概念
建造者模式是较为简单的创立型模式，将组件和组件的组件过程离开，而后一步一步建造一个简单的对象。所以建造者模式又叫生成器模式。它容许用户在不晓得外部构建细节的状况下，十分精密地管制对象构建流程。该模式是为了将构建过程非常复杂的对象进行拆分，让它与它的部件解耦，晋升代码的可读性以及扩展性。
应用场景：
结构一个对象须要很多参数的时候，并且参数的个数或者类型不固定的时候
UML 结构图
例：
// 创立简单对象 Product
public class Product {
private String partA;
private String partB;
private String partC;
public String getPartA() {return partA;}
public void setPartA(String partA) {this.partA = partA;}
public String getPartB() {return partB;}
public void setPartB(String partB) {this.partB = partB;}
public String getPartC() {return partC;}
public void setPartC(String partC) {this.partC = partC;}
}
// 创立抽象类 Builder
public abstract class Builder {protected Product product = new Product();
public abstract void builderPartA();
public abstract void builderPartB();
public abstract void builderPartC();
public Product getResult() {return product;}
}
// 创立实现类 ConcreateBuilder
public class ConcreateBuilder extends Builder {
@Override
public void builderPartA() {}
@Override
public void builderPartB() {}
@Override
public void builderPartC() {}
}
// 创立组装对象 Director
public class Director {
private Builder builder;
public Director(Builder builder){this.builder = builder;}
public void setBuilder(Builder builder) {this.builder = builder;}
public Product constract(){builder.builderPartA();
builder.builderPartB();
builder.builderPartC();
return builder.getResult();}
}// 运行
Builder builder = new ConcreateBuilder();
Director director = new Director(builder);
Product product = director.constract();Builder：他为创立一个创立 Product 对象的各个部件指定形象接口
ConcreateBuilder：它实现了 builder 接口，实现各个部件的具体结构和拆卸办法。
Product：他是被构建的简单对象，包好多个组成部件。
Director：指挥者又称为导演类，负责安顿简单对象的建造秩序，指挥者与形象建造者之间存在关联关系。
长处：
涣散耦合：生成其模式能够用同一个结构算法构建出体现上齐全不同的产品，实现产品构建和产品体现上的拆散。
很容易扭转产品外部示意。
更好的复用性：生成器模式很好的实现了构建算法和具体产品实现的拆散。
毛病：
会产生多余的 Builder 对象，Director 对象，耗费内存。
对象构建过程裸露。
android SDK 源码剖析
先看应用
// 实例化一个 AlertDialog 对象：new AlertDialog.Builder(this)
.setTitle("题目")
.setMessage("内容")
.show();AlertDialog.Builder 构造方法如下
public Builder(Context context, int themeResId) {
P = new AlertController.AlertParams(new ContextThemeWrapper(context, resolveDialogTheme(context, themeResId)));
}AlertParams 就是咱们理论传递的设置
// 而后调用 show 办法
public AlertDialog show() {final AlertDialog dialog = create();
dialog.show();
return dialog;
}
//create
public AlertDialog create() {
// Context has already been wrapped with the appropriate theme.
final AlertDialog dialog = new AlertDialog(P.mContext, 0, false);
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;
}
//apply
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);
}
// For a list, the client can either supply an array of items or an
// adapter or a cursor
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.setCancelable(mCancelable);
dialog.setOnCancelListener(mOnCancelListener);
if (mOnKeyListener != null) {dialog.setOnKeyListener(mOnKeyListener);
}
*/
}
//dialog 的 show 办法
public void show() {if (mShowing) {if (mDecor != null) {if (mWindow.hasFeature(Window.FEATURE_ACTION_BAR)) {mWindow.invalidatePanelMenu(Window.FEATURE_ACTION_BAR);
}
mDecor.setVisibility(View.VISIBLE);
}
return;
}
mCanceled = false;
if (!mCreated) {dispatchOnCreate(null);
} else {
// Fill the DecorView in on any configuration changes that
// may have occured while it was removed from the WindowManager.
final Configuration config = mContext.getResources().getConfiguration();
mWindow.getDecorView().dispatchConfigurationChanged(config);
}
onStart();
mDecor = mWindow.getDecorView();
if (mActionBar == null && mWindow.hasFeature(Window.FEATURE_ACTION_BAR)) {final ApplicationInfo info = mContext.getApplicationInfo();
mWindow.setDefaultIcon(info.icon);
mWindow.setDefaultLogo(info.logo);
mActionBar = new WindowDecorActionBar(this);
}
WindowManager.LayoutParams l = mWindow.getAttributes();
if ((l.softInputMode
& WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION) == 0) {WindowManager.LayoutParams nl = new WindowManager.LayoutParams();
nl.copyFrom(l);
nl.softInputMode |=
WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION;
l = nl;
}
mWindowManager.addView(mDecor, l);
mShowing = true;
sendShowMessage();}其实这里是调用父类 Dialog 的 show 办法，能够看到调用了 dispatchOnCreate 办法，点击进去：
void dispatchOnCreate(Bundle savedInstanceState) {if (!mCreated) {onCreate(savedInstanceState);
mCreated = true;
}
}调用了 onCreate 办法，点击进去，Dialog 类没有任何实现，这时候咱们想到它的子类 AlertDialog，去这个类找 onCreate 的实现：
protected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);
mAlert.installContent();}调用了 AlertController 对象的 installContent 办法，点击进去：
public void installContent() {
int contentView = selectContentView();
mWindow.setContentView(contentView);
setupView();}能够看到这里调用了 setupView 办法，点击进去：
private void setupView() {final View parentPanel = mWindow.findViewById(R.id.parentPanel);
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);
setupCustomContent(customPanel);
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.
final ViewGroup topPanel = resolvePanel(customTopPanel, defaultTopPanel);
final ViewGroup contentPanel = resolvePanel(customContentPanel, defaultContentPanel);
final ViewGroup buttonPanel = resolvePanel(customButtonPanel, defaultButtonPanel);
setupContent(contentPanel);
setupButtons(buttonPanel);
setupTitle(topPanel);
}原来真正的布局与设置都是在这里
而你仅仅只设置了 message 和 title，其余的你一概不知