效果图：

代码直通车

BottomSheetDialogFragment类继承关系：

BottomSheetDialogFragment -> AppCompatDialogFragment -> DialogFragment -> Fragment

在实际创建的BottomSheetDialog中看到引用的布局文件，引用的是id为design_bottom_sheet的FrameLayout，可以通过设置它的高度来修改dialog的高度。

    private View wrapInBottomSheet(int layoutResId, View view, LayoutParams params) {
        FrameLayout container = (FrameLayout)View.inflate(this.getContext(), layout.design_bottom_sheet_dialog, (ViewGroup)null);
        CoordinatorLayout coordinator = (CoordinatorLayout)container.findViewById(id.coordinator);
        if (layoutResId != 0 && view == null) {
            view = this.getLayoutInflater().inflate(layoutResId, coordinator, false);
        }

        FrameLayout bottomSheet = (FrameLayout)coordinator.findViewById(id.design_bottom_sheet);
        this.behavior = BottomSheetBehavior.from(bottomSheet);
        this.behavior.setBottomSheetCallback(this.bottomSheetCallback);
        this.behavior.setHideable(this.cancelable);
        if (params == null) {
            bottomSheet.addView(view);
        } else {
            bottomSheet.addView(view, params);
        }

        coordinator.findViewById(id.touch_outside).setOnClickListener(new OnClickListener() {
            public void onClick(View view) {
                if (BottomSheetDialog.this.cancelable && BottomSheetDialog.this.isShowing() && BottomSheetDialog.this.shouldWindowCloseOnTouchOutside()) {
                    BottomSheetDialog.this.cancel();
                }

            }
        });
        ViewCompat.setAccessibilityDelegate(bottomSheet, new AccessibilityDelegateCompat() {
            public void onInitializeAccessibilityNodeInfo(View host, AccessibilityNodeInfoCompat info) {
                super.onInitializeAccessibilityNodeInfo(host, info);
                if (BottomSheetDialog.this.cancelable) {
                    info.addAction(1048576);
                    info.setDismissable(true);
                } else {
                    info.setDismissable(false);
                }

            }

            public boolean performAccessibilityAction(View host, int action, Bundle args) {
                if (action == 1048576 && BottomSheetDialog.this.cancelable) {
                    BottomSheetDialog.this.cancel();
                    return true;
                } else {
                    return super.performAccessibilityAction(host, action, args);
                }
            }
        });
        bottomSheet.setOnTouchListener(new OnTouchListener() {
            public boolean onTouch(View view, MotionEvent event) {
                return true;
            }
        });
        return container;
    }

创建简单的BottomSheetDialogFragment的基类，设置自定义弹框的高度。重写DialogFragment的getTheme()方法来设置弹框的style。

public class BaseBottomSheetDialog extends BottomSheetDialogFragment {
    private FrameLayout bottomSheet;
    public BottomSheetBehavior<FrameLayout> behavior;

    @Override
    public void onStart() {
        super.onStart();

        BottomSheetDialog dialog = (BottomSheetDialog) getDialog();
        bottomSheet = dialog.getDelegate().findViewById(android.support.design.R.id.design_bottom_sheet);
        if (bottomSheet != null) {
            CoordinatorLayout.LayoutParams layoutParams = (CoordinatorLayout.LayoutParams) bottomSheet.getLayoutParams();
            layoutParams.height = getHeight();
            bottomSheet.setLayoutParams(layoutParams);
            behavior = BottomSheetBehavior.from(bottomSheet);
            behavior.setPeekHeight(getHeight());
            // 初始为展开状态
            behavior.setState(BottomSheetBehavior.STATE_EXPANDED);
        }
    }

    @Override
    public int getTheme() {
        return R.style.basedialog_anim_style;
    }

    protected int getHeight() {
        return getResources().getDisplayMetrics().heightPixels;
    }

}

子类继承使用：

public class MyBottomSheetDialog extends BaseBottomSheetDialog {

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.dialog_comment, container);
        return view;
    }

    @Override
    protected int getHeight() {
        return getResources().getDisplayMetrics().heightPixels - 400;
    }
}

展示方式：

        MyBottomSheetDialog dialog = new MyBottomSheetDialog();
        dialog.show(getSupportFragmentManager(), "");