Android 动态改变布局实例详解

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:tools="http://schemas.android.com/tools"
  android:id="@+id/root"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:padding="20dp"
  tools:context="${packageName}.${activityClass}" >

  <RelativeLayout
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true" >

    <ImageView
      android:id="@+id/logo"
      android:layout_width="150dp"
      android:layout_height="150dp"
      android:layout_centerHorizontal="true"
      android:scaleType="centerCrop"
      android:src="@drawable/ic_launcher"
      tools:ignore="ContentDescription" />

    <TextView
      android:id="@+id/label"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_below="@id/logo"
      android:layout_centerHorizontal="true"
      android:layout_marginLeft="10dp"
      android:layout_marginTop="10dp"
      android:text="@string/hello_world"
      android:textSize="20sp" />
  </RelativeLayout>

  <EditText
    android:id="@+id/input"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_below="@id/container"
    android:layout_margin="16dp"
    android:hint="Input sth."
    tools:ignore="HardcodedText" />

</RelativeLayout>

public class MainActivity extends Activity {

  private View root; // 最外层布局
  private View logo; // Logo图标
  private View label; // Logo附近的文字

  private int rootBottom = Integer.MIN_VALUE;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    root = findViewById(R.id.root);
    logo = findViewById(R.id.logo);
    label = findViewById(R.id.label);
    root.getViewTreeObserver().addOnGlobalLayoutListener(new OnGlobalLayoutListener() {

      @Override
      public void onGlobalLayout() {
        Rect r = new Rect();
        root.getGlobalVisibleRect(r);
        // 进入Activity时会布局，第一次调用onGlobalLayout，先记录开始软键盘没有弹出时底部的位置
        if (rootBottom == Integer.MIN_VALUE) {
          rootBottom = r.bottom;
          return;
        }
        // adjustResize，软键盘弹出后高度会变小
        if (r.bottom < rootBottom) {
          RelativeLayout.LayoutParams lp = (LayoutParams) logo.getLayoutParams();
          // 如果Logo不是水平居中，说明是因为接下来的改变Logo大小位置导致的再次布局，忽略掉，否则无限循环
          if (lp.getRules()[RelativeLayout.CENTER_HORIZONTAL] != 0) {
            // Logo显示到左上角
            lp.addRule(RelativeLayout.CENTER_HORIZONTAL, 0); // 取消水平居中
            lp.addRule(RelativeLayout.ALIGN_PARENT_LEFT); // 左对齐

            // 缩小Logo为1/2
            int height = logo.getHeight(); // getMeasuredHeight()
            int width = logo.getWidth();
            lp.width = width / 2;
            lp.height = height / 2;
            logo.setLayoutParams(lp);

            // Logo下的文字
            RelativeLayout.LayoutParams labelParams = (LayoutParams) label.getLayoutParams();
            labelParams.addRule(RelativeLayout.CENTER_HORIZONTAL, 0); // 取消水平居中
            labelParams.addRule(RelativeLayout.BELOW, 0); // 取消显示到logo的下方
            labelParams.addRule(RelativeLayout.RIGHT_OF, R.id.logo); // 显示到Logo的右方
            labelParams.addRule(RelativeLayout.CENTER_VERTICAL); // 垂直居中
            label.setLayoutParams(labelParams);
          }
        } else { // 软键盘收起或初始化时
          RelativeLayout.LayoutParams lp = (LayoutParams) logo.getLayoutParams();
          // 如果没有水平居中，说明是软键盘收起，否则是开始时的初始化或者因为此处if条件里的语句修改控件导致的再次布局，忽略掉，否则无限循环
          if (lp.getRules()[RelativeLayout.CENTER_HORIZONTAL] == 0) {
            // 居中Logo
            lp.addRule(RelativeLayout.CENTER_HORIZONTAL);
            lp.addRule(RelativeLayout.ALIGN_PARENT_LEFT, 0);

            // 还原Logo为原来大小
            int height = logo.getHeight();
            int width = logo.getWidth();
            lp.width = width * 2;
            lp.height = height * 2;
            logo.setLayoutParams(lp);

            // Logo下的文字
            RelativeLayout.LayoutParams labelParams = (LayoutParams) label.getLayoutParams();
            labelParams.addRule(RelativeLayout.CENTER_HORIZONTAL); // 设置水平居中
            labelParams.addRule(RelativeLayout.BELOW, R.id.logo); // 设置显示到Logo下面
            labelParams.addRule(RelativeLayout.RIGHT_OF, 0); // 取消显示到Logo右面
            labelParams.addRule(RelativeLayout.CENTER_VERTICAL, 0); // 取消垂直居中
            label.setLayoutParams(labelParams);
          }
        }
      }
    });
  }
}

public static final int TRUE = -1;

public void addRule(int verb) {
  mRules[verb] = TRUE;
  mInitialRules[verb] = TRUE;
  mRulesChanged = true;
}

public void addRule(int verb, int anchor) {
  mRules[verb] = anchor;
  mInitialRules[verb] = anchor;
  mRulesChanged = true;
}

public void removeRule(int verb) {
  mRules[verb] = 0;
  mInitialRules[verb] = 0;
  mRulesChanged = true;
 }