Android小知識-理解設計模式中的建造者模式

摘要： 建造者模式的定義是：將一個複雜物件的構建與它的表示分離，使得同樣的構建過程可以建立不同的表示。也就是說將構建過程和部件的表示隔離開，使用者可以在不知道內部構建細節的情況下，對物件的構造流程進行相應的控制，比如在Android中典型的Builder模式就是AlerDialog.Builder類。...

建造者模式的定義是：將一個複雜物件的構建與它的表示分離，使得同樣的構建過程可以建立不同的表示。也就是說將構建過程和部件的表示隔離開，使用者可以在不知道內部構建細節的情況下，對物件的構造流程進行相應的控制，比如在Android中典型的Builder模式就是AlerDialog.Builder類。

先看下UML圖：

模型圖上的四個角色介紹如下：

1. builder：為建立一個產品物件的各個部件指定抽象介面。

2. ConcreteBuilder：實現Builder的介面以構造和裝配該產品的各個部件，定義並明確它所建立的表示，並 提供一個檢索產品的介面。

3. Director：構造一個使用Builder介面的物件。

4. Product：表示被構造的複雜物件。ConcreteBuilder建立該產品的內部表示並定義它的裝配過程，包含定義組成部件的類，包括將這些部件裝配成最終產品的介面。

package com.apk.administrator.loadapk;

/**
 * Product
 * 具體的產品
 */
public class Person {
private String head;
private String body;
private String foot;

public String getHead() {
return head;
}

public void setHead(String head) {
this.head = head;
}

public String getBody() {
return body;
}

public void setBody(String body) {
this.body = body;
}

public String getFoot() {
return foot;
}

public void setFoot(String foot) {
this.foot = foot;
}
}

package com.apk.administrator.loadapk;

/**
 * Builder
 * 產品構建的抽象介面
 */
public interface PersonBuilder {
void buildHead();

void buildBody();

void buildFoot();

Person buildPerson();
}

/**
 * Director
 * 建造者
 */
public class PersonDirector {
public Person constructPerson(PersonBuilder pb) {
pb.buildHead();
pb.buildBody();
pb.buildFoot();
return pb.buildPerson();
}
}

package com.apk.administrator.loadapk;

/**
 * ConcreteBuilder
 * 具體建造工具(建立一個男人)
 */
public class ManBuilder implements PersonBuilder {
Person person;

public ManBuilder() {
person = new Person();
}

public void buildBody() {
person.setBody("建造男人的身體");
}

public void buildFoot() {
person.setFoot("建造男人的腳");
}

public void buildHead() {
person.setHead("建造男人的頭");
}

public Person buildPerson() {
return person;
}
}

package com.apk.administrator.loadapk;

public class Test {
public static void main(String[] args) {
PersonDirector pd = new PersonDirector();
Person person = pd.constructPerson(new ManBuilder());
System.out.println(person.getBody());
System.out.println(person.getFoot());
System.out.println(person.getHead());
}
}

上面程式碼中最終的目的是要建立一個男人的物件，具體怎麼建立使用者不關心，只需要通過建造者PersonDirector建立一個物件，什麼物件？ManBuilder物件，這樣男人物件就創建出來了。

案例：Dialog的封裝

在封裝Dialog時，會使用靜態內部類Builder對Diloag的標題、內容、按鈕以及事件監聽進行配置，並通過CommonDialog類展示。

可以看出這是很典型的Builder模式，在配置引數時返回的是Builder本身，這樣的話可以通過鏈式呼叫，使程式碼的可讀性大大提高。由於封裝的是Dialog，因此，Builder類會去繼承Dialog來自定義Dialog。下面貼出完整的Dialog封裝類：

package com.glh.getproject.view;

import android.app.Dialog;
import android.content.Context;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.Gravity;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.WindowManager;
import android.widget.TextView;

import com.glh.getproject.R;


public class CommonDialog {

private Builder mBuilder;

private CommonDialog(Builder builder) {
this.mBuilder = builder;
}

public void show() {
mBuilder.showDialog();
}

public static class Builder extends Dialog implements OnClickListener {

private TextView tv_title;
private TextView tv_left;
private TextView tv_right;
private TextView tv_info;

private DialogListener mDialogListener;

private String title;
private String info;
private String strLeftBtn;
private String strRightBtn;

public interface DialogListener {
void ok();

void cancel();
}

void showDialog() {
show();
}

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.dialogl_info_show);
initUI();
initEvent();
initViewStatus();
}

private void initUI() {
tv_title = findViewById(R.id.tv_title);
tv_left = findViewById(R.id.tv_left);
tv_right = findViewById(R.id.tv_right);
tv_info = findViewById(R.id.tv_info);
}

private void initViewStatus() {
if (!TextUtils.isEmpty(title)) {
tv_title.setText(title);
}
if (!TextUtils.isEmpty(info)) {
tv_info.setText(info);
}
if (!TextUtils.isEmpty(strLeftBtn)) {
tv_left.setText(strLeftBtn);
} else {
tv_left.setText("確定");
}
if (!TextUtils.isEmpty(strRightBtn)) {
tv_right.setText(strRightBtn);
} else {
tv_right.setText("取消");
}
}

private void initEvent() {
tv_left.setOnClickListener(this);
tv_right.setOnClickListener(this);
}

