Builder 建構者模式 | 實現與解說 | Android Framwrok Dialog 視窗

可以透過 Java Package 的特性，將 Product 限制在 Package 內，並透過建構函數限制... 等等技術（請參考以下範例）

:::info

● 通常對於生產出的產品，我們也會希望它不會受到使用者 setting 而影響到產品的功能（就是生產出啥，使用者就用啥）；

但相對的，使用者需要直接操控到 Builder

public interface ComputerBuilder_2<T extends Computer_2> {

    ComputerBuilder_2<T> setBoard(String board);
    ComputerBuilder_2<T> setCPU(String cpu);
    ComputerBuilder_2<T> setPower(int power);

    String getBoard();
    String getCpu();
    int getPower();

    T create();

}

// Builder 實作類

public class Giga implements ComputerBuilder_2<Computer_2> {

    private String cpu;
    private String board;
    private int power;

    public Giga(String cpu, String board) {
        this.cpu = cpu;
        this.board = board;
    }

    @Override
    public ComputerBuilder_2<Computer_2> setBoard(String board) {
        this.board = board + "_version_2";
        return this;
    }

    @Override
    public ComputerBuilder_2<Computer_2> setCPU(String cpu) {
        this.cpu = cpu + "_version_2";
        return this;
    }

    @Override
    public ComputerBuilder_2<Computer_2> setPower(int power) {
        this.power = power;
        return this;
    }

    @Override
    public String getBoard() {
        return board;
    }

    @Override
    public String getCpu() {
        return cpu;
    }

    @Override
    public int getPower() {
        return power;
    }

    @Override
    public Computer_2 create() {
        if(power <= 0) {
            this.power = 300;
        }
        
        // 傳入自身
        return new Computer_2(this);
    }
}

● 限制 Scope：將 Computer_2 類移動到與 ComputerBuilder_2 相同資料夾，透過 Package 限制其他類對 Computer_2 的訪問

● 限制建構函數：設定 Computer_2 constructor 建構函數，參數為 ComputerBuilder_2

● 限制設定：讓 Computer_2 類單純化，變成一個資料獲取點 (只有 getter)

// Product

public class Computer_2 {
    private String board;
    private String cpu;
    private int power;

    public Computer_2(ComputerBuilder_2<?> builder) {
        board = builder.getBoard();
        cpu = builder.getCpu();
        power = builder.getPower();
    }

    void setBoard(String board) {
        this.board = board;
    }

    void setCPU(String cpu) {
        this.cpu = cpu;
    }

    void setPower(int power) {
        this.power = power;
    }

    public void print() {
        System.out.println("CPU is " + cpu + "\n"
                +"Board is " + board + "\n"
                +"power is " + power + "w\n"
        );
    }
}

針對變形 Builder 修正，UML 圖也需要做部分調整；可以看到 Product 與 Builder 關係更加緊密 (聚合)

// AlertDialog.java

public class AlertDialog extends Dialog implements DialogInterface {

    // 內部 Builder 類
    public static class Builder {
        // 參數儲存
        private final AlertController.AlertParams P;

        public Builder(Context context, int themeResId) {
            // 創建參數倉庫 AlertParams
            P = new AlertController.AlertParams(new ContextThemeWrapper(
                    context, resolveDialogTheme(context, themeResId)));
        }


        public Builder setTitle(@StringRes int titleId) {
            P.mTitle = P.mContext.getText(titleId);
            return this;
        }

        public Builder setCustomTitle(View customTitleView) {
            P.mCustomTitleView = customTitleView;
            return this;
        }

        public Builder setMessage(CharSequence message) {
            P.mMessage = message;
            return this;
        }

        public Builder setIcon(@DrawableRes int iconId) {
            P.mIconId = iconId;
            return this;
        }   

        ...

