Android - ImageView bottomCrop 而不是 centerCrop

Question

我正在尝试定位 ImageView，以使图像的底部始终固定在 View 的底部，无论 ImageView 的高度有多小。但是，似乎没有一种比例类型适合我想要做的事情。 CenterCrop 很接近，但我不希望图像居中。类似于 CSS 处理绝对定位的方式。

原因是，我需要为 ImageView 的高度设置动画，但让它看起来好像“显示”了图像的上部。我认为弄清楚这种裁剪图像和动画 ImageView 高度的方法是最简单的方法，但如果有人知道更好的方法，我希望被指出正确的方向。

任何帮助表示赞赏。

Answer 1

Jpoliachik's答案很酷，让我想将它概括为支持上/下和左/右，数量可变。 :) 现在顶部裁剪，只需调用 setCropOffset(0,0) ，底部裁剪 setCropOffset(0,1)，左侧裁剪也是 setCropOffset(0, 0)，然后右裁剪 setCropOffset(1,0)。如果您想在一维中将视口(viewport)偏移图像的一部分，您可以调用例如setCropOffset(0, 0.25f) 将其下移 25% 的不可见空间，而 0.5f 会将其居中。干杯!

/**
 * {@link android.widget.ImageView} that supports directional cropping in both vertical and
 * horizontal directions instead of being restricted to center-crop. Automatically sets {@link
 * android.widget.ImageView.ScaleType} to MATRIX and defaults to center-crop.
 */
public class CropImageView extends android.support.v7.widget.AppCompatImageView {
    private static final float DEFAULT_HORIZONTAL_OFFSET = 0.5f;
    private static final float DEFAULT_VERTICAL_OFFSET = 0.5f;

    private float mHorizontalOffsetPercent = DEFAULT_HORIZONTAL_OFFSET;
    private float mVerticalOffsetPercent = DEFAULT_VERTICAL_OFFSET;

    public CropImageView(Context context) {
        this(context, null);
    }

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

    public CropImageView(Context context, @Nullable AttributeSet attrs, @AttrRes int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        setScaleType(ScaleType.MATRIX);
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        applyCropOffset();
    }

    /**
     * Sets the crop box offset by the specified percentage values. For example, a center-crop would
     * be (0.5, 0.5), a top-left crop would be (0, 0), and a bottom-center crop would be (0.5, 1)
     */
    public void setCropOffset(float horizontalOffsetPercent, float verticalOffsetPercent) {
        if (mHorizontalOffsetPercent < 0
                || mVerticalOffsetPercent < 0
                || mHorizontalOffsetPercent > 1
                || mVerticalOffsetPercent > 1) {
            throw new IllegalArgumentException("Offset values must be a float between 0.0 and 1.0");
        }

        mHorizontalOffsetPercent = horizontalOffsetPercent;
        mVerticalOffsetPercent = verticalOffsetPercent;
        applyCropOffset();
    }

    private void applyCropOffset() {
        Matrix matrix = getImageMatrix();

        float scale;
        int viewWidth = getWidth() - getPaddingLeft() - getPaddingRight();
        int viewHeight = getHeight() - getPaddingTop() - getPaddingBottom();
        int drawableWidth = 0, drawableHeight = 0;
        // Allow for setting the drawable later in code by guarding ourselves here.
        if (getDrawable() != null) {
            drawableWidth = getDrawable().getIntrinsicWidth();
            drawableHeight = getDrawable().getIntrinsicHeight();
        }

        // Get the scale.
        if (drawableWidth * viewHeight > drawableHeight * viewWidth) {
            // Drawable is flatter than view. Scale it to fill the view height.
            // A Top/Bottom crop here should be identical in this case.
            scale = (float) viewHeight / (float) drawableHeight;
        } else {
            // Drawable is taller than view. Scale it to fill the view width.
            // Left/Right crop here should be identical in this case.
            scale = (float) viewWidth / (float) drawableWidth;
        }

        float viewToDrawableWidth = viewWidth / scale;
        float viewToDrawableHeight = viewHeight / scale;
        float xOffset = mHorizontalOffsetPercent * (drawableWidth - viewToDrawableWidth);
        float yOffset = mVerticalOffsetPercent * (drawableHeight - viewToDrawableHeight);

        // Define the rect from which to take the image portion.
        RectF drawableRect =
                new RectF(
                        xOffset,
                        yOffset,
                        xOffset + viewToDrawableWidth,
                        yOffset + viewToDrawableHeight);
        RectF viewRect = new RectF(0, 0, viewWidth, viewHeight);
        matrix.setRectToRect(drawableRect, viewRect, Matrix.ScaleToFit.FILL);

        setImageMatrix(matrix);
    }
}