Deep understanding of the builder model in Android _android

Objective

During the Android development, I found that many An Zhouyuan code used design patterns, more commonly used adapter patterns (various adapter), Builder Mode (Alert dialog build), and so on. Although we know a lot about design patterns, in this aspect of applying design patterns, it feels like many people are lacking in this. So this article is a deep understanding of the builder model in Android.

Builder mode (Builder pattern) is also called the generator pattern, which is defined as follows:

Separate the construction of a complex object from it representation so this same construction process can create dif Ferent representations. Separates the build of a complex object from its markup, so that the same build process can create different representations.

My understanding: To separate a product (object) representation from the build process so that the product is built in the same way that it can have different product representations.

Application Scenarios

Here's a common example of Android:

The construction of the Alertdialog dialog box in Android is a typical application of the builder model.

Take a look at builder source

 public static class Builder {private final alertcontroller.alertparams P;
  Public Builder {This (context, resolvedialogtheme (context, 0));
        {P = new Alertcontroller.alertparams (Builder, int themeresid) (New Contextthemewrapper (
  Context, Resolvedialogtheme (context, themeresid)); }//Various set parameter Methods Settitle () .../** * Creates an {@link Alertdialog} with the arguments supplied to
   This * builder. * <p> * Calling this method does not display the dialog. If no additional * processing is needed, {@link #show ()} May was called instead to both * Create and display the dial
   og.
    * * 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;  //This show method is a builder object, which encapsulates create () and show () to directly Fetch and Display dialog box public Alertdialog shows () {Final Alertdialog Dialog
    = Create ();
    Dialog.show ();
  return dialog; }
}

Analysis of the source can see the inner class Builder is used to build this dialog box:

1, builder when created, will put this AlertController.AlertParams P; object p create new out

2, in the bilder setting of various parameters, these parameters exist in the object P

3, then builder the parameter is set up after the call create method.

Final Alertdialog Dialog = new Alertdialog (P.mcontext, 0, false);
P.apply (Dialog.malert); Malert is in the outer class

In this method, the constructor of the outer class is called First AlertDialog , new an external class object is created, and then the p.apply() method assigns the object p as the property of the inner class AlertController mAlert . This completes a build.

The following is part of the source code of Alertdialog

public class Alertdialog extends Dialog implements Dialoginterface {
  //This object is used to accept parameters set within the builder
  private Alertcontroller Malert;

  The following construction methods determine that only the inner class builder can be used to construct
  the protected alertdialog (context
    , 0);

  Protected Alertdialog (Context, Boolean cancelable,   Oncancellistener cancellistener) {This
    (context, 0 );
    Setcancelable (cancelable);
    Setoncancellistener (Cancellistener);
  }


  Protected Alertdialog (context, @StyleRes int themeresid) {This
    (context, themeresid, true);
  }

  Alertdialog (context, @StyleRes int Themeresid, Boolean createcontextthemewrapper) {
    Super (context, Createcontextthemewrapper? Resolvedialogtheme (Context, Themeresid): 0,
      createcontextthemewrapper);

    Mwindow.alwaysreadcloseontouchattr ();
    Malert = new Alertcontroller (GetContext (), this, GetWindow ());
    }

Summarize

The above is the full content of this article, I hope this article on the content of Android developers can help, if you have questions you can message exchange.