package com.example.thirdweek;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
public class MainActivity extends FragmentActivity {
	private Fragment myMusic;
	private Fragment downLoad;
	private Fragment mine;
private Fragment currentFragment;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		// 获取控件
		Button btnMyMusic = (Button) findViewById(R.id.btn_my_music);
		Button btnDownLoad = (Button) findViewById(R.id.btn_download);
		Button btnMine = (Button) findViewById(R.id.btn_mine);
btnMyMusic.setOnClickListener(new OnClickListener() {
			@Override
			public void onClick(View v) {
				if(myMusic == null){
					myMusic = new MyMusic();
				}
				JumpFragment(myMusic,"music");
			}
		});
btnDownLoad.setOnClickListener(new OnClickListener() {
			@Override
			public void onClick(View v) {
				if(downLoad == null){
					downLoad = new DwonLoad();
				}
				JumpFragment(downLoad,"downLoad");
			}
		});
btnMine.setOnClickListener(new OnClickListener() {
			@Override
			public void onClick(View v) {
				if(mine == null){
					mine = new Mine();
				}
				JumpFragment(mine,"mine");
			}
		});
}
	private void JumpFragment(Fragment fragment, String tab) {
		FragmentManager manager = getSupportFragmentManager();
		FragmentTransaction action = manager.beginTransaction();
		if (!fragment.isAdded()) {
			action.add(R.id.fm, fragment);
		}
		if (currentFragment != null) {
			action.hide(currentFragment);
		}
		action.show(fragment);
		// 添加到回收栈
		action.addToBackStack(tab);
		action.commit();
		currentFragment = fragment;
	}
}
//建造多个数据库需要
db.execSQL("drop if table exists t_user");
原文:http://www.cnblogs.com/bwandroid/p/5551744.html