Android DialogFragment 實現抽屜效果：BottomSheetDialogFragment 最佳實踐

需求分析

• 從底部滑入，手指水平拖動可看到底下 Activity
• 解決 show() 時機導致的 IllegalStateException: Can not perform this action after onSaveInstanceState

推薦方案：BottomSheetDialogFragment (Material Design)

public class BottomSheetFragment extends BottomSheetDialogFragment {
    
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
                             Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_bottom_sheet, container, false);
        // 設定拖動行為
        return view;
    }

    @Override
    public void onStart() {
        super.onStart();
        BottomSheetDialog dialog = (BottomSheetDialog) getDialog();
        if (dialog != null) {
            FrameLayout bottomSheet = dialog.findViewById(com.google.android.material.R.id.design_bottom_sheet);
            BottomSheetBehavior behavior = BottomSheetBehavior.from(bottomSheet);
            behavior.setState(BottomSheetBehavior.STATE_EXPANDED);
            behavior.setDraggable(true);  // 允許拖動關閉
        }
    }
}

安全顯示模式（避免 onSaveInstanceState 崩潰）

// 錯誤寫法
fragment.show(getSupportFragmentManager(), "tag");

// 正確寫法 1：commitAllowingStateLoss
fragment.show(getSupportFragmentManager().beginTransaction(), "tag");

// 正確寫法 2：Lifecycle 感知 (Fragment 1.3.0+)
fragment.show(getChildFragmentManager(), "tag");  // 在 Fragment 內使用

// 正確寫法 3：延遲顯示
new Handler(Looper.getMainLooper()).post(() -> 
    fragment.show(getSupportFragmentManager(), "tag")
);

自訂 DialogFragment 抽屜效果（不依賴 Material 元件）

@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setStyle(DialogFragment.STYLE_NORMAL, R.style.BottomSheetDialogTheme);
}

@Override
public void onStart() {
    super.onStart();
    Dialog dialog = getDialog();
    if (dialog != null) {
        Window window = dialog.getWindow();
        WindowManager.LayoutParams params = window.getAttributes();
        params.gravity = Gravity.BOTTOM;
        params.width = WindowManager.LayoutParams.MATCH_PARENT;
        params.height = WindowManager.LayoutParams.WRAP_CONTENT;
        window.setAttributes(params);
        window.setWindowAnimations(R.style.BottomSheetAnimation);
    }
}

styles.xml 關鍵設定