Question

我想从菜单打开警告对话框，在警告对话框中我想要复选框，以便用户可以选择项目，但我得到空指针异常。

         public class MainActivity extends AppCompatActivity
            implements NavigationView.OnNavigationItemSelectedListener {
        AlertDialog.Builder favourite_box;
        CheckBox googlenews,toi,ie,ht

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
            setSupportActionBar(toolbar);

            Initialise_obj();
            checkbox_obj();
        }


        private void checkbox_obj() {
            googlenews=(CheckBox)findViewById(R.id.checkBox1);
            toi=(CheckBox)findViewById(R.id.checkBox2);
            ie=(CheckBox)findViewById(R.id.checkBox3);
            ht=(CheckBox)findViewById(R.id.checkBox4);

        }

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

        @Override
        public boolean onOptionsItemSelected(MenuItem item) {
            // Handle action bar item clicks here. The action bar will
            // automatically handle clicks on the Home/Up button, so long
            // as you specify a parent activity in AndroidManifest.xml.
            int id = item.getItemId();

            if (id == R.id.action_fav_list) {
                LayoutInflater inflater = this.getLayoutInflater();
                View dialogView = inflater.inflate(R.layout.favourite_dialog, null);

                favourite_box = new AlertDialog.Builder(this);
                favourite_box.setView(dialogView);
                //   historyBox.setMessage("message to be display in alert box");
                favourite_box.setPositiveButton("Done", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {


                        if(googlenews.isChecked()){
                            Toast.makeText(getApplicationContext(),"haha",Toast.LENGTH_SHORT).show();
                        } if(toi.isChecked()){
                           Toast.makeText(getApplicationContext(),"done",Toast.LENGTH_SHORT).show();
                        } if(ie.isChecked()){
                            Toast.makeText(getApplicationContext(),"completed",Toast.LENGTH_SHORT).show();
                        } if(ht.isChecked()){
    Toast.makeText(getApplicationContext(),"success",Toast.LENGTH_SHORT).show();
                        } 

                        dialog.cancel();
                    }
                });
                favourite_box.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        dialog.cancel();
                    }
                });

                final AlertDialog alert=favourite_box.create();
                alert.setTitle("Favourite");
                alert.show();

            }

            return super.onOptionsItemSelected(item);
        }


    }

E / AndroidRuntime：致命异常：主要过程：com.example.kishan.bulletin，PID：24928 java.lang.NullPointerException：尝试调用虚方法＆＃39; boolean android.widget.CheckBox.isChecked（）＆＃39;在null对象引用上在com.example.kishan.bulletin.MainActivity $ 2 $ override.onClick（MainActivity.java:206）在com.example.kishan.bulletin.MainActivity $ 2 $ override.access $ dispatch（MainActivity.java）在com.example.kishan.bulletin.MainActivity $ 2.onClick（MainActivity.java:0）在android.support.v7.app.AlertController $ ButtonHandler.handleMessage（AlertController.java:157）在android.os.Handler.dispatchMessage（Handler.java:111）在android.os.Looper.loop（Looper.java:207）在android.app.ActivityThread.main（ActivityThread.java:5769） at java.lang.reflect.Method.invoke（Native Method）在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:789）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:679）

Answer 1

请勿在{{1}}中调用checkbox_obj()方法。从onCreate()移除方法调用并删除方法onCreate()。

您必须从对话框布局中获取复选框视图。你必须这样做。我已将checkbox_obj()

中的复选框初始化

onOptionsItemSelected()

想在android中的警告对话框中使用复选框

1 个答案: