4.2的sdk 就没有这个判断，请问一下这个if里面getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment()).commit(); 是什么意思？有什么作用呢？
public class MainActivity extends ActionBarActivity {
private TimePicker picker;
private Button button;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.timepicker);
picker = (TimePicker)findViewById(R.id.firstTimePicker);
button = (Button)findViewById(R.id.button);
//该函数用于设置是否使用24小时制显示时间
picker.setIs24HourView(true);
TimeListener timeListener = new TimeListener();
picker.setOnTimeChangedListener(timeListener);
ButtonListener buttonListener = new ButtonListener();
button.setOnClickListener(buttonListener);
/*if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment()).commit();
}*/
}
