无法在运行时创建editText

Question

当用户将焦点放在视图上时，我想添加三个相邻的editText。此外，我希望当用户点击第一个editText时，在现有的editText下面创建一组新的3个editText。

此代码返回错误（nullPointerException）

 @Override
public void onFocusChange(View v, boolean hasFocus) {
    // TODO Auto-generated method stub
    switch(v.getId()){
    // 5 is the id of the view
    case 5:
        main=new RelativeLayout(this);
        mainParams=new RelativeLayout.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT );
        main.setLayoutParams(mainParams);
        //mainLayout is a LinearLayout

        items[no]=new EditText(this);
        rates[no]=new EditText(this);
        quants[no]=new EditText(this);
        items[no].setHint("Enter item name");
        rates[no].setHint("Rate");
        quants[no].setHint("Quantity");
        items[no].setId(id++);
        rates[no].setId(id++);
        quants[no].setId(id++);
        RelativeLayout.LayoutParams etParams=new RelativeLayout.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
        RelativeLayout.LayoutParams rParams=new RelativeLayout.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);

        etParams.addRule(RelativeLayout.ALIGN_PARENT_LEFT);
        rParams.addRule(RelativeLayout.ALIGN_RIGHT);

        items[no].setLayoutParams(etParams);
        rates[no].setLayoutParams(rParams);
        quants[no].setLayoutParams(rParams);
        mainLayout.addView(main);
        no++;
    }

Answer 1

试试这个，

// 5 is the id of the view
    case 5:
        main=new RelativeLayout(this);
        mainParams=new RelativeLayout.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT );
        main.setLayoutParams(mainParams);
        //mainLayout is a LinearLayout

        items[no]=new EditText(this);
        rates[no]=new EditText(this);
        quants[no]=new EditText(this);

        RelativeLayout.LayoutParams etParams=new RelativeLayout.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
        RelativeLayout.LayoutParams rParams=new RelativeLayout.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);

        etParams.addRule(RelativeLayout.ALIGN_PARENT_LEFT);
        rParams.addRule(RelativeLayout.ALIGN_RIGHT);

        items[no].setLayoutParams(etParams);
        rates[no].setLayoutParams(rParams);
        quants[no].setLayoutParams(rParams);
        mainLayout.addView(main);
 items[no].setHint("Enter item name");
        rates[no].setHint("Rate");
        quants[no].setHint("Quantity");
        items[no].setId(id++);
        rates[no].setId(id++);
        quants[no].setId(id++);
        no++;
    }