用JAVA代码为android应用添加一个按钮

LinearLayout layout = new LinearLayout(ActivityRegisterCity.this);
layout.setOrientation(LinearLayout.VERTICAL);
layout.setPadding(0, 0, 0, 0);
layout.setLayoutParams(new
ViewGroup.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT,
ViewGroup.LayoutParams.WRAP_CONTENT));
Button btn = new Button(ActivityRegisterCity.this);
LinearLayout.LayoutParams params = new
LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT,
LinearLayout.LayoutParams.WRAP_CONTENT);
params.setMargins(0, 0, 0, 0);
btn.setLayoutParams(params);
layout.addView(btn);
setContentView(layout);