        // 創建目標物件，並設定到 AlerDialog 中
        public AlertDialog create() {
            // Context has already been wrapped with the appropriate theme.
            final AlertDialog dialog = new AlertDialog(P.mContext, 0, false);

            // @ 追蹤 apply 方法
            P.apply(dialog.mAlert);
            dialog.setCancelable(P.mCancelable);
            if (P.mCancelable) {
                dialog.setCanceledOnTouchOutside(true);
            }
            dialog.setOnCancelListener(P.mOnCancelListener);
            dialog.setOnDismissListener(P.mOnDismissListener);
            if (P.mOnKeyListener != null) {
                dialog.setOnKeyListener(P.mOnKeyListener);
            }
            return dialog;
        }

        // 創建並展示
        public AlertDialog show() {
            final AlertDialog dialog = create();
            dialog.show();
            return dialog;
        }
    }
}

// AlertDialog.java

public class AlertDialog extends Dialog implements DialogInterface {

    // AlierDialog 與 AlertController 產生關聯
    private AlertController mAlert;

    protected AlertDialog(Context context, @StyleRes int themeResId) {
        this(context, themeResId, true);
    }

    // 用 package 限制 constructor
    AlertDialog(Context context, @StyleRes int themeResId, boolean createContextThemeWrapper) {
        super(context, createContextThemeWrapper ? resolveDialogTheme(context, themeResId) : 0,
                createContextThemeWrapper);

        ...
        // 創建 AlertController
        mAlert = AlertController.create(getContext(), this, getWindow());
    }

    @Override
    public void setTitle(CharSequence title) {
        super.setTitle(title);
        mAlert.setTitle(title);
    }

    public void setCustomTitle(View customTitleView) {
        mAlert.setCustomTitle(customTitleView);
    }

    public void setMessage(CharSequence message) {
        mAlert.setMessage(message);
    }

    public void setView(View view) {
        mAlert.setView(view);
    }

    public void setIcon(Drawable icon) {
        mAlert.setIcon(icon);
    }

    ...

}

// AlertController.java

public class AlertController {

    /**
     * AlertController#AlertParams 類的 apply 方法
     * 將 AlertParams 參數設定到 AlertController 中
     */ 

    public static class AlertParams {

        // 將 User 設定在 AlertParams 的設定，賦予給 AlertController
        public void apply(AlertController dialog) {
            if (mCustomTitleView != null) {
                dialog.setCustomTitle(mCustomTitleView);
            } else {
                if (mTitle != null) {
                    dialog.setTitle(mTitle);
                }
                if (mIcon != null) {
                    dialog.setIcon(mIcon);
                }
                if (mIconId != 0) {
                    dialog.setIcon(mIconId);
                }
                if (mIconAttrId != 0) {
                    dialog.setIcon(dialog.getIconAttributeResId(mIconAttrId));
                }
            }
            if (mMessage != null) {
                dialog.setMessage(mMessage);
            }
            if (mPositiveButtonText != null) {
                dialog.setButton(DialogInterface.BUTTON_POSITIVE, mPositiveButtonText,
                        mPositiveButtonListener, null);
            }
            if (mNegativeButtonText != null) {
                dialog.setButton(DialogInterface.BUTTON_NEGATIVE, mNegativeButtonText,
                        mNegativeButtonListener, null);
            }
            if (mNeutralButtonText != null) {
                dialog.setButton(DialogInterface.BUTTON_NEUTRAL, mNeutralButtonText,
                        mNeutralButtonListener, null);
            }
            if (mForceInverseBackground) {
                dialog.setInverseBackgroundForced(true);
            }
            
            // 如果有 items 代表是一個列表 View
            if ((mItems != null) || (mCursor != null) || (mAdapter != null)) {
                createListView(dialog);
            }
            if (mView != null) {
                if (mViewSpacingSpecified) {
                    dialog.setView(mView, mViewSpacingLeft, mViewSpacingTop, mViewSpacingRight,
                            mViewSpacingBottom);
                } else {
                    dialog.setView(mView);
                }
            } else if (mViewLayoutResId != 0) {
                dialog.setView(mViewLayoutResId);
            }

