通过AlertDialog学习Builder模式

建造者模式

创建性模式。简化复杂对象的创建过程，将对象的创造和内部实现解耦，分离部件和组装过程，使得构建过程和部件可自由扩展。

AlertDialog简单使用

AlertDialog.Builder(this)
            .setTitle("title")//返回builder对象
            .setMessage("message")//返回builder对象
            .setOnCancelListener {  }
            .setPositiveButton("Positive"){dialogInterface,which ->
                dialogInterface.dismiss()}
            .setNegativeButton("Negative"){dialogInterface,_ ->
                dialogInterface.dismiss()}//返回builder对象
            .show()//构建AlertDialog并显示

---

AlterDialog解析

AlterDialog.png
AlertController.png

---

1. AlertDialog.Builder(this)

public static class Builder{ 

    private final AlertParams P;//存储构建过程中传入的参数（title、点击事件等）
    private final int mTheme;

    public Builder(@NonNull Context context) {
        this(context, AlertDialog.resolveDialogTheme(context, 0));
    }

    public Builder(@NonNull Context context, @StyleRes int themeResId) {
        this.P = new AlertParams(new ContextThemeWrapper(context, AlertDialog.resolveDialogTheme(context, themeResId)));
        this.mTheme = themeResId;
    }
    ...
    public AlertDialog.Builder setTitle(@Nullable CharSequence title) {
        this.P.mTitle = title;
        return this;
    }
    ...
    public AlertDialog.Builder setOnCancelListener(OnCancelListener onCancelListener) {
        this.P.mOnCancelListener = onCancelListener;
        return this;
    }
    ...
}

在Builder没有调用create之前：
所有的赋值操作(Builder.setXxx())都会返回Builder本身，这也使得Builder可以链式调用
Builder.setXxx()中将传入参数存储在AlertParams中，在之后创建AlertDialog时给mAlert赋值

---

2. AlertDialog.Builder.create()

AlertDialog.class
      protected AlertDialog(@NonNull Context context, @StyleRes int themeResId) {
        super(context, resolveDialogTheme(context, themeResId));
        this.mAlert = new AlertController(this.getContext(), this, this.getWindow());
      }
      public AlertDialog create() {
        AlertDialog dialog = new AlertDialog(this.P.mContext, this.mTheme);
        this.P.apply(dialog.mAlert);//将mAlert传入AlertParams，将之前AlertParams中存储的参数赋值给mAlert
        dialog.setCancelable(this.P.mCancelable);
        if (this.P.mCancelable) {
            dialog.setCanceledOnTouchOutside(true);
        }

        dialog.setOnCancelListener(this.P.mOnCancelListener);
        dialog.setOnDismissListener(this.P.mOnDismissListener);
        if (this.P.mOnKeyListener != null) {
            dialog.setOnKeyListener(this.P.mOnKeyListener);
        }

        return dialog;
    }

    public AlertDialog show() {
        AlertDialog dialog = this.create();
        dialog.show();
        return dialog;
    }


AlertController.class
    public static class AlertParams {
    ...
    public void apply(AlertController dialog) {
        if (this.mCustomTitleView != null) {
            dialog.setCustomTitle(this.mCustomTitleView);
        } else {
            if (this.mTitle != null) {
                dialog.setTitle(this.mTitle);
            }

            if (this.mIcon != null) {
                dialog.setIcon(this.mIcon);
            }

            if (this.mIconId != 0) {
                dialog.setIcon(this.mIconId);
            }

            if (this.mIconAttrId != 0) {
                dialog.setIcon(dialog.getIconAttributeResId(this.mIconAttrId));
            }
        }

        if (this.mMessage != null) {
            dialog.setMessage(this.mMessage);
        }

        if (this.mPositiveButtonText != null || this.mPositiveButtonIcon != null) {
            dialog.setButton(-1, this.mPositiveButtonText, this.mPositiveButtonListener, (Message)null, this.mPositiveButtonIcon);
        }

        if (this.mNegativeButtonText != null || this.mNegativeButtonIcon != null) {
            dialog.setButton(-2, this.mNegativeButtonText, this.mNegativeButtonListener, (Message)null, this.mNegativeButtonIcon);
        }

        if (this.mNeutralButtonText != null || this.mNeutralButtonIcon != null) {
            dialog.setButton(-3, this.mNeutralButtonText, this.mNeutralButtonListener, (Message)null, this.mNeutralButtonIcon);
        }

        if (this.mItems != null || this.mCursor != null || this.mAdapter != null) {
            this.createListView(dialog);
        }

        if (this.mView != null) {
            if (this.mViewSpacingSpecified) {
                dialog.setView(this.mView, this.mViewSpacingLeft, this.mViewSpacingTop, this.mViewSpacingRight, this.mViewSpacingBottom);
            } else {
                dialog.setView(this.mView);
            }
        } else if (this.mViewLayoutResId != 0) {
            dialog.setView(this.mViewLayoutResId);
        }

    }

AlertParams中保存创建过程中的参数
AlertController中通过AlertParams的参数给AlertDialog设置值和点击事件等

---