android - 以编程方式将 ProgressBar 放在屏幕的中心

Question

我正在创建一个扩展 LinearLayout 的类。因为我正在尝试以编程方式进行布局。这是我到目前为止所做的:

RelativeLayout.LayoutParams parentParam = new RelativeLayout.LayoutParams(
            RelativeLayout.LayoutParams.MATCH_PARENT,
            RelativeLayout.LayoutParams.MATCH_PARENT);

    this.setLayoutParams(parentParam);
    this.setOrientation(LinearLayout.VERTICAL);

    WebView webView = new WebView(context);
    LinearLayout.LayoutParams webViewParam = new LinearLayout.LayoutParams(
            LinearLayout.LayoutParams.MATCH_PARENT,
            LinearLayout.LayoutParams.MATCH_PARENT);

    webView.setLayoutParams(webViewParam);
    this.addView(webView);

    pb = new ProgressBar(context);
    LinearLayout.LayoutParams pbParam = new LinearLayout.LayoutParams(
            LinearLayout.LayoutParams.WRAP_CONTENT,
            LinearLayout.LayoutParams.WRAP_CONTENT);
    pbParam.gravity = Gravity.CENTER_HORIZONTAL | Gravity.CENTER_VERTICAL;
    pb.setLayoutParams(pbParam);
    webView.addView(pb);

我的所有东西都工作正常，WebView 和 ProgressBar 是可见的并在那里执行相应的任务，但我正在尝试将 ProgressBar在屏幕的 CENTER 中。

我在这里错过了什么。任何类型的输入都将不胜感激。

编辑:现在的输出看起来像这样:

Answer 1

这是我将 ProgressBar 置于中心所做的工作。为了我的目的，我使用了 ScrollView。这是我使用的代码:

RelativeLayout.LayoutParams parentParam = new RelativeLayout.LayoutParams(
            RelativeLayout.LayoutParams.MATCH_PARENT,
            RelativeLayout.LayoutParams.MATCH_PARENT);

    this.setLayoutParams(parentParam);
    this.setOrientation(LinearLayout.VERTICAL);

    scrollView = new ScrollView(context);
    scrollView.setLayoutParams(new FrameLayout.LayoutParams(
            FrameLayout.LayoutParams.MATCH_PARENT,
            FrameLayout.LayoutParams.MATCH_PARENT,
            Gravity.CENTER_HORIZONTAL | Gravity.CENTER_VERTICAL));
    scrollView.setFillViewport(true);

    scrollView.setBackgroundColor(Color.TRANSPARENT);

    pb = new ProgressBar(context);
    LinearLayout.LayoutParams pbParam = new LinearLayout.LayoutParams(
            LinearLayout.LayoutParams.WRAP_CONTENT,
            LinearLayout.LayoutParams.WRAP_CONTENT);
    pb.setLayoutParams(pbParam);

    RelativeLayout rel = new RelativeLayout(context);
    RelativeLayout.LayoutParams relParam = new RelativeLayout.LayoutParams(
            RelativeLayout.LayoutParams.WRAP_CONTENT,
            RelativeLayout.LayoutParams.WRAP_CONTENT);
    relParam.addRule(RelativeLayout.CENTER_IN_PARENT);
    rel.addView(pb, relParam);

    scrollView.addView(rel);

    webView = new WebView(context);
    LinearLayout.LayoutParams webViewParam = new LinearLayout.LayoutParams(
            LinearLayout.LayoutParams.MATCH_PARENT,
            LinearLayout.LayoutParams.MATCH_PARENT);
    webViewParam.gravity = Gravity.CENTER_HORIZONTAL
            | Gravity.CENTER_VERTICAL;
    webView.setLayoutParams(webViewParam);

    this.addView(scrollView);

    this.addView(webView);  

希望，这会对正在尝试同样事情的其他人有所帮助。