        }
    }
}

// Dialog.java

void dispatchOnCreate(Bundle savedInstanceState) {
    if (!mCreated) {
        onCreate(savedInstanceState);
        mCreated = true;
    }
}

protected void onCreate(Bundle savedInstanceState) {
}

// --------------------------------------------------------------
// AlertDialog.java

public class AlertDialog extends Dialog implements DialogInterface {

    private AlertController mAlert;

    void dispatchOnCreate(Bundle savedInstanceState) {
        if (!mCreated) {
            onCreate(savedInstanceState);
            mCreated = true;
        }
    }

    // 需要時可以覆寫 Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // @ 追蹤 installContent 方法
        mAlert.installContent();
    }
}

● 這其實類似一種模板模式，加載 xml 行為由子類負責

以 AlertDialog 來說就是透過 onCreate 方法，呼叫 AlertContoller 中的 PhoneWindow 加載 xml 布局

// Dialog.java

    protected void onStart() {
        if (mActionBar != null) mActionBar.setShowHideAnimationEnabled(true);
    }

private void sendShowMessage() {
        if (mShowMessage != null) {
            // Obtain a new message so this dialog can be re-used
            Message.obtain(mShowMessage).sendToTarget();
        }
    }

// AlertDialog.java

    protected final Window mWindow;    // 目前是 PhoneWindow

    private int mAlertDialogLayout;


    protected AlertController(Context context, DialogInterface di, Window window) {

        // 預設布局
        mAlertDialogLayout = a.getResourceId(
            R.styleable.AlertDialog_layout, R.layout.alert_dialog);

        ... 省略部份
    }

    public void installContent() {
        int contentView = selectContentView();

        // 加載 xml id
        mWindow.setContentView(contentView);

        // 初始化 AlertDialog 內容
        // @ 追蹤 setupView
        setupView();
    }

    // 選擇 layout view
    // 預設 xml 為 R.layout.alert_dialog
    private int selectContentView() {
        if (mButtonPanelSideLayout == 0) {
            return mAlertDialogLayout;
        }
        if (mButtonPanelLayoutHint == AlertDialog.LAYOUT_HINT_SIDE) {
            return mButtonPanelSideLayout;
        }
        // TODO: use layout hint side for long messages/lists
        return mAlertDialogLayout;
    }

● PhoneWindow#setContentView 布局加載分析：請參考 LayoutInflate 加載 Xml

// AlertDialog.java

    // 設定 R.layout.alert_dialog 布局
    private void setupView() {
        final View parentPanel = mWindow.findViewById(R.id.parentPanel);
        // 預設 3 個區塊
        final View defaultTopPanel = parentPanel.findViewById(R.id.topPanel);
        final View defaultContentPanel = parentPanel.findViewById(R.id.contentPanel);
        final View defaultButtonPanel = parentPanel.findViewById(R.id.buttonPanel);

        // Install custom content before setting up the title or buttons so
        // that we can handle panel overrides.
        final ViewGroup customPanel = (ViewGroup) parentPanel.findViewById(R.id.customPanel);
        // 設定自定義 View
        setupCustomContent(customPanel);

        // 3 個區塊的 View
        final View customTopPanel = customPanel.findViewById(R.id.topPanel);
        final View customContentPanel = customPanel.findViewById(R.id.contentPanel);
        final View customButtonPanel = customPanel.findViewById(R.id.buttonPanel);

        // Resolve the correct panels and remove the defaults, if needed.
        // 自定義 View 取代 default View
        final ViewGroup topPanel = resolvePanel(customTopPanel, defaultTopPanel);
        final ViewGroup contentPanel = resolvePanel(customContentPanel, defaultContentPanel);
        final ViewGroup buttonPanel = resolvePanel(customButtonPanel, defaultButtonPanel);

        setupContent(contentPanel);
        setupButtons(buttonPanel);
        setupTitle(topPanel);

        ... 省略部份

        // 設定 ListView
        final ListView listView = mListView;
        if (listView != null && mAdapter != null) {
            listView.setAdapter(mAdapter);
            final int checkedItem = mCheckedItem;
            if (checkedItem > -1) {
                listView.setItemChecked(checkedItem, true);
                listView.setSelection(checkedItem);
            }
        }
    }

R.layout.alert_dialog 布局概念圖