以下代码用于缩放图像作为纵横比:

Bitmap bitmapImage = BitmapFactory.decodeFile("Your path");
int nh = (int) ( bitmapImage.getHeight() * (512.0 / bitmapImage.getWidth()) );
Bitmap scaled = Bitmap.createScaledBitmap(bitmapImage, 512, nh, true);
your_imageview.setImageBitmap(scaled);

这是它在ConstraintLayout中为我工作的方式:

<ImageView
    android:id="@+id/myImg"
    android:layout_width="300dp"
    android:layout_height="300dp"
    android:scaleType="fitCenter"
    android:adjustViewBounds="true"/>

然后在代码中，我设置drawable为:

ImageView imgView = findViewById(R.id.myImg);
imgView.setImageDrawable(ResourcesCompat.getDrawable(getResources(), R.drawable.image_to_show, null));

这很好地符合图像的长宽比，并保持它在中心。

Yes, by default Android will scale your image down to fit the ImageView, maintaining the aspect ratio. However, make sure you're setting the image to the ImageView using android:src="..." rather than android:background="...". src= makes it scale the image maintaining aspect ratio, but background= makes it scale and distort the image to make it fit exactly to the size of the ImageView. (You can use a background and a source at the same time though, which can be useful for things like displaying a frame around the main image, using just one ImageView.) You should also see android:adjustViewBounds to make the ImageView resize itself to fit the rescaled image. For example, if you have a rectangular image in what would normally be a square ImageView, adjustViewBounds=true will make it resize the ImageView to be rectangular as well. This then affects how other Views are laid out around the ImageView. Then as Samuh wrote, you can change the way it default scales images using the android:scaleType parameter. By the way, the easiest way to discover how this works would simply have been to experiment a bit yourself! Just remember to look at the layouts in the emulator itself (or an actual phone) as the preview in Eclipse is usually wrong.

传递你的ImageView，根据屏幕的高度和宽度，你可以做出它

    public void setScaleImage(EventAssetValueListenerView view){
        // Get the ImageView and its bitmap
        Drawable drawing = view.getDrawable();
        Bitmap bitmap = ((BitmapDrawable)drawing).getBitmap();
        // Get current dimensions
        int width = bitmap.getWidth();
        int height = bitmap.getHeight();

        float xScale = ((float) 4) / width;
        float yScale = ((float) 4) / height;
        float scale = (xScale <= yScale) ? xScale : yScale;

        Matrix matrix = new Matrix();
        matrix.postScale(scale, scale);

        Bitmap scaledBitmap = Bitmap.createBitmap(bitmap, 0, 0, width, height, matrix, true);
        BitmapDrawable result = new BitmapDrawable(scaledBitmap);
        width = scaledBitmap.getWidth();
        height = scaledBitmap.getHeight();

        view.setImageDrawable(result);

        LinearLayout.LayoutParams params = (LinearLayout.LayoutParams) view.getLayoutParams();
        params.width = width;
        params.height = height;
        view.setLayoutParams(params);
    }

看一下ImageView。ScaleType来控制和理解在ImageView中发生大小调整的方式。当图像被调整大小时(同时保持其纵横比)，图像的高度或宽度可能会小于ImageView的维度。

你不需要任何java代码。你只需要:

<ImageView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:adjustViewBounds="true"
android:scaleType="centerCrop" />

键在width和height的匹配父项中