已测量过的View生成Bitmap

即经过测量、布局、绘制并显示在界面上的View，此类View无需再次进行测量和布局，可直接将内容绘制到指定的Bitmap上。

/**
 * 绘制已经测量过的View
 */
private static Bitmap drawMeasureView(View view) {
    int width = view.getWidth();
    int height = view.getHeight();
    Bitmap bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.RGB_565);
    Canvas canvas = new Canvas(bitmap);
    view.draw(canvas);
    return bitmap;
}

未测量过的View生成Bitmap

直接Inflate后并未显示在界面的View，此类View必须手动进行测量和布局后，方可进行绘制，否则获取不到对应的宽高和内容。

/**
 * 先测量和布局，再生成Bitmap
 */
public static Bitmap getBitmap(View view) {
    // 测量
    int widthSpec = View.MeasureSpec.makeMeasureSpec(screenWidth, View.MeasureSpec.AT_MOST);
    int heightSpec = View.MeasureSpec.makeMeasureSpec(screenHeight, View.MeasureSpec.AT_MOST);
    view.measure(widthSpec, heightSpec);
    // 布局
    int measuredWidth = view.getMeasuredWidth();
    int measuredHeight = view.getMeasuredHeight();
    view.layout(0, 0, measuredWidth, measuredHeight);
    // 绘制
    int width = view.getWidth();
    int height = view.getHeight();
    Bitmap bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.RGB_565);
    Canvas canvas = new Canvas(bitmap);
    view.draw(canvas);
    return bitmap;
}

多张Bitmap合并为一张

将多张Bitmap按顺序从上到下合并为一张，如果图片的宽度不同，则进行等比缩放后再进行合并绘制。

/**
 * 将用户输入的图片从上到下拼接到一起
 * 如果图片宽度不一致，则进行等比缩放后再拼接
 */
public static Bitmap concat(Bitmap... bitmaps) {
    // 获取图片的最大宽度
    int maxWidth = bitmaps[0].getWidth();
    for (Bitmap bitmap : bitmaps) {
        maxWidth = Math.max(maxWidth, bitmap.getWidth());
    }
    // 对图片进行缩放并计算拼接后的图片高度
    int totalHeight = 0;
    for (int i = 0; i < bitmaps.length; i++) {
        Bitmap bitmap = bitmaps[i];
        int width = bitmap.getWidth();
        int height = bitmap.getHeight();
        float scale = maxWidth * 1f / width;
        int scaleHeight = (int) (height * scale);
        totalHeight = totalHeight + scaleHeight;
        bitmaps[i] = Bitmap.createScaledBitmap(bitmap, maxWidth, scaleHeight, false);
    }
    // 从上到下依次拼接
    Bitmap newBitmap = Bitmap.createBitmap(maxWidth, totalHeight, Bitmap.Config.RGB_565);
    Canvas canvas = new Canvas(newBitmap);
    int offsetTop = 0;
    for (Bitmap bitmap : bitmaps) {
        int height = bitmap.getHeight();
        canvas.drawBitmap(bitmap, 0, offsetTop, null);
        offsetTop += height;
    }
    return newBitmap;
}