我把@rmirabella的回答也更新了一下，让它也能处理身高问题:

private fun DialogFragment.setSize(widthPercentage: Int, heightPercentage: Int) {
    val newWidth = widthPercentage.toFloat() / 100
    val newHeight = heightPercentage.toFloat() / 100
    val dm = Resources.getSystem().displayMetrics
    val rect = dm.run { Rect(0, 0, widthPixels, heightPixels) }
    val percentWidth = rect.width() * newWidth
    val percentHeight = rect.height() * newHeight
    dialog?.window?.setLayout(percentWidth.toInt(), percentHeight.toInt())
}

然后在你的DialogFragment中或onStart()之后:

override fun onStart() {
    super.onStart()
    setSize(
        widthPercentage = 100,
        heightPercentage = 80
    )
}

这里是kotlin版本

    override fun onResume() {
        super.onResume()

        val params:ViewGroup.LayoutParams = dialog.window.attributes
        params.width = LinearLayout.LayoutParams.MATCH_PARENT
        params.height = LinearLayout.LayoutParams.MATCH_PARENT
        dialog.window.attributes = params as android.view.WindowManager.LayoutParams
    }

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);
}

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>

public void onResume() {

    Window window = Objects.requireNonNull(getDialog()).getWindow();
    Point size = new Point();
    assert window != null;
    Display display = window.getWindowManager().getDefaultDisplay();
    display.getSize(size);
    window.setLayout( (int)(size.x * 0.9), (int) (size.y * 0.75));
    window.setGravity( Gravity.CENTER );
    super.onResume();
    

}

添加到FragmentDialog:

public void onResume() {
    Window window = getDialog().getWindow();
    Point size = new Point();
    Display display = window.getWindowManager().getDefaultDisplay();
    display.getSize(size);
    window.setLayout( (int)(size.x * 0.9), WindowManager.LayoutParams.WRAP_CONTENT );
    window.setGravity( Gravity.CENTER );
    super.onResume();
}