java - 关闭虚拟机

Question

我正在学习android，请帮助我。它在 logcat 中给我以下错误。

02-27 14:14:42.455: D/dalvikvm(1655): GC_FOR_ALLOC freed 46K, 5% free 2891K/3020K, paused 152ms, total 156ms
02-27 14:14:42.465: I/dalvikvm-heap(1655): Grow heap (frag case) to 3.668MB for 810016-byte allocation
02-27 14:14:42.545: D/dalvikvm(1655): GC_FOR_ALLOC freed 2K, 4% free 3680K/3812K, paused 76ms, total 77ms
02-27 14:14:43.425: I/Choreographer(1655): Skipped 35 frames!  The application may be doing too much work on its main thread.
02-27 14:14:43.645: D/gralloc_goldfish(1655): Emulator without GPU emulation detected.
02-27 14:14:48.395: I/Choreographer(1655): Skipped 58 frames!  The application may be doing too much work on its main thread.
02-27 14:14:49.725: I/Choreographer(1655): Skipped 58 frames!  The application may be doing too much work on its main thread.
02-27 14:14:52.355: I/Choreographer(1655): Skipped 61 frames!  The application may be doing too much work on its main thread.
02-27 14:14:55.195: D/AndroidRuntime(1655): Shutting down VM
02-27 14:14:55.195: W/dalvikvm(1655): threadid=1: thread exiting with uncaught exception (group=0xb3aaaba8)
02-27 14:14:55.275: E/AndroidRuntime(1655): FATAL EXCEPTION: main
02-27 14:14:55.275: E/AndroidRuntime(1655): Process: com.example.dreamhome, PID: 1655
02-27 14:14:55.275: E/AndroidRuntime(1655): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.dreamhome/com.example.dreamhome.LoginFormActivity}: java.lang.NullPointerException
02-27 14:14:55.275: E/AndroidRuntime(1655):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
02-27 14:14:55.275: E/AndroidRuntime(1655):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
02-27 14:14:55.275: E/AndroidRuntime(1655):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
02-27 14:14:55.275: E/AndroidRuntime(1655):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
02-27 14:14:55.275: E/AndroidRuntime(1655):     at android.os.Handler.dispatchMessage(Handler.java:102)
02-27 14:14:55.275: E/AndroidRuntime(1655):     at android.os.Looper.loop(Looper.java:136)
02-27 14:14:55.275: E/AndroidRuntime(1655):     at android.app.ActivityThread.main(ActivityThread.java:5017)
02-27 14:14:55.275: E/AndroidRuntime(1655):     at java.lang.reflect.Method.invokeNative(Native Method)
02-27 14:14:55.275: E/AndroidRuntime(1655):     at java.lang.reflect.Method.invoke(Method.java:515)
02-27 14:14:55.275: E/AndroidRuntime(1655):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
02-27 14:14:55.275: E/AndroidRuntime(1655):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
02-27 14:14:55.275: E/AndroidRuntime(1655):     at dalvik.system.NativeStart.main(Native Method)
02-27 14:14:55.275: E/AndroidRuntime(1655): Caused by: java.lang.NullPointerException
02-27 14:14:55.275: E/AndroidRuntime(1655):     at com.example.dreamhome.LoginFormActivity.onCreate(LoginFormActivity.java:45)
02-27 14:14:55.275: E/AndroidRuntime(1655):     at android.app.Activity.performCreate(Activity.java:5231)
02-27 14:14:55.275: E/AndroidRuntime(1655):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
02-27 14:14:55.275: E/AndroidRuntime(1655):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
02-27 14:14:55.275: E/AndroidRuntime(1655):     ... 11 more
02-27 14:15:03.295: I/Process(1655): Sending signal. PID: 1655 SIG: 9

HomeActivity.java

public class HomeActivity extends Activity 
{
Button search_property, log_in, exit;


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

    search_property=(Button)findViewById(R.id.homebutton1);
    log_in=(Button)findViewById(R.id.homebutton2);
    exit=(Button)findViewById(R.id.homebutton3);


    search_property.setOnClickListener(new View.OnClickListener()
    {
        public void onClick(View v)
        {

            Intent main1=new Intent(HomeActivity.this,EndUserSearchPropertyActivity.class);
            startActivity(main1);

        }
    });


    log_in.setOnClickListener(new View.OnClickListener()
    {
        public void onClick(View v)
        {

            Intent main2 = new Intent(HomeActivity.this,LoginFormActivity.class);
            startActivity(main2);

