Android布局代码实现

布局不一定只能写 XML。用 LayoutInflater 把 XML 灌成 View，或纯代码 new 出 LinearLayout / RelativeLayout，都能在运行时拼界面。关键是 inflate(resource, root, attachToRoot) 三个参数怎么配合。

一、LayoutInflater 三参数

先拿到 Inflater，再 inflate：

LayoutInflater mInflater = LayoutInflater.from(context);
ViewGroup parent;
View v = mInflater.inflate(R.layout.item_simpleadapter_view, parent, true);
View v = mInflater.inflate(R.layout.item_simpleadapter_view, parent, false);
View v = mInflater.inflate(R.layout.item_simpleadapter_view, null);

对应签名：public View inflate(int resourceId, ViewGroup root, boolean attachToRoot)

二、代码实现线性布局

new 一个垂直 LinearLayout，铺满父布局，再 add 两个 TextView，最后 setContentView：

public void setLinearLayout() {
  LinearLayout linearLayout = new LinearLayout(this);
  linearLayout.setOrientation(LinearLayout.VERTICAL);

  LayoutParams layoutParams = new LinearLayout.LayoutParams(
      LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);
  linearLayout.setLayoutParams(layoutParams);

  TextView textView = new TextView(this);
  textView.setGravity(Gravity.CENTER);
  textView.setText("子元素0");
  textView.setTextSize(20);
  textView.setBackgroundColor(R.color.myblue);
  textView.setLayoutParams(new LinearLayout.LayoutParams(
      LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT));

  TextView textView1 = new TextView(this);
  textView1.setGravity(Gravity.CENTER);
  textView1.setText("子元素1");
  textView1.setTextSize(20);
  textView1.setBackgroundColor(Color.BLUE);
  textView1.setLayoutParams(new LinearLayout.LayoutParams(
      LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT));

  linearLayout.addView(textView);
  linearLayout.addView(textView1);
  setContentView(linearLayout);
}

三、代码实现相对布局

RelativeLayout 靠 addRule 描述谁在谁上、谁对齐谁。下面四个按钮：btn1 顶栏水平居中；btn2 在其下且左对齐；btn3 在 btn1 下方、btn2 右侧并右对齐 btn1；btn4 在 btn2 下方水平居中。

public void setRelationLayout() {
  RelativeLayout rl = new RelativeLayout(this);

  Button btn1 = new Button(this);
  btn1.setText("----------1------------");
  btn1.setId(1);
  RelativeLayout.LayoutParams lp1 = new RelativeLayout.LayoutParams(
      ViewGroup.LayoutParams.WRAP_CONTENT,
      ViewGroup.LayoutParams.WRAP_CONTENT);
  lp1.addRule(RelativeLayout.ALIGN_PARENT_TOP);
  lp1.addRule(RelativeLayout.CENTER_HORIZONTAL, RelativeLayout.TRUE);
  // btn1 位于父 View 顶部，水平居中
  rl.addView(btn1, lp1);

  Button btn2 = new Button(this);
  btn2.setText("|\n|\n2\n|\n|\n|");
  btn2.setId(2);
  RelativeLayout.LayoutParams lp2 = new RelativeLayout.LayoutParams(
      ViewGroup.LayoutParams.WRAP_CONTENT,
      ViewGroup.LayoutParams.WRAP_CONTENT);
  lp2.addRule(RelativeLayout.BELOW, 1);
  lp2.addRule(RelativeLayout.ALIGN_LEFT, 1);
  // btn2 在 btn1 下方，左边与 btn1 对齐
  rl.addView(btn2, lp2);

  Button btn3 = new Button(this);
  btn3.setText("|\n|\n3\n|\n|\n|");
  btn3.setId(3);
  RelativeLayout.LayoutParams lp3 = new RelativeLayout.LayoutParams(
      ViewGroup.LayoutParams.WRAP_CONTENT,
      ViewGroup.LayoutParams.WRAP_CONTENT);
  lp3.addRule(RelativeLayout.BELOW, 1);
  lp3.addRule(RelativeLayout.RIGHT_OF, 2);
  lp3.addRule(RelativeLayout.ALIGN_RIGHT, 1);
  // btn3 在 btn1 下方、btn2 右方，右边与 btn1 对齐（会拉宽）
  rl.addView(btn3, lp3);

  Button btn4 = new Button(this);
  btn4.setText("-----------------4--------------");
  btn4.setId(4);
  RelativeLayout.LayoutParams lp4 = new RelativeLayout.LayoutParams(
      ViewGroup.LayoutParams.WRAP_CONTENT,
      ViewGroup.LayoutParams.WRAP_CONTENT);
  lp4.addRule(RelativeLayout.BELOW, 2);
  lp4.addRule(RelativeLayout.CENTER_HORIZONTAL, RelativeLayout.TRUE);
  // btn4 在 btn2 下方，父布局中水平居中
  rl.addView(btn4, lp4);

  setContentView(rl);
}

一句话总结：inflate 时 root + attachToRoot 决定「只借 LayoutParams」还是「直接挂到父布局」；纯代码布局则是 new 容器、设 LayoutParams、addView，最后 setContentView。