1.单位dp、dip、sp、pt、px、in、mm
这里引用StackOverFlow上的一个解答：
Here is the difference
dpDensity-independent Pixels - an abstract unit that is based on the physical density of the screen. These units are relative to a 160 dpi screen, so one dp is one pixel on a 160 dpi screen. The ratio of dp-to-pixel will change with the screen density, but not necessarily in direct PRoportion. Note: The compiler accepts both "dip" and "dp", though "dp" is more consistent with "sp".即：dp=160*px/dpispScale-independent Pixels - this is like the dp unit, but it is also scaled by the user's font size preference. It is recommend you use this unit when specifying font sizes, so they will be adjusted for both the screen density and user's preference.Remenber this：You would use
spfor font sizesdipfor everything elseandroid:id="@+id/input_message"android:layout_width="0dp"android:layout_height="wrap_content"android:layout_weight="1"android:hint="Type something"/><Button
android:id="@+id/send"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="Send"/>5.一个简易快速ListView，可显示一批Stringprivate String[] data = { "Apple", "Banana", "Orange", "Watermelon","Pear", "Grape", "Pineapple", "Strawberry", "Cherry", "Mango" };@Overrideprotected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);ArrayAdapter<String> adapter = new ArrayAdapter<String>(MainActivity.this, android.R.layout.simple_list_item_1, data);ListView listView = (ListView) findViewById(R.id.list_view);listView.setAdapter(adapter);}6.自定义Adapter时候重载getView（）方法的作用这个方法在每个子项被滚动到屏幕内的时候会被调用7.ListView性能优化使用Adapter中getView()方法的参数convertView，避免每次重复加载布局文件使用ViewHolder来记录绑定的控件id与控件实例8.编写聊天界面方式选择使用一个布局，用于存储来往消息气泡，根据消息流向设置控件可见性这样的方式要优于使用多个布局文件
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