注意的问题

1. match_parent 表示让当前控件的大小和父布局的大小一样,也就是由父布局来决定当前控件的大小。
2. wrap_content 表示让当前控件的大小能够刚好包含住里面的内容,也就是由控件内容决定当前控件的大小。
3. 如果 LinearLayout 的排列方向是 horizontal,内部的控件就绝对不能将宽度指定为 match_parent,因为这样的话单独一个控件就会将整个水平方向占满,其他的控件就没有可放置的位置了。同样的道理,如果 LinearLayout 的排列方向是 vertical,内部的控
   件就不能将高度指定为 match_parent。

4. 我们所用的所有控件都是直接或间接继承自 View 的,所用的所有布局都是直接或间接继承自 ViewGroup 的。View 是 Android 中一种最基本的 UI 组件,它可以在屏幕上绘制一块矩形区域,并能响应这块区域的各种事件。

   
   
   snapshot1.png
5. 隐藏系统自带的标题栏

requestWindowFeature(Window.FEATURE_NO_TITLE);

最常用和最难用的控件-ListView（主要关键点是子项布局和适配器）。

*Fruit类

public class Fruit {
  private String name;
  private int imageId;
  public Fruit(String name, int imageId) {
  this.name = name;
  this.imageId = imageId;
}
public String getName() {
  return name;
}
public int getImageId() {
  return imageId;
}
}

*fruit_item.xml子项布局

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<ImageView
android:id="@+id/fruit_image"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<TextView
android:id="@+id/fruit_name"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginLeft="10dip" />
</LinearLayout>

*适配器类 FruitAdapter

public class FruitAdapter extends ArrayAdapter<Fruit> {
private int resourceId;
public FruitAdapter(Context context, int textViewResourceId,
List<Fruit> objects) {
super(context, textViewResourceId, objects);
resourceId = textViewResourceId;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
Fruit fruit = getItem(position); // 获取当前项的Fruit实例
View view = LayoutInflater.from(getContext()).inflate(resourceId, null);
ImageView fruitImage = (ImageView) view.findViewById(R.id.fruit_image);
TextView fruitName = (TextView) view.findViewById(R.id.fruit_name);
fruitImage.setImageResource(fruit.getImageId());
fruitName.setText(fruit.getName());
return view;
}
}

*MainActivity类

public class MainActivity extends Activity {
private List<Fruit> fruitList = new ArrayList<Fruit>();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initFruits(); // 初始化水果数据
FruitAdapter adapter = new FruitAdapter(MainActivity.this,
R.layout.fruit_item, fruitList);
ListView listView = (ListView) findViewById(R.id.list_view);
istView.setAdapter(adapter);
}
private void initFruits() {
Fruit apple = new Fruit("Apple", R.drawable.apple_pic);
fruitList.add(apple);
Fruit banana = new Fruit("Banana", R.drawable.banana_pic);
fruitList.add(banana);
Fruit orange = new Fruit("Orange", R.drawable.orange_pic);
fruitList.add(orange);
Fruit watermelon = new Fruit("Watermelon", R.drawable.watermelon_pic);
fruitList.add(watermelon);
Fruit pear = new Fruit("Pear", R.drawable.pear_pic);
fruitList.add(pear);
Fruit grape = new Fruit("Grape", R.drawable.grape_pic);
fruitList.add(grape);
Fruit pineapple = new Fruit("Pineapple", R.drawable.pineapple_pic);
fruitList.add(pineapple);
Fruit strawberry = new Fruit("Strawberry", R.drawable.strawberry_pic);
fruitList.add(strawberry);
Fruit cherry = new Fruit("Cherry", R.drawable.cherry_pic);
fruitList.add(cherry);
Fruit mango = new Fruit("Mango", R.drawable.mango_pic);
fruitList.add(mango);
}
}

提升 ListView 的运行效率