Android：如何居中裁剪视图的背景？

Question

我不想在视图中插入图像视图，我只想将位图设置为视图的背景。但我想要位图 centerCropped。默认情况下，位图背景会被拉伸以适应视图的边界。

Answer 1

您可以通过实现自定义背景可绘制对象来做到这一点。

我实现了一个BitmapDrawable 的子类，它可以居中裁剪位图（基本上覆盖了onDraw(Canvas) 方法）。

代码：

package com.github.premnirmal;

import android.content.res.Resources;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.drawable.BitmapDrawable;

/**
 * A subclass of bitmap drawable that scales the bitmap to CenterCrop
 * Copyright Prem Nirmal 2016 MIT License
 * @author PremNirmal
 */
public class CenterCropBitmapDrawable extends BitmapDrawable {

  private final int viewWidth, viewHeight;

  public CenterCropBitmapDrawable(Resources res, Bitmap bitmap, int viewWidth, int viewHeight) {
    super(res, bitmap);
    this.viewWidth = viewWidth;
    this.viewHeight = viewHeight;
  }

  @Override public void draw(Canvas canvas) {
    final Matrix drawMatrix = new Matrix();
    final int dwidth = getIntrinsicWidth();
    final int dheight = getIntrinsicHeight();

    final int vwidth = viewWidth;
    final int vheight = viewHeight;

    float scale;
    float dx = 0, dy = 0;
    int saveCount = canvas.getSaveCount();
    canvas.save();
    if (dwidth * vheight > vwidth * dheight) {
      scale = (float) vheight / (float) dheight;
      dx = (vwidth - dwidth * scale) * 0.5f;
    } else {
      scale = (float) vwidth / (float) dwidth;
      dy = (vheight - dheight * scale) * 0.5f;
    }

    drawMatrix.setScale(scale, scale);
    drawMatrix.postTranslate(Math.round(dx), Math.round(dy));
    canvas.concat(drawMatrix);

    canvas.drawBitmap(getBitmap(), 0, 0, getPaint());

    canvas.restoreToCount(saveCount);
  }
}