[移动开发]Android 图片显示依附位置（上下左右及中心位置）

1.说明：在 ImageView 的ScaleType.FIT_CENTER?基础上拓展

package com.example.view;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.Rect;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.util.Log;

import androidx.annotation.Nullable;
import androidx.appcompat.widget.AppCompatImageView;

public class FitScaleImageView extends AppCompatImageView {
    private String TAG = getClass().getName();
    private FitScaleType mFitScaleType = FitScaleType.FIT_CENTER;//默认 中心位置

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

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

    public FitScaleImageView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        setScaleType(ScaleType.FIT_CENTER);//设置固定缩放模式
        Drawable drawable = getDrawable();
        Matrix imageMatrix = getImageMatrix();
        if (drawable != null && imageMatrix != null) {
            float[] mv = new float[9];
            imageMatrix.getValues(mv);
            Rect bounds = drawable.getBounds();
            if (getWidth() > bounds.width() && getHeight() > bounds.height()) {
                mv[Matrix.MSCALE_X] = 1;
                mv[Matrix.MSCALE_Y] = 1;
            }
            float scaleWidth = bounds.width() * mv[Matrix.MSCALE_X];
            float scaleHeight = bounds.height() * mv[Matrix.MSCALE_Y];
            switch (mFitScaleType) {
                case FIT_CENTER_HORIZONTAL_TOP:
                    mv[Matrix.MTRANS_X] = (getWidth() - scaleWidth) / 2;
                    mv[Matrix.MTRANS_Y] = 0;
                    imageMatrix.setValues(mv);
                    break;
                case FIT_CENTER_HORIZONTAL_BOTTOM:
                    mv[Matrix.MTRANS_X] = (getWidth() - scaleWidth) / 2;
                    mv[Matrix.MTRANS_Y] = getHeight() - scaleHeight;
                    imageMatrix.setValues(mv);
                    break;
                case FIT_CENTER_VERTICAL_LEFT:
                    mv[Matrix.MTRANS_X] = 0;
                    mv[Matrix.MTRANS_Y] = (getHeight() - scaleHeight) / 2;
                    imageMatrix.setValues(mv);
                    break;
                case FIT_CENTER_VERTICAL_RIGHT:
                    mv[Matrix.MTRANS_X] = getWidth() - scaleWidth;
                    mv[Matrix.MTRANS_Y] = (getHeight() - scaleHeight) / 2;
                    imageMatrix.setValues(mv);
                    break;
                case FIT_LEFT_TOP:
                    mv[Matrix.MTRANS_X] = 0;
                    mv[Matrix.MTRANS_Y] = 0;
                    imageMatrix.setValues(mv);
                    break;
                case FIT_LEFT_BOTTOM:
                    mv[Matrix.MTRANS_X] = 0;
                    mv[Matrix.MTRANS_Y] = getHeight() - scaleHeight;
                    imageMatrix.setValues(mv);
                    break;
                case FIT_RIGHT_TOP:
                    mv[Matrix.MTRANS_X] = getWidth() - scaleWidth;
                    mv[Matrix.MTRANS_Y] = 0;
                    imageMatrix.setValues(mv);
                    break;
                case FIT_RIGHT_BOTTOM:
                    mv[Matrix.MTRANS_X] = getWidth() - scaleWidth;
                    mv[Matrix.MTRANS_Y] = getHeight() - scaleHeight;
                    imageMatrix.setValues(mv);
                    break;
                case FIT_CENTER:
                    mv[Matrix.MTRANS_X] = (getWidth() - scaleWidth) / 2;
                    mv[Matrix.MTRANS_Y] = (getHeight() - scaleHeight) / 2;
                    imageMatrix.setValues(mv);
                    break;
            }
            super.onDraw(canvas);
            Log.e(TAG, "MSCALE_X=" + mv[Matrix.MSCALE_X] + ",MSCALE_Y=" + mv[Matrix.MSCALE_Y] + ",MTRANS_X=" + mv[Matrix.MTRANS_X] + ",MTRANS_Y=" + mv[Matrix.MTRANS_Y] + "," + ",bd=" + bounds.toString() + ",cw=" + getWidth() + ",ch=" + getHeight() + ",scaleWidth=" + scaleWidth + ",scaleHeight=" + scaleHeight);
        } else {
            super.onDraw(canvas);
        }

    }

    /**
     * 设置 图片依附位置
     * @param fitScaleType 依附类型
     */
    public void setFitScaleType(FitScaleType fitScaleType) {
        mFitScaleType = fitScaleType;
    }

    public enum FitScaleType {
        /**
         * 依附 左上角
         */
        FIT_LEFT_TOP(0),
        /**
         * 依附 左下角
         */
        FIT_LEFT_BOTTOM(1),
        /**
         * 依附 右上角
         */
        FIT_RIGHT_TOP(2),
        /**
         * 依附 右下角
         */
        FIT_RIGHT_BOTTOM(3),
        /**
         * 依附 顶部且横向居中
         */
        FIT_CENTER_HORIZONTAL_TOP(4),
        /**
         * 依附 底部且横向居中
         */
        FIT_CENTER_HORIZONTAL_BOTTOM(5),
        /**
         * 依附 左边且垂直居中
         */
        FIT_CENTER_VERTICAL_LEFT(6),
        /**
         * 依附 右边且垂直居中
         */
        FIT_CENTER_VERTICAL_RIGHT(7),
        /**
         * 依附 中心位置
         */
        FIT_CENTER(8);

        FitScaleType(int ni) {
            nativeInt = ni;
        }

        final int nativeInt;
    }

}