问android再次运行代码时出现异常

EN

public class MainActivity extends FragmentActivity {

    ImageView iview1;
    LayoutParams params;
    FragmentManager fmgr;
    FragmentTransaction ftr;
    FirstFragment ff;
    LinearLayout layout;
    ArrayList<Fragment> FArray;
    int counter;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        counter=0;
        FArray=new ArrayList<Fragment>();
        iview1=(ImageView)findViewById(R.id.iview);
        iview1.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View arg0) {
                // TODO Auto-generated method stub

                showFF();

            }
        });
        layout=(LinearLayout) findViewById(R.id.frag);
        fmgr = getSupportFragmentManager();
        ftr=fmgr.beginTransaction();

        params=(LayoutParams) layout.getLayoutParams();

        //showF();
    }

    public void showFF(){
        FArray.add(new FirstFragment());
        ftr.add(R.id.frag, FArray.get(counter));
        if (true){//showing==false){
            params.weight=1;
            iview1.setLayoutParams(params);
            layout.setLayoutParams(params);
            ftr.commit();
        }
        counter++;

    }
}