在自定义ImageView中缩放图像

Question

I'm extending ImageView in order to manually scale an image within the view. I want to scale an image to fill the width of the custom view, and then draw it to the canvas, however, I'm unable to get the view width using this.getWidth() It just returns 0, as the view has not yet been drawn and so has dimensions 0 by 0.

Currently I have the following in my main.xml:

<com.android.myapp.BackgroundView
    android:id="@+id/background_view"
    android:layout_height="fill_parent"
    android:layout_width="fill_parent"
    android:src="@drawable/background"
    android:dither="true"
    />

The custom class is as follows:

public class BackgroundView extends ImageView {

    private Paint paint;
    private Bitmap background;

    public BackgroundView(Context context) {
        super(context);
        paint = new Paint();
        loadBitmap();
    }

    public BackgroundView(Context context, AttributeSet attrs) {
        super(context, attrs);
        paint = new Paint();
        loadBitmap();
    }

    public void loadBitmap() {
        BitmapDrawable src = (BitmapDrawable) this.getDrawable();
        background = src.getBitmap();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawBitmap(background, 0, 0, paint);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    }

}

My Main.java class is:

public class Main extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    }

I can't use
Bitmap.createScaledBitmap(background, view.getWidth(), view.getHeight(), false)
as the view hasn't yet been drawn, how would I go about scaling the image to fill the view/screen width at this point?

Thanks in advance.

Answer 1

I believe what you want to do could also be achieved by using ImageView directly in conjunction with the scaleType attribute. Either use fitXY or centerCrop , depending on your needs.

But to answer the question, you can only use getWidth() and getHeight() after layout() has been called. So you should be able to use the values inside your onDraw method.

Also you could use another drawBitmap method so you wouldn't have to create a new bitmap in memory.