Android图像缩放问题

Question

I'm new to Android and coming from IOS and encountered a small issue. I have an image that is quite long, so that on a tablet the image spans the whole screen without scaling the image.

But when i open the app on the phone the image is compressed in height to fit the screen. How do i stop this?

The image is set as a background on a LinearLayout:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:orientation="vertical" android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@drawable/blur"/>

i tried:

android:scaleType="fitStart"
android:scaleType="center"
android:scaleType="fitcenter

"

Answer 1

Android always scales backgrounds to fit its View, the scaleType only applies to ImageViews. You need to implement an ImageView with android:src reference to your image. Only then can you start playing with android:scaleType .

Answer 2

If you are trying to fit or scale your image into image view you can try this code.

public class ScalingUtilities {
   /**
 * Utility function for decoding an image resource. The decoded bitmap will
 * be optimized for further scaling to the requested destination dimensions
 * and scaling logic.
 * @param res The resources object containing the image data
 * @param resId The resource id of the image data
 * @param dstWidth Width of destination area
 * @param dstHeight Height of destination area
 * @param scalingLogic Logic to use to avoid image stretching
 * @return Decoded bitmap
 */
public static Bitmap decodeResource(Resources res, int resId, int dstWidth, int dstHeight,
        ScalingLogic scalingLogic) {
    Options options = new Options();
    options.inJustDecodeBounds = true;
    BitmapFactory.decodeResource(res, resId, options);
    options.inJustDecodeBounds = false;
    options.inSampleSize = calculateSampleSize(options.outWidth, options.outHeight, dstWidth,
            dstHeight, scalingLogic);
    Bitmap unscaledBitmap = BitmapFactory.decodeResource(res, resId, options);

    return unscaledBitmap;
}

/**
 * Utility function for creating a scaled version of an existing bitmap
 *
 * @param unscaledBitmap Bitmap to scale
 * @param dstWidth Wanted width of destination bitmap
 * @param dstHeight Wanted height of destination bitmap
 * @param scalingLogic Logic to use to avoid image stretching
 * @return New scaled bitmap object
 */
public static Bitmap createScaledBitmap(Bitmap unscaledBitmap, int dstWidth, int dstHeight,
        ScalingLogic scalingLogic) {
    Rect srcRect = calculateSrcRect(unscaledBitmap.getWidth(), unscaledBitmap.getHeight(),
            dstWidth, dstHeight, scalingLogic);
    Rect dstRect = calculateDstRect(unscaledBitmap.getWidth(), unscaledBitmap.getHeight(),
            dstWidth, dstHeight, scalingLogic);
    Bitmap scaledBitmap = Bitmap.createBitmap(dstRect.width(), dstRect.height(),
            Config.ARGB_8888);
    Canvas canvas = new Canvas(scaledBitmap);
    canvas.drawBitmap(unscaledBitmap, srcRect, dstRect, new Paint(Paint.FILTER_BITMAP_FLAG));

    return scaledBitmap;
}

/**
 * ScalingLogic defines how scaling should be carried out if source and
 * destination image has different aspect ratio.
 *
 * CROP: Scales the image the minimum amount while making sure that at least
 * one of the two dimensions fit inside the requested destination area.
 * Parts of the source image will be cropped to realize this.
 *
 * FIT: Scales the image the minimum amount while making sure both
 * dimensions fit inside the requested destination area. The resulting
 * destination dimensions might be adjusted to a smaller size than
 * requested.
 */
public static enum ScalingLogic {
    CROP, FIT
}

/**
 * Calculate optimal down-sampling factor given the dimensions of a source
 * image, the dimensions of a destination area and a scaling logic.
 *
 * @param srcWidth Width of source image
 * @param srcHeight Height of source image
 * @param dstWidth Width of destination area
 * @param dstHeight Height of destination area
 * @param scalingLogic Logic to use to avoid image stretching
 * @return Optimal down scaling sample size for decoding
 */
public static int calculateSampleSize(int srcWidth, int srcHeight, int dstWidth, int dstHeight,
        ScalingLogic scalingLogic) {
    if (scalingLogic == ScalingLogic.FIT) {
        final float srcAspect = (float)srcWidth / (float)srcHeight;
        final float dstAspect = (float)dstWidth / (float)dstHeight;

        if (srcAspect > dstAspect) {
            return srcWidth / dstWidth;
        } else {
            return srcHeight / dstHeight;
        }
    } else {
        final float srcAspect = (float)srcWidth / (float)srcHeight;
        final float dstAspect = (float)dstWidth / (float)dstHeight;

        if (srcAspect > dstAspect) {
            return srcHeight / dstHeight;
        } else {
            return srcWidth / dstWidth;
        }
    }
}

/**
 * Calculates source rectangle for scaling bitmap
 *
 * @param srcWidth Width of source image
 * @param srcHeight Height of source image
 * @param dstWidth Width of destination area
 * @param dstHeight Height of destination area
 * @param scalingLogic Logic to use to avoid image stretching
 * @return Optimal source rectangle
 */
public static Rect calculateSrcRect(int srcWidth, int srcHeight, int dstWidth, int dstHeight,
        ScalingLogic scalingLogic) {
    if (scalingLogic == ScalingLogic.CROP) {
        final float srcAspect = (float)srcWidth / (float)srcHeight;
        final float dstAspect = (float)dstWidth / (float)dstHeight;

        if (srcAspect > dstAspect) {
            final int srcRectWidth = (int)(srcHeight * dstAspect);
            final int srcRectLeft = (srcWidth - srcRectWidth) / 2;
            return new Rect(srcRectLeft, 0, srcRectLeft + srcRectWidth, srcHeight);
        } else {
            final int srcRectHeight = (int)(srcWidth / dstAspect);
            final int scrRectTop = (int)(srcHeight - srcRectHeight) / 2;
            return new Rect(0, scrRectTop, srcWidth, scrRectTop + srcRectHeight);
        }
    } else {
        return new Rect(0, 0, srcWidth, srcHeight);
    }
}

/**
 * Calculates destination rectangle for scaling bitmap
 *
 * @param srcWidth Width of source image
 * @param srcHeight Height of source image
 * @param dstWidth Width of destination area
 * @param dstHeight Height of destination area
 * @param scalingLogic Logic to use to avoid image stretching
 * @return Optimal destination rectangle
 */
public static Rect calculateDstRect(int srcWidth, int srcHeight, int dstWidth, int dstHeight,
        ScalingLogic scalingLogic) {
    if (scalingLogic == ScalingLogic.FIT) {
        final float srcAspect = (float)srcWidth / (float)srcHeight;
        final float dstAspect = (float)dstWidth / (float)dstHeight;

        if (srcAspect > dstAspect) {
            return new Rect(0, 0, dstWidth, (int)(dstWidth / srcAspect));
        } else {
            return new Rect(0, 0, (int)(dstHeight * srcAspect), dstHeight);
        }
    } else {
        return new Rect(0, 0, dstWidth, dstHeight);
    }
}}

Answer 3

Try changing the XML file to

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:background="@drawable/blur"/>

If your work is done then its okay else as per @ernir you have to use imageview .

Answer 4

LinearLayout has no android:scaleType attribute defined. You should use a ImageView and set your resource as android:src . Fit its size / positioning expanding to LinearLayout . And then you can use android:scaleType="centerCrop" attribute of ImageView

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">       

    <ImageView
        android:id="@+id/img" 
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:src="@drawable/blur"
        android:scaleType="centerCrop"
    />
</LinearLayout>