前言

最近在研究设计模式中的建造者模式，而AlertDialog源码正是采用这种模式进行设计的，故将整个AlertDialog源码都给分析了一遍。

总体框架

在MainActivity中实例化一个AlertDialog对象：

public class MainActivity extends AppCompatActivity {

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

new AlertDialog.Builder(this)

.setTitle("标题")

.setMessage("内容")

.show();

}

}

源码分析，整个时序图如下：

1.png

源码分析

1.首先我们在MainActivity中实例化一个AlertDialog.Builder对象，构造方法如下：

public Builder(Context context, int themeResId) {

P = new AlertController.AlertParams(new ContextThemeWrapper(

context, resolveDialogTheme(context, themeResId)));

}

在这个构造方法中会实例化AlertController.AlertParams对象，其实这个AlertParams就是我们传递的某些设置，诸如title、message等。

如果没做任何处理，Android Studio乃至其它的IDE是无法查看Android隐藏的源码的，而AlertController属于隐藏的源码，我们该怎么处理呢？可以查看我的另外一个博客：Android Studio 查看Android内部隐藏源码

2.然后我们调用show方法，show方法内部如下：

public AlertDialog show() {

final AlertDialog dialog = create();

dialog.show();

return dialog;

}

调用AlertDialog内部类Builder中的create方法，我们可以看看create方法内部做了哪些处理：

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;

}

创建了AlertDialog对象，并调用AlertParams对象的apply方法，接着就是给AlertDialog设置一些监听器。我们来仔细看看这个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));

}

}

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);

}

*/

}

其实这里也没什么，无非就是将我们通过链式调用设置的一些重新设置到AlertController中。

3.接下来我们返回到Builder类的show方法：

public AlertDialog show() {

final AlertDialog dialog = create();

dialog.show();

return dialog;

}

我们已经查看了create方法，再来看dialog.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) {

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方法，可以看到调用了dispatchOnCreate方法，点击进去：

void dispatchOnCreate(Bundle savedInstanceState) {

if (!mCreated) {

onCreate(savedInstanceState);

mCreated = true;

}

}

调用了onCreate方法，点击进去，Dialog类没有任何实现，这时候我们想到它的子类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方法，点击进去：

public void installContent() {

int contentView = selectContentView();

mWindow.setContentView(contentView);

setupView();

}

可以看到这里调用了setupView方法，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，如果拿房子举例来说，这个AlertController类才是房子，而AlertDialog这个类是建造者Builder，只不过它将Builder又封装了一层而已。

这里我们看到了熟悉的findViewById，那么有人又会想，那布局到底是哪一个呢？其实是alert_dialog，我们可以在AlertController这个类中搜索alert_dialog即可。

总结

细细查看一些Android源码，其实也没那么难，关键在于事在人为，但是对于一些为何要这样设计，这样设计有什么好处，这个就需要我们花时间去深思其中的奥秘！

喜欢本篇博客的简友们，就请来一波点赞，您的每一次关注，将成为我前进的动力，谢谢！