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3、Activity的生命周期

4、学习 ListView

• 4.1 以 MainActivity为默认启动界面，并实现3秒跳转

  public class MainActivity extends AppCompatActivity {
           Handler mHandler = new Handler(); // 创建一个 Handler对象    @Override    protected void onCreate(Bundle savedInstanceState) {
               super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);  	          // 发送一个可执行对象        mHandler.postDelayed(new Runnable() {
                   @Override            public void run() {
                       // 跳转到 ListViewActivity                Intent intent = new Intent(MainActivity.this, ListViewActivity.class);                startActivity(intent);            }        }, 3000);// 3秒后跳转    }}

• 4.2 创建一个 UserInfo类

  public class UserInfo implements Serializable {
           private String mUsername;    private Integer mAge;    private String avatar;    public UserInfo() {
           }    public UserInfo(String mUsername, Integer mAge) {
               this.mUsername = mUsername;        this.mAge = mAge;    }    public String getmUsername() {
               return mUsername;    }    public void setmUsername(String mUsername) {
               this.mUsername = mUsername;    }    public Integer getmAge() {
               return mAge;    }    public void setmAge(Integer mAge) {
               this.mAge = mAge;    }    public String getAvatar() {
               return avatar;    }    public void setAvatar(String avatar) {
               this.avatar = avatar;    }}

• 4.3 在 res/layout下新建一个 activity_listview.xml文件

  

• 4.4 新建一个 ListViewActivity，并添加列表数据，再加入到AndroidManifest.xml中

  public class ListViewActivity extends Activity {
           private ListView mPhoneBookListView;    private List
       
         mUserInfos;    @Override    protected void onCreate(@Nullable Bundle savedInstanceState) {
               super.onCreate(savedInstanceState);        setContentView(R.layout.activity_listview);        mPhoneBookListView = findViewById(R.id.list_view);        mUserInfos = new ArrayList<>();        mUserInfos.add(new UserInfo("小明", 16));        mUserInfos.add(new UserInfo("小红", 17));        mUserInfos.add(new UserInfo("小李", 18));        mUserInfos.add(new UserInfo("小芳", 19));        mUserInfos.add(new UserInfo("小黄", 20));        PhoneBookAdapter phoneBookAdapter = new PhoneBookAdapter(ListViewActivity.this, mUserInfos);        mPhoneBookListView.setAdapter(phoneBookAdapter);        // 设置点击事件        mPhoneBookListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                   @Override            public void onItemClick(AdapterView
         parent, View view, int position, long id) {
                       Toast.makeText(ListViewActivity.this,                     mUserInfos.get(position).getmUsername() + "被点击了", Toast.LENGTH_SHORT).show();            }        });        // 设置长按事件        mPhoneBookListView.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
                   @Override            public boolean onItemLongClick(AdapterView
         parent, View view, int position, long id) {
                       Toast.makeText(ListViewActivity.this,                     mUserInfos.get(position).getmUsername() + "被长按了", Toast.LENGTH_SHORT).show();                return false;            }        });    }}
       

• 4.5 构造桥梁，创建 PhoneBookAdapter类，并创建 item_phonebook.xml文件

  public class PhoneBookAdapter extends BaseAdapter {
           private Context mContext; // 声明 Context上下文    private LayoutInflater mLayoutInflater; // 声明 LayoutInflater：加载布局管理器    private List
       
         mUserInfos = new ArrayList<>(); // 创建 UserInfo集合	    // 创建一个构造器，初始化数据    public PhoneBookAdapter(Context context, List
        
          userInfos) {
               mContext = context;        mUserInfos = userInfos;        mLayoutInflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);    }    @Override    public int getCount() {
               // 有多少条数据        return mUserInfos.size();    }    @Override    public Object getItem(int position) {
               // 返回某一条数据对象        return mUserInfos.get(position);    }    @Override    public long getItemId(int position) {
               // 每一条数据的ID        return position;    }    @Override    public View getView(int position, View convertView, ViewGroup parent) {
               // 返回一个视图        // 将 xml布局文件转换为 View对象，并将 item_phonebook视图中的每一条item解析出来        convertView = mLayoutInflater.inflate(R.layout.item_phonebook, null);        // 获取控件        TextView nameTextView = convertView.findViewById(R.id.name_text_view);        TextView ageTextView = convertView.findViewById(R.id.age_text_view);        ImageView avatarImageView = convertView.findViewById(R.id.avatar_text_view);        // 和数据之间进行绑定        nameTextView.setText(mUserInfos.get(position).getmUsername());        ageTextView.setText(String.valueOf(mUserInfos.get(position).getmAge()));        avatarImageView.setImageResource(R.drawable.phonebook);        return convertView;    }}
        
       

  

• 4.6 效果预览

  

本节学习内容就到这里了。学习地址：https://www.bilibili.com/video/av89274094

转载地址：http://eziwi.baihongyu.com/