代码里手动编写UI

 protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
//        setContentView(R.layout.activity_main);
        LinearLayout ln=new LinearLayout(this);
        LinearLayout.LayoutParams params=new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);
    //这里调用params.set函数设置布局的属性
        ln.setLayoutParams(params);
        EditText ed=new EditText(this);
        ed.setText("你好世界！");
//        ln.addView(ed);
        ln.addView(ed, params);
//        ln.addView(ed, LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT);
        setContentView(ln);

        }
    }