Working on Android 6.0, ran into the same issue. AlertDialog would default to predefined width set in the theme regardless of the actual width set in the custom view's root Layout. I was able to get it to set properly adjusting the width of the loading_message TextView. Without investigating further, it seems that sizing the actual elements and having the root Layout wrap around them makes it work as expected. Below is an XML layout of a loading dialog which sets width of the the dialog correctly. Using the this library for the animation.

<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:background="@color/custom_color"
    android:padding="@dimen/custom_dimen">
    <com.github.rahatarmanahmed.cpv.CircularProgressView
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:id="@+id/progress_view"
        android:layout_width="40dp"
        android:layout_height="40dp"
        android:layout_centerHorizontal="true"
        app:cpv_color="@color/white"
        app:cpv_animAutostart="true"
        app:cpv_indeterminate="true" />
    <TextView
        android:id="@+id/loading_message"
        android:layout_width="100dp"
        android:layout_height="wrap_content"
        android:layout_below="@+id/progress_view"
        android:layout_centerHorizontal="true"
        android:gravity="center"
        android:textSize="18dp"
        android:layout_marginTop="@dimen/custom_dimen"
        android:textColor="@color/white"
        android:text="@string/custom_string"/>
</RelativeLayout>

这将会非常有效。

@Override
public void onResume() {
    super.onResume();
    Window window = getDialog().getWindow();
    if(window == null) return;
    WindowManager.LayoutParams params = window.getAttributes();
    params.width = 400;
    params.height = 400;
    window.setAttributes(params);
}

下面是在xml中设置DialogFragment宽度/高度的方法。只需要用一个透明背景的框架布局(任何布局都可以)来包装你的viewherarchy。

透明背景似乎是一个特殊的标志，因为当你这样做时，它会自动将framayout的子元素居中。您仍然会在您的片段后面看到全屏变暗，这表明您的片段是活动元素。

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/transparent">

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="300dp"
        android:background="@color/background_material_light">

      .....

我使用AlertDialog创建对话框。所以我在OnShowListener中使用了Rodrigo的答案。

dialog.setOnShowListener(new OnShowListener() {

            @Override
            public void onShow(DialogInterface dialogInterface) {
                Display display = getWindowManager().getDefaultDisplay();
                DisplayMetrics outMetrics = new DisplayMetrics ();
                display.getMetrics(outMetrics);
                dialog.getWindow().setLayout((int)(312 * outMetrics.density), (int)(436 * outMetrics.density));
            }

        });

使用RelativeLayout作为DialogFragment的父元素

我最终覆盖Fragment.onResume()并从底层对话框中抓取属性，然后在那里设置宽度/高度参数。我将最外层的布局高度/宽度设置为match_parent。注意，这段代码似乎也尊重我在xml布局中定义的页边距。

@Override
public void onResume() {
    super.onResume();
    ViewGroup.LayoutParams params = getDialog().getWindow().getAttributes();
    params.width = LayoutParams.MATCH_PARENT;
    params.height = LayoutParams.MATCH_PARENT;
    getDialog().getWindow().setAttributes((android.view.WindowManager.LayoutParams) params);
}