0 Activity的类文件

发表于 更新于 分类于 阅读次数：

0 Activity的类文件

活动

  • 实例

    1
    2
    3
    4
    5
    6
    7
    8
    9
    10
    11
    12
    13
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button button = (Button)findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Toast.makeText(MainActivity.this, "You click the button", Toast.LENGTH_SHORT).show();
                    finish(); // 销毁一个活动
                sendMessage(v);
            }
        });
    }

  • 创建一个Button对象实例

    1
    Button button = (Button)findViewById(R.id.button);

    findViewById()获取布局中的元素

  • 监听器

    1
    button.setOnClickListener(new View.OnClickListener()
    • 点击按钮将执行监听器中的 OnClick() 方法
    • 将 Toast 显示出来， Toast 的 makeText() 静态方法

  • 显式调用 Intent

    1
    2
    3
    4
    5
    6
    7
    8
      public void sendMessage(View view){
    //        调用显示Intent
          Intent intent = new Intent(this, DisplayMessageActivity.class);
          EditText editText = findViewById(R.id.editText);
          String message = editText.getText().toString();
          intent.putExtra(EXTRA_MESSAGE, message);
          startActivity(intent);
      }
    • 取出数据
      1
      2
      Intent intent = new getIntent();
      String data = intent.getStringExtra(EXTRA_MESSAGE);

  • 给当前活动创建菜单

    1
    2
    3
    4
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.main, menu);
        return super.onCreateOptionsMenu(menu);
    }

    返回True表示允许创建的菜单显示出来

  • 菜单响应事件

    1
    2
    3
    4
    5
    6
    7
    8
    9
    10
    11
    12
    public boolean onOptionsItemSelected(@NonNull MenuItem item) {
        switch(item.getItemId()){
            case R.id.add_item:
                Toast.makeText(this, "You clicked Add", Toast.LENGTH_SHORT).show();
                break;
            case R.id.remove_item:
                Toast.makeText(this, "You clicked Remove", Toast.LENGTH_SHORT).show();
                break;
            default:
        }
        return super.onOptionsItemSelected(item);
    }
    活动的生命周期
    活动的启动模式

    xml文件

    控件

  1. TextView

  2. Button

  3. EditText

  4. ImageView

  5. ProgressBar

  6. AlertDialog

  7. ProgressDialog

    基本布局
    • 线性布局 LinearLayout
    1
    2
    3
    4
    5
    6
    排列方向：android:orientation="horizonal" 或 vertical
    长宽：android:layout_width="wrap_content",
     android:layout_height="wrap_content"
    对齐方式：gravity指定文字在控件中的对齐方式，
         layout_gravity指定控件在布局中的对齐方式
    layout_weight使用比例的方式指定空间大小
    • 相对布局 RelativeLayout
      layout_alignParentLeft…layout_centerInparent, layout_above…layout_toRightOf, layout_alignLeft…leyout_alignButtom

  8. 帧布局 FrameLayout

  9. 百分比布局 PercentFrameLayout
    layout_widthPercent, layout_heightPercent

    创建自定义布局

  • 引入布局
    创建Title.xml， 引入布局：
    <include layout="@layout/title" />
    将系统还自带的标题栏隐藏：

    1
    2
    3
    4
    ActionBar actionBar = getSuportActionBar();
    if(actionBar != Null){
    actionBar.hide();
    }

  • 创建自定义控件
    可以为控件添加功能，如：为按钮添加响应事件
    新建TitleLayout：

    1
    2
    3
    4
    5
    public class TitleLayout extends LinearLayout {
      public TitleLayout(Context context, AttributeSet attrs){
          super(context, attrs);
          LayoutInflater.from(context).inflate(R.layout.title, this);
    }

    在Activity_main.xml中添加代码，引用TitleLayout：

    1
    2
    3
    4
    <com.example.uitest.TitleLayout
      android:layout_width="match_parent"
      android:layout_height="wrap_content"/>
      <!--（包名不可省）-->
ListView 控件和 RecyclerView 控件

  • ListView

    添加控件：

    1
    2
    3
    4
    <ListView
      android:id="@+id/list_view"
      android:layout_width="match_parent"
      android:layout_height="match_parent"/>

    修改ActivitMain：
      适配器：借助适配器传递数组中的数据给ListView。ArrayAdapter通过指定泛型要适配的数据类型，在构造函数中将数据传入，调用setAdapter()将适配器对象传递进去。

    1
    2
    3
    4
    5
    6
    7
    8
    9
    10
    11
    12
    private String[] data = {"a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m",
            "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"
    };
    @Override
    protected 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 = findViewById(R.id.list_view);
        listView.setAdapter(adapter);
    }

  • 定制ListView界面

    • 新建类Fruit,fruit_itme.xml

    • 创建自定义适配器

      1
      2
      3
      4
      5
      6
      7
      8
      9
      10
      11
      12
      13
      14
      15
      16
      17
      public class FruitAdapter extends ArrayAdapter<Fruit> {
      private int resourceId;
      public FruitAdapter(Context context, int textViewResourceId,
                          List<Fruit> objects){
          super(context, textViewResourceId, objects);
          resourceId = textViewResourceId