动态将按钮添加到linearView

Question

I'm trying to write an application that's adding buttons dynamically. The application receives an image from the server and adding a button (no functionality for now).

The main activity is holding linear layout which will contain the buttons and a surface view that would receive the images and would create the buttons in the main activity.

The problem is that after the first image has been received the application crash while trying to add a new button to the view.

This is the surface view code:

public void run() {
        while ( isRunning){
            if ( !ourHolder.getSurface().isValid()){
                continue;
            }

            Canvas canvas = ourHolder.lockCanvas(); // Semafor for the canvas
            canvas.drawRGB(20,20,80);

            if (getNumOfBoards() > 0){
                canvas.drawBitmap(getCurrentBoard(), 0, 0, null);
            }

            ourHolder.unlockCanvasAndPost(canvas);
        }
    }

This is the Main Activity add button code

public void addButtons(int numOfButton) {
                // create patameter
                LinearLayout.LayoutParams p = new LinearLayout.LayoutParams(
                   LinearLayout.LayoutParams.WRAP_CONTENT,
                   LinearLayout.LayoutParams.WRAP_CONTENT
                );

                // create new button
                Button newbutton = new Button(this);

                // set background color
                newbutton.setBackgroundColor(Color.BLUE);

                // set width and height
                newbutton.setWidth(30);
                newbutton.setHeight(20);

                // set position
                newbutton.setY((float)numOfButton*20);
                newbutton.setX(0);

                // set text
                newbutton.setText("new button");

                // add button to the layout
                buttons.addView(newbutton,p);// **the application crash here**
    }

Answer 1

Due to the way android handles the Activities, the constructor onCreate is not guaranteed to have been called every time the addButtons method is executed (See the Activity Lifecycle Section at developer.android.com)

You had better find the buttons LinearLayout

LinearLayout buttons = (LinearLayout) findViewById(R.id.LayoutButtons);

in addButtons and add the new button.