@Override
public void onClick(View v) {

switch (v.getId()) {
case R.id.tv_left:
if (mDialogListener != null) {
dismiss();
mDialogListener.ok();
}
break;
case R.id.tv_right:
if (mDialogListener != null) {
dismiss();
mDialogListener.cancel();
}
break;
default:
break;
}

}

public Builder(Context context) {
super(context, R.style.MessageBox);
setCanceledOnTouchOutside(false);
getWindow().setBackgroundDrawableResource(android.R.color.transparent);
WindowManager.LayoutParams wl = getWindow().getAttributes();
wl.gravity = Gravity.CENTER;
getWindow().setAttributes(wl);
}

public Builder setListener(DialogListener listener) {
this.mDialogListener = listener;
return this;
}

public Builder setTitle(String title) {
this.title = title;
return this;
}

public Builder setInfo(String info) {
this.info = info;
return this;
}

public Builder setLeftButtonTitle(String title) {
this.strLeftBtn = title;
return this;
}

public Builder setRightButtonTitle(String title) {
this.strRightBtn = title;
return this;
}

public CommonDialog build() {
return new CommonDialog(this);
}
}


}

相關的Style：

<style name="MessageBox">
<item name="android:windowNoTitle">true</item>
<item name="android:windowIsFloating">true</item>
<item name="android:windowContentOverlay">@null</item>
<item name="android:layout_gravity">center</item>
</style>

layout檔案：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="@android:color/transparent">


<RelativeLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:layout_marginLeft="20dp"
android:layout_marginRight="20dp"
android:background="@drawable/dialog_background_shape"
android:paddingLeft="16dp"
android:paddingRight="16dp">

<LinearLayout
android:id="@+id/ll_title"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_marginTop="20dp"
android:gravity="center_horizontal"
android:orientation="vertical">

<TextView
android:id="@+id/tv_title"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:gravity="center"
android:lineSpacingExtra="2dp"
android:textColor="@color/title"
android:textSize="17sp"
android:visibility="visible" />

<TextView
android:id="@+id/tv_info"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:gravity="center"
android:lineSpacingExtra="2dp"
android:paddingTop="20dp"
android:textColor="@color/title"
android:textSize="17sp"
android:visibility="visible" />

</LinearLayout>


<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_below="@id/ll_title"
android:layout_centerHorizontal="true"
android:layout_marginTop="25dp"
android:gravity="center"
android:orientation="horizontal"
android:paddingBottom="20dp"
android:visibility="visible">

<TextView
android:id="@+id/tv_left"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginRight="5dp"
android:layout_weight="1"
android:background="@drawable/red_button_shape"
android:gravity="center"
android:paddingBottom="7dp"
android:paddingLeft="30dp"
android:paddingRight="30dp"
android:paddingTop="7dp"
android:textColor="@color/white"
android:textSize="14sp"
android:visibility="visible" />

<TextView
android:id="@+id/tv_right"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginLeft="5dp"
android:layout_weight="1"
android:background="@drawable/gray_button_shape"
android:gravity="center"
android:paddingBottom="7dp"
android:paddingLeft="30dp"
android:paddingRight="30dp"
android:paddingTop="7dp"
android:textColor="@color/white"
android:textSize="14sp"
android:visibility="visible" />

</LinearLayout>


</RelativeLayout>


</RelativeLayout>

整個Dialog的佈局背景和按鈕都是通過自定義Shape來實現的。

dialog_background_shape：

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">

<solid android:color="@color/white" />

<corners android:radius="10dp" />

</shape>

red_button_shape：

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">

<corners android:radius="5dp" />

<solid android:color="#FA001F" />

</shape>

gray_button_shape：

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">

<corners android:radius="5dp" />

<solid android:color="@color/gray" />

</shape>

在Activity中使用：

public void showDialog() {
CommonDialog commonDialog = new CommonDialog.Builder(this)
.setListener(new CommonDialog.Builder.DialogListener() {
@Override
public void ok() {
Toast.makeText(MainActivity.this, "正在更新...", Toast.LENGTH_SHORT).show();
}

