Android源码分析之Builder模式

// AlertDialog

public class AlertDialog extends Dialog implements DialogInterface {

    // Controller, 接受Builder成员变量P中的各个参数

    private AlertController mAlert;

    // 构造函数

    protected AlertDialog(Context context, int theme) {

        this(context, theme, true);

    }

    // 4 : 构造AlertDialog

    AlertDialog(Context context, int theme, boolean createContextWrapper) {

        super(context, resolveDialogTheme(context, theme), createContextWrapper);

        mWindow.alwaysReadCloseOnTouchAttr();

        mAlert = new AlertController(getContext(), this, getWindow());

    }

    // 实际上调用的是mAlert的setTitle方法

    @Override

    public void setTitle(CharSequence title) {

        super.setTitle(title);

        mAlert.setTitle(title);

    }

    // 实际上调用的是mAlert的setCustomTitle方法

    public void setCustomTitle(View customTitleView) {

        mAlert.setCustomTitle(customTitleView);

    }

     

    public void setMessage(CharSequence message) {

        mAlert.setMessage(message);

    }

    // AlertDialog其他的代码省略

     

    // ************  Builder为AlertDialog的内部类   *******************

    public static class Builder {

        // 1 : 存储AlertDialog的各个参数, 例如title, message, icon等.

        private final AlertController.AlertParams P;

        // 属性省略

         

        /**

         * Constructor using a context for this builder and the {@link AlertDialog} it creates.

         */

        public Builder(Context context) {

            this(context, resolveDialogTheme(context, 0));

        }

        public Builder(Context context, int theme) {

            P = new AlertController.AlertParams(new ContextThemeWrapper(

                    context, resolveDialogTheme(context, theme)));

            mTheme = theme;

        }

         

        // Builder的其他代码省略 ......

        // 2 : 设置各种参数

        public Builder setTitle(CharSequence title) {

            P.mTitle = title;

            return this;

        }

         

         

        public Builder setMessage(CharSequence message) {

            P.mMessage = message;

            return this;

        }

        public Builder setIcon(int iconId) {

            P.mIconId = iconId;

            return this;

        }

         

        public Builder setPositiveButton(CharSequence text, final OnClickListener listener) {

            P.mPositiveButtonText = text;

            P.mPositiveButtonListener = listener;

            return this;

        }

         

         

        public Builder setView(View view) {

            P.mView = view;

            P.mViewSpacingSpecified = false;

            return this;

        }

         

        // 3 : 构建AlertDialog, 传递参数

        public AlertDialog create() {

            // 调用new AlertDialog构造对象， 并且将参数传递个体AlertDialog

            final AlertDialog dialog = new AlertDialog(P.mContext, mTheme, false);

            // 5 : 将P中的参数应用的dialog中的mAlert对象中

            P.apply(dialog.mAlert);

            dialog.setCancelable(P.mCancelable);

            if (P.mCancelable) {

                dialog.setCanceledOnTouchOutside(true);

            }

            dialog.setOnCancelListener(P.mOnCancelListener);

            if (P.mOnKeyListener != null) {

                dialog.setOnKeyListener(P.mOnKeyListener);

            }

            return dialog;

        }

    }

     

}