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