Home | History | Annotate | Download | only in articles 
      1 page.title=UI Framework Changes in Android 1.6
      2 parent.title=Articles
      3 parent.link=../browser.html?tag=article
      4 @jd:body
      5 
      6 <p>Android 1.6 introduces numerous enhancements and bug fixes in the UI
      7 framework. This article highlights two improvements in particular: more flexible
      8 and robust RelativeLayout and easier click listeners. </p>
      9 
     10 <h3>More flexible, more robust RelativeLayout</h3>
     11 
     12 <p>RelativeLayout is the most versatile layout offered by the Android UI toolkit
     13 and can be successfully used to reduce the number of views created by your
     14 applications. This layout used to suffer from various bugs and limitations,
     15 sometimes making it difficult to use without having some knowledge of its
     16 implementation. To make your life easier, Android 1.6 comes with a revamped
     17 RelativeLayout. </p>
     18 
     19 <p>This new implementation not only fixes all known bugs in 
     20 RelativeLayout but also addresses its major limitation: the
     21 fact that views had to be declared in a particular order. Consider the following
     22 XML layout:</p>
     23 
     24 <pre>&lt;?xml version="1.0" encoding="utf-8"?&gt;
     25 
     26 &lt;RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
     27     android:layout_width="fill_parent"
     28     android:layout_height="64dip"
     29     android:padding="6dip"&gt;
     30 
     31     &lt;TextView
     32         android:id="@+id/band"  
     33         android:layout_width="fill_parent" 
     34         android:layout_height="26dip" 
     35 
     36         android:layout_below="@+id/track"
     37         android:layout_alignLeft="@id/track"
     38         android:layout_alignParentBottom="true"
     39 
     40         android:gravity="top"
     41         android:text="The Airborne Toxic Event" /&gt;
     42 
     43     &lt;TextView
     44         android:id="@id/track"  
     45         android:layout_marginLeft="6dip"
     46         android:layout_width="fill_parent"
     47         android:layout_height="26dip"
     48 
     49         android:layout_toRightOf="@+id/artwork"
     50 
     51         android:textAppearance="?android:attr/textAppearanceMedium"
     52         android:gravity="bottom"
     53         android:text="Sometime Around Midnight" /&gt;
     54         
     55     &lt;ImageView
     56         android:id="@id/artwork"
     57         android:layout_width="56dip"
     58         android:layout_height="56dip"
     59         android:layout_gravity="center_vertical"
     60 
     61         android:src="@drawable/artwork" /&gt;
     62         
     63 &lt;/RelativeLayout&gt;</pre>
     64 
     65 <p>This code builds a very simple layoutan image on the left with two lines of
     66 text stacked vertically. This XML layout is perfectly fine and contains no
     67 errors. Unfortunately, Android 1.5's RelativeLayout is incapable of rendering it
     68 correctly, as shown in the screenshot below.</p>
     69 
     70 <img src="images/ui-1.6_002.png" style="width: 320px; height: 480px;">
     71 
     72 <p>The problem is that this layout uses forward references. For instance, the
     73 "band" TextView is positioned below the "track" TextView but "track" is declared
     74 after "band" and, in Android 1.5, RelativeLayout does not know how to handle
     75 this case. Now look at the exact same layout running on Android 1.6:</p>
     76 
     77 <img src="images/ui-1.6.png" style="width: 320px; height: 480px;">
     78 
     79 <p>As you can see Android 1.6 is now better able to handle forward reference.
     80 The result on screen is exactly what you would expect when writing the
     81 layout.</p>
     82 
     83 <h3>Easier click listeners</h3>
     84 
     85 <p>Setting up a click listener on a button is very common task, but 
     86 it requires quite a bit of boilerplate code:</p>
     87 
     88 <pre>findViewById(R.id.myButton).setOnClickListener(new View.OnClickListener() {
     89     public void onClick(View v) {
     90         // Do stuff
     91     }
     92 });</pre>
     93 
     94 <p>One way to reduce the amount of boilerplate is to share a single click
     95 listener between several buttons. While this technique reduces the
     96 number of classes, it still requires a fair amount of code and it still
     97 requires giving each button an id in your XML layout file:</p>
     98 
     99 <pre>View.OnClickListener handler = View.OnClickListener() {
    100     public void onClick(View v) {
    101         switch (v.getId()) {
    102             case R.id.myButton: // doStuff
    103                 break;
    104             case R.id.myOtherButton: // doStuff
    105                 break;
    106         }
    107     }
    108 }
    109 
    110 findViewById(R.id.myButton).setOnClickListener(handler);
    111 findViewById(R.id.myOtherButton).setOnClickListener(handler);</pre>
    112 
    113 <p>With Android 1.6, none of this is necessary. All you have to do is 
    114 declare a public method in your Activity to handle the click 
    115 (the method <i>must</i> have one View argument):</p>
    116 
    117 <pre>class MyActivity extends Activity {
    118     public void myClickHandler(View target) {
    119         // Do stuff
    120     }
    121 }</pre>
    122 
    123 <p>And then reference this method from your XML layout:</p>
    124 
    125 <pre>&lt;Button android:onClick="myClickHandler" /&gt;</pre>
    126 
    127 <p>This new feature reduces both the amount of Java and XML you have to write,
    128 leaving you more time to concentrate on your application.</p>
    129 
    130 <p>The Android team is committed to helping you write applications in the
    131 easiest and most efficient way possible. We hope you find these improvements
    132 useful and we're excited to see your applications on Android Market.</p>
    133