        }
    });


    exit.setOnClickListener(new View.OnClickListener()
    {
        public void onClick(View v)
        {
            finish();
            System.exit(0);

        }
    });



    // Show the Up button in the action bar.
    setupActionBar();
}

/**
 * Set up the {@link android.app.ActionBar}.
 */
private void setupActionBar() 
{

    getActionBar().setDisplayHomeAsUpEnabled(true);

}

@Override
public boolean onCreateOptionsMenu(Menu menu) 
{
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.home, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) 
{
    switch (item.getItemId()) 
    {
        case android.R.id.home:
        // This ID represents the Home or Up button. In the case of this
        // activity, the Up button is shown. Use NavUtils to allow users
        // to navigate up one level in the application structure. For
        // more details, see the Navigation pattern on Android Design:
        //
        // http://developer.android.com/design/patterns/navigation.html#up-vs-back
        //
        NavUtils.navigateUpFromSameTask(this);
        return true;
    }
    return super.onOptionsItemSelected(item);
}

这是LoginFormActivity.java

public class LoginFormActivity extends Activity 
{

 private Button sign_up = null;
 private Button btnSignIn = null;
 LoginDataBaseAdapter loginDataBaseAdapter = null;


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


     // create a instance of SQLite Database
    loginDataBaseAdapter=new LoginDataBaseAdapter(this);
    loginDataBaseAdapter=loginDataBaseAdapter.open();


    final Dialog dialog = new Dialog(LoginFormActivity.this);

    // get the Refferences of views
    final  EditText editTextUserName=(EditText)dialog.findViewById(R.id.login_editText1);
    final  EditText editTextPassword=(EditText)dialog.findViewById(R.id.login_editText2);

    btnSignIn = (Button)dialog.findViewById(R.id.login_form_button1);
    // Set On ClickListener
    btnSignIn.setOnClickListener(new View.OnClickListener() 
    {
        public void onClick(View v) 
        {
            // get The User name and Password
            String userName = editTextUserName.getText().toString();
            String password = editTextPassword.getText().toString();

            // fetch the Password form database for respective user name
            String storedPassword=loginDataBaseAdapter.getSinlgeEntry(userName);

            // check if the Stored password matches with  Password entered by user
            if(password.equals(storedPassword))
            {
                Toast.makeText(LoginFormActivity.this, "Congrats: Login Successfull", Toast.LENGTH_LONG).show();
                dialog.dismiss();
            }

            else
            {
                Toast.makeText(LoginFormActivity.this, "User Name or Password does not match", Toast.LENGTH_LONG).show();
            }
       }
  });

  dialog.show();
  }


 @Override
 protected void onDestroy() 
 {
     super.onDestroy();
     // Close The Database
     loginDataBaseAdapter.close();



    sign_up = (Button)findViewById(R.id.login_form_button2);

    sign_up.setOnClickListener(new View.OnClickListener()
    {
        public void onClick(View v)
        {

            Intent main2=new Intent(LoginFormActivity.this,SignupFormActivity.class);
            startActivity(main2);

        }
    });



    // Show the Up button in the action bar.
    setupActionBar();
}

/**
 * Set up the {@link android.app.ActionBar}.
 */
private void setupActionBar() 
{

    getActionBar().setDisplayHomeAsUpEnabled(true);

}

@Override
public boolean onCreateOptionsMenu(Menu menu) 
{
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.login_form, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) 
{
    switch (item.getItemId()) 
    {
        case android.R.id.home:
        // This ID represents the Home or Up button. In the case of this
        // activity, the Up button is shown. Use NavUtils to allow users
        // to navigate up one level in the application structure. For
        // more details, see the Navigation pattern on Android Design:
        //
        // http://developer.android.com/design/patterns/navigation.html#up-vs-back
        //
        NavUtils.navigateUpFromSameTask(this);
        return true;
    }
    return super.onOptionsItemSelected(item);
}

Answer 1

final Dialog dialog = new Dialog(LoginFormActivity.this);

仅仅实例化一个对话框并不会膨胀/创建它的布局。所有后续的 dialog.findViewById() 调用都返回 null 并且您将在此处看到 NPE 试图在 null 引用上调用方法:

btnSignIn = (Button)dialog.findViewById(R.id.login_form_button1);
// Set On ClickListener
btnSignIn.setOnClickListener(new View.OnClickListener()

您可能需要为您的对话框设置一个内容 View ，其中包含您要引用的所有 View 。显示对话框后，可以通过 findViewById() 使用 View 。