android - 当我尝试显示对话框时，它给我强制关闭错误

Question

这是显示我的对话框 Activity 的代码。每当我尝试打开此 Intent 时，我的应用程序都会强制关闭。所以请告诉我代码中的错误。这是 logcat。

03-28 12:11:36.851: E/AndroidRuntime(681): FATAL EXCEPTION: main 03-28 12:11:36.851: E/AndroidRuntime(681): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.neelrazin.noteit/com.neelrazin.noteit.Password}: java.lang.NullPointerException 03-28 12:11:36.851: E/AndroidRuntime(681): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647) 03-28 12:11:36.851: E/AndroidRuntime(681): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663) 03-28 12:11:36.851: E/AndroidRuntime(681): at android.app.ActivityThread.access$1500(ActivityThread.java:117) 03-28 12:11:36.851: E/AndroidRuntime(681): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931) 03-28 12:11:36.851: E/AndroidRuntime(681): at android.os.Handler.dispatchMessage(Handler.java:99) 03-28 12:11:36.851: E/AndroidRuntime(681): at android.os.Looper.loop(Looper.java:123) 03-28 12:11:36.851: E/AndroidRuntime(681): at android.app.ActivityThread.main(ActivityThread.java:3683) 03-28 12:11:36.851: E/AndroidRuntime(681): at java.lang.reflect.Method.invokeNative(Native Method) 03-28 12:11:36.851: E/AndroidRuntime(681): at java.lang.reflect.Method.invoke(Method.java:507) 03-28 12:11:36.851: E/AndroidRuntime(681): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 03-28 12:11:36.851: E/AndroidRuntime(681): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 03-28 12:11:36.851: E/AndroidRuntime(681): at dalvik.system.NativeStart.main(Native Method) 03-28 12:11:36.851: E/AndroidRuntime(681): Caused by: java.lang.NullPointerException 03-28 12:11:36.851: E/AndroidRuntime(681): at com.neelrazin.noteit.Password.onCreate(Password.java:57) 03-28 12:11:36.851: E/AndroidRuntime(681): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 03-28 12:11:36.851: E/AndroidRuntime(681): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)

public class Password extends Activity {

    final Context context = this;
     public Long mRowId;
     private NotesDbAdapter mDbHelper;
     String password;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        //setContentView(R.layout.password);


        mRowId = (savedInstanceState == null) ? null :
            (Long) savedInstanceState.getSerializable(NotesDbAdapter.KEY_ROWID);
        if (mRowId == null) {
            Bundle extras = getIntent().getExtras();
            mRowId = extras != null ? extras.getLong(NotesDbAdapter.KEY_ROWID)
                                    : null;
        }

         mDbHelper = new NotesDbAdapter(this);
            mDbHelper.open();
          Cursor notesC = mDbHelper. fetchNote( mRowId);
            startManagingCursor(notesC);
            final String pass = notesC.getString( notesC.getColumnIndex("passw") );


         // custom dialog
            final Dialog dialog = new Dialog(context);
            dialog.setContentView(R.layout.password);
            dialog.setTitle("Enter Password");

            final EditText enterpass = (EditText) dialog.findViewById(R.id.edtext);

            Button ok=(Button)findViewById(R.id.dialogButtonOK);
            ok.setOnClickListener(new View.OnClickListener() {

                @Override
                public void onClick(View v) {
                    // TODO Auto-generated method stub
                    password= enterpass.getText().toString();
                    if(password.equals(pass.toString())){

                        Intent i= new Intent(getBaseContext(),NoteEditor.class);
                          i.putExtra(NotesDbAdapter.KEY_ROWID,mRowId);
                            startActivity(i);
                    }

                }
            });

            Button dialogButton = (Button)          dialog.findViewById(R.id.dialogButtonCANCEL);
            dialogButton.setOnClickListener(new View.OnClickListener() {

                @Override
                public void onClick(View v) {
                    // TODO Auto-generated method stub
                    dialog.dismiss();
                }
            });
            dialog.show();  
    } 

Answer 1

在这里:

Button ok=(Button)findViewById(R.id.dialogButtonOK);//<<

在从 Activity 访问 View 之前，您忘记为 Activity 调用 setContentView。在 Activity 的 onCreate 中将 Activity 的布局设置为:

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

或者如果 dialogBu​​ttonOK 按钮在 Dialog 中，则使用 Dialog 实例将 ok 按钮初始化为:

Button ok=(Button)dialog.findViewById(R.id.dialogButtonOK);