thread causing application to crash

EDIT:

just incase you read this i got the problem sorted i had gotten confused by my layouts and was editing the wrong one when i realised this all was sorted!

END EDIT!

every time i add a thread to my application it causes it to crash when the activity containing the thread is called below is the code piece containing the thread:

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.cam);

    Toast t = Toast.makeText(this, "Just Click The Magnifying Glass To Search", 5000); //creates a new pop up message that lasts for 5 seconds

    t.setGravity(Gravity.CENTER|Gravity.CENTER, 0, 0);
    t.show()开发者_如何学JAVA;

    bt = (ImageButton)findViewById(R.id.button); //creates instance of button
    bt.setOnClickListener(search); //starts an on click listener for button

    preview = (SurfaceView)findViewById(R.id.myview); //creates instance of surfaceview
    previewHolder = preview.getHolder(); //creates a surfaceholder
    previewHolder.addCallback(this); //sets surfaceholder callback as the activity
    previewHolder.setType(3); //sets the type to SURFACE_TYPE_PUSH_BUFFERS 

    th = new Thread() {
        public void run() {
            handler.post(new Runnable() {
                public void run() {
                    tv.setVisibility(0);
                }
            });
        }
    };
    th.start();
}

if anyone could shed some light on the situation it would be greatly appreciated

EDIT:

i have got the thread working and got it to call a method which creates Toast however when i try to modify a setting of the textview it throws an NullPointerException error

I don't see initialization of TextView tv in your code (tv = (TextView)findViewById(R.id.id_of_textview);). May be it is the cause of the problem?

To show TextView after 5 seconds, you can use handler.postDelayed()

If you're doing TextView tv = new TextView(); then this is wrong and even if you're doing TextView tv = (TextView)findViewById(R.id.tv); then the layout will not be inflated before setContentView(); so you have to initialize tv in onCreate() method.