以编程方式以线性布局滚动视图

Question

I'm trying to make my linearLayout scrollable programmatically but it doesnt work. Im just new in android so pls be nice tnx!..

full code

  ScrollView scrollView= new ScrollView(this);
                LinearLayout mainLayout= new LinearLayout(this);
                mainLayout.setOrientation(LinearLayout.VERTICAL);

                for (int i = 1; i <= 20; i++) {
                    LinearLayout linearLayout = new LinearLayout(this);
                    linearLayout.setOrientation(LinearLayout.HORIZONTAL);
                    linearLayout.setTag(i);
                    Button btn1 = new Button(this);
                    btn1.setId(i);
                    final int id_ = btn1.getId();
                    btn1.setText("button " + id_);

                   btn1 = ((Button) findViewById(id_));
                    btn1.setOnClickListener(new View.OnClickListener() {
                        public void onClick(View view) {
                            Toast.makeText(view.getContext(),
                                    "Button 1 clicked index = " + id_, Toast.LENGTH_SHORT)
                                    .show();
                        }
                    }); 
                  linearLayout.addView(btn1);
                   mainLayout.addView(linearLayout);


                }
                 scrollView.addView(mainLayout);
                    setContentView(scrollView);

Error stack trace

Answer 1

The issue is btn1 = ((Button) findViewById(id_));

This should look like btn1 = (Button) findViewById(R.id.whatever_your_id_is_in_xml);

Because you don't supply an id it never finds your button, so btn1 is null when you try to set the listener

(find view is looking in the xml / root view for this id, you dont need to do this - you already have the button because you created it programmatically)

Edit

The solution in your case is simply to remove this line compeltely: btn1 = ((Button) findViewById(id_));