在Android源碼中亿柑，最常用到的Builder模式的就是AlertDialog.Builder.

public class AlertDialog extends AppCompatDialog implements DialogInterface {

    final AlertController mAlert;   //用來接收Builder成員變量P中的各個(gè)參數(shù)
    static final int LAYOUT_HINT_SIDE = 1;
   protected AlertDialog(@NonNull Context context) {
        this(context, 0);
    }


    protected AlertDialog(@NonNull Context context, @StyleRes int themeResId) {
        super(context, resolveDialogTheme(context, themeResId));
        mAlert = new AlertController(getContext(), this, getWindow());
    }

......................省略代碼...................
    @Override
    public void setTitle(CharSequence title) {
        super.setTitle(title);
  //實(shí)際上是mAlert的setTitle方法
        mAlert.setTitle(title);
    }

 Builder是AlertDialog 的內(nèi)部類
public static class Builder {
        private final AlertController.AlertParams P;
        private final int mTheme;

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


//設(shè)置各種參數(shù)
        public Builder setView(View view) {
            P.mView = view;
            P.mViewLayoutResId = 0;
            P.mViewSpacingSpecified = false;
            return this;
        }
//構(gòu)建AlertDialog邢疙，傳遞參數(shù)
        public AlertDialog create() {
       
            final AlertDialog dialog = new AlertDialog(P.mContext, mTheme);
//將p中的參數(shù)應(yīng)用到dialog的mAlert對(duì)象中
            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;
        }

     }
上述代碼中，Builder設(shè)置AlertDialog中title、message疟游、button等參數(shù)呼畸，這些參數(shù)都存儲(chǔ)在AlertController.AlertParams P中，其中包含了與AlertDialog視圖中對(duì)應(yīng)的成員變量

看一下P.apply()方法
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));
                }
            } 
在apply函數(shù)中颁虐，只是將AlertParams 參數(shù)設(shè)置到AlertController中蛮原，例如，將標(biāo)題設(shè)置到Dialog對(duì)應(yīng)的標(biāo)題視圖中另绩，需要我們調(diào)用show()方法儒陨。

   show()方法
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) {
//來調(diào)用AlertDialog的oncreate()函數(shù)
            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);
        }
//調(diào)用Alert的onstart方法
        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;
        }
//將Dialog的DecorView添加到WindowManager中
        mWindowManager.addView(mDecor, l);
        mShowing = true;

        sendShowMessage();
    }

下面來看一下dispatchOnCreate（）這個(gè)方法


 void dispatchOnCreate(Bundle savedInstanceState) {
        if (!mCreated) {
            onCreate(savedInstanceState);//調(diào)用Dialog的oncreate，空方法笋籽，   AlertDialog繼承Dialog蹦漠，其自身實(shí)現(xiàn)
            mCreated = true;
        }
    }

AlertDialog的oncreate()方法
 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mAlert.installContent();
    }
跳轉(zhuǎn)進(jìn)去，查看其方法
public void installContent() {
        final int contentView = selectContentView();
        mDialog.setContentView(contentView);
        setupView();
    }
調(diào)用setContentView和Activity的一樣车海，這里設(shè)置AlertDialog的內(nèi)容布局笛园，這個(gè)內(nèi)容布局就是mAlertDialogLayout字段的值，這個(gè)值在AlertController的構(gòu)造函數(shù)中進(jìn)行了初始化侍芝。

最后就是setupView（）方法了研铆，初始化AlertDialog布局中各個(gè)部分，Dialog視圖部分設(shè)置完畢州叠。 當(dāng)用戶調(diào)用show（）方法時(shí)棵红，WindowManager會(huì)將Window的DecorView（mAlertDialogLayout的視圖）， mWindowManager.addView(mDecor, l);添加到用戶窗口上咧栗。
至此逆甜，Dialog就出現(xiàn)在用戶的視野中了。楼熄。忆绰。浩峡。可岂。

Builder模式