Android在其他活动中编辑Drawable并将其设置为ImageView

Question

I have a method plotPoints(float x, float y) that I would like to use to plot a point on a drawable. I attempt to add a point to the drawable using a bitmap and canvas. Then, depending on whether plotPoints() has been called, I either set the the ImageView of a separate activity to the original drawable's bitmap (without the point), or the edited bitmap with the point. However, the ImageView always displays the original drawable, it never shows the drawn point. Please let me know if you can help.

Here is the related code:

Bitmap labBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.lab_image);

plotPoints() method:

    public void plotPoints(float x, float y) {
    pointsPlotted = true;

    //Paint for LocationActivity
    Paint labPaint = new Paint();
    labPaint.setColor(color.holo_purple);

    //Initialize tempBitmap and attach a new canvas to it    
    Bitmap tempBitmap = Bitmap.createBitmap(labBitmap.getWidth(), labBitmap.getHeight(), Bitmap.Config.ARGB_8888);
    Canvas tempCanvas = new Canvas(tempBitmap);

    //Draw the image Bitmap onto the Canvas
    tempCanvas.drawBitmap(labBitmap, 0, 0, null);

    //Set paint Color and draw X and Y coordinates on Canvas
    tempCanvas.drawPoint(x, y, labPaint);
}

Here is where I decide which bitmap to use and start the new activity:

    public void openLabView() {
    //Compress bitmap for smoother pass to LocationActivity
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    byte[] b;

    Intent intent = new Intent(this, LocationActivity.class);

    if(pointsPlotted) {
        tempBitmap.compress(Bitmap.CompressFormat.PNG, 100, baos);
        b = baos.toByteArray();
        intent.putExtra("imageBitmap", b);
    }
    else {
        labBitmap.compress(Bitmap.CompressFormat.PNG, 100, baos);
        b = baos.toByteArray();
        intent.putExtra("imageBitmap", b);
    }

    startActivity(intent);
}

And here is the onCreate() of the new activity:

    @Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_location);

    //Receive Bitmap for ImageView
    Bundle extras = getIntent().getExtras();
    byte[] b = extras.getByteArray("imageBitmap");

    Bitmap imageBitmap = BitmapFactory.decodeByteArray(b, 0, b.length);
    ImageView image = (ImageView) findViewById(R.id.lab_image);

    image.setImageBitmap(imageBitmap);
}

Answer 1

In your plotPoints() method, you define a Bitmap tempBitmap in that method's scope. So outside of that method ( openLabView() ) it has no reference to the tempBitmap from plotPoints() but maybe another same named Bitmap in the class scope. This might be a reason why the Bitmap generated in openLabView() doesn't seem to change.

May I suggest slightly renaming Bitmap tempBitmap in plotPoints() just for easier debugging, and see if that Bitmap inside plotPoints() can be passed to openLabView() , as that Bitmap should have been modified by the Canvas . (Basically the Bitmap passed to the Canvas constructor is what you want.)