java 一个FrameLayout，可以一次显示一个不同的状态。

Posted 2021-05-08

/**
 * A {@link FrameLayout} that can show different states one at a time.
 */
public class StateFrameLayout extends ViewAnimator {
  public static final String STATE_LOADING = "loading";
  public static final String STATE_EMPTY = "empty";
  public static final String STATE_ERROR = "error";
  private static final String STATE_DEFAULT = "default";

  private SimpleArrayMap<String, View> stateViewMap;

  public StateFrameLayout(Context context) {
    super(context);
    init();
  }

  public StateFrameLayout(Context context, AttributeSet attrs) {
    super(context, attrs);
    init();
  }

  /**
   * Shows the given state and hides the current state.
   */
  public void showState(String state) {
    View view = stateViewMap.get(state);

    if (view.getVisibility() == View.VISIBLE) {
      return;
    }

    setDisplayedChild(indexOfChild(view));
  }

  /**
   * Alias for {@link #showState(String)} with STATE_DEFAULT as the parameter.
   */
  public void reset() {
    showState(STATE_DEFAULT);
  }

  /**
   * Registers the given View as the content view for this layout. By default,
   * this layout will select its first child as the content view. This method
   * will override that behavior.
   */
  public void setContentView(View view) {
    stateViewMap.put(STATE_DEFAULT, view);
  }

  /**
   * Assigns the given View to the given State and adds the View to the view
   * hierarchy.
   */
  public void setState(String state, View view) {
    // If state already exists, it means a view already exists for this
    // state. Therefore, we need to remove that existing view from the view
    // hierarchy.
    if (stateViewMap.containsKey(state)) {
      View existingView = stateViewMap.get(state);
      removeView(existingView);
    }

    stateViewMap.put(state, view);
    view.setVisibility(View.GONE);
    addView(view);
  }

  /**
   * Returns the view associated with the given state
   */
  public View getViewForState(String state) {
    return stateViewMap.get(state);
  }

  @Override protected void onAttachedToWindow() {
    super.onAttachedToWindow();
    if (getChildCount() > 0) {
      setContentView(getChildAt(0));
    }
  }

  @Override protected void onDetachedFromWindow() {
    super.onDetachedFromWindow();
    stateViewMap.clear();
  }

  private void init() {
    stateViewMap = new SimpleArrayMap<>();
    Animation in = new AlphaAnimation(0, 1);
    in.setDuration(150);
    setInAnimation(in);

    Animation out = new AlphaAnimation(1, 0);
    out.setDuration(150);
    setOutAnimation(out);
    
    // Ensure that this FrameLayout only measures child views that are View.VISIBLE or View.INVISIBLE.
    setMeasureAllChildren(false);
  }
}