@Override
public void cancel() {

}
}).setTitle("更新通知")
.setInfo("當前版本暫不可用，請下載最新版本，以便享受優質內容。")
.setLeftButtonTitle("知道了")
.setRightButtonTitle("不需要")
.build();
commonDialog.show();
}

案例二：PopupWindow的封裝

package com.glh.getproject.view;

import android.content.Context;
import android.graphics.drawable.BitmapDrawable;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.PopupWindow;
import android.widget.TextView;

import com.glh.getproject.R;


/**
 * 更新彈框
 * Created by glh on 2017-05-09.
 */
public class UpdateDialog {

private PopupWindow mPopupWindow;

private Builder mBuilder;


private UpdateDialog(Builder builder) {
this.mBuilder = builder;
View mPopupLayout = builder.mPopupLayout;
this.mPopupWindow = new PopupWindow(mPopupLayout, ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT, true);
this.mPopupWindow.setContentView(mPopupLayout);
this.mPopupWindow.setOutsideTouchable(true);
this.mPopupWindow.setFocusable(true);
this.mPopupWindow.setBackgroundDrawable(new BitmapDrawable());
this.mPopupWindow.setOnDismissListener(new PopupWindow.OnDismissListener() {
@Override
public void onDismiss() {
if (mBuilder.mCloseListener != null) {
mBuilder.mCloseListener.onClose();
}
}
});
this.mPopupWindow.update();
}

public void dismiss() {
if (!mPopupWindow.isShowing()) {
return;
}
mPopupWindow.dismiss();
}

public void showAtLocation(View parent, int gravity, int x, int y) {
mPopupWindow.showAtLocation(parent, gravity, x, y);
}

public static class Builder {

private View mPopupLayout;
private TextView tv_title;
private TextView tv_left;
private TextView tv_right;
private TextView tv_info;

private UpgradeListener mUpgradeListener;
private CloseListener mCloseListener;

private void initEvent() {
tv_left.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if (mUpgradeListener != null) {
mUpgradeListener.upgrade(true);
}
}
});
tv_right.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if (mUpgradeListener != null) {
mUpgradeListener.upgrade(false);
}
}
});
}

public interface UpgradeListener {
void upgrade(boolean upgrade);
}

public interface CloseListener {
void onClose();
}

public Builder(Context context) {
mPopupLayout = LayoutInflater.from(context).inflate(R.layout.dialogl_info_show, null, true);
tv_title = mPopupLayout.findViewById(R.id.tv_title);
tv_left = mPopupLayout.findViewById(R.id.tv_left);
tv_right = mPopupLayout.findViewById(R.id.tv_right);
tv_info = mPopupLayout.findViewById(R.id.tv_info);
initEvent();
}

public Builder setUpgradeListener(UpgradeListener listener) {
this.mUpgradeListener = listener;
return this;
}

public Builder setCloseListener(CloseListener listener) {
this.mCloseListener = listener;
return this;
}

public Builder setTitle(String title) {
this.tv_title.setText(title);
return this;
}

public Builder setInfo(String info) {
this.tv_info.setText(info);
return this;
}

public Builder setLeftButtonTitle(String title) {
this.tv_left.setText(title);
return this;
}

public Builder setRightButtonTitle(String title) {
this.tv_right.setText(title);
return this;
}

public UpdateDialog build() {
return new UpdateDialog(this);
}

}

}

layout檔案和Dialog的佈局檔案一樣，這裡就不貼出來了。

在Activity的使用：

private UpdateDialog commonDialog;

private void showPopupWindow() {
if (null == commonDialog) {
commonDialog = new UpdateDialog.Builder(this)
.setUpgradeListener(new UpdateDialog.Builder.UpgradeListener() {
@Override
public void upgrade(boolean upgrade) {
commonDialog.dismiss();
if (upgrade) {
Toast.makeText(MainActivity.this, "正在更新...", Toast.LENGTH_SHORT).show();
}
}
}).setCloseListener(new UpdateDialog.Builder.CloseListener() {
@Override
public void onClose() {
Toast.makeText(MainActivity.this, "對話方塊關閉了", Toast.LENGTH_SHORT).show();
}
}).setTitle("更新通知")
.setInfo("當前版本暫不可用，請下載最新版本，以便享受優質內容。")
.setLeftButtonTitle("知道了")
.setRightButtonTitle("不需要")
.build();
}
commonDialog.showAtLocation(mGroup, Gravity.CENTER, 0, 0);
}

總結

總的來說相同的方法，不同的執行順序，產生不同的事件結果時，可以考慮採用建造者模式；多個部件或零件，都可以裝配到一個物件中，但產生的執行結果又不相同時，可以考慮採用建造者模式；產品類非常複雜，或者產品類中的呼叫順序不同產生了不同的效能，可以考慮採用建造者模式。

搜尋微信“顧林海”公眾號，定期推送優質文章。