java NullPointerException Android处理程序

Question

    public class MainActivity extends ActionBarActivity {   
    Handler myHandler;
    Runnable myRunnable;
    TextView tv;
    int no;

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

        myHandler.post(myRunnable);
    }

    public void initialize(){
        no = 10;
        tv = (TextView) findViewById(R.id.textView1);

        myRunnable = new Runnable() {

            @Override
            public void run() {
                tv.setText(Integer.toString(no));
                no--;
                if(no != 0)
                myHandler.postDelayed(myRunnable, 1000);
            }
        };
    }
}

I tried forcing the Orientation to portrait to run this code but it failed again.

Whenever i try a handler to basically change the view text after every second i get this error.

Am new to Android development a college student so bear with my mistakes if any.

Thank you in advance.

The logs are below.

    10-04 04:22:35.750: E/AndroidRuntime(2123):FATAL EXCEPTION: main

    10-04 04:22:35.750: E/AndroidRuntime(2123):java.lang.RuntimeException: Unable to start activity ComponentInfo{we.funnycorps.handlerpractise/we.funnycorps.handlerpractise.MainActivity}: java.lang.NullPointerException

    10-04 04:22:35.750: E/AndroidRuntime(2123):at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)

    10-04 04:22:35.750: E/AndroidRuntime(2123):at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)

Answer 1

you have not used the initialize() function in oncreate ,below code use ,you will get the expected result.

public class Dummycls extends Activity {

Handler myHandler;
Runnable myRunnable;
TextView tv;
int no;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initialize();
//myHandler.post(myRunnable);
}

public void initialize(){
no = 10;
tv = (TextView) findViewById(R.id.pinchTitleText);

myHandler=new Handler();
myRunnable = new Runnable(){
    public void run() {
        tv.setText(Integer.toString(no));
        no--;
        if(no != 0)
        myHandler.postDelayed(myRunnable, 1000);

        //handler.postDelayed(r, 1000);


    }
}; 
myHandler.post(myRunnable);


   }
 }

Answer 2

initialize myHandler as

Handler myHandler = new Handler();

ie replace

Handler myHandler;

to

 Handler myHandler = new Handler();

And call initialize() method before myHandler.post(myRunnable); as

initialize();
myHandler.post(myRunnable);

Answer 3

myHandler未初始化，并且由于未在onCreate（）中调用initialize（）方法，因此在尝试发布myRunnable之前也未对其进行初始化。