重绘。

@Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

        ImageView iv= binding.photoRoundProfile;
        ViewTreeObserver vto = iv.getViewTreeObserver();
        vto.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {

            private int mFinalWidth = 0;
            private int mFinalHeight = 0;

            public boolean onPreDraw() {

                if(mFinalHeight != 0 || mFinalWidth != 0)
                    return true;

                mFinalHeight = iv.getHeight();
                mFinalWidth = iv.getWidth();
                Log.d("hilength","Height: " + mFinalHeight + " Width: " + mFinalWidth);

                ImageUtil.setPic(binding.photoRoundProfile, mCurrentPhotoPath);
                return true;
            }
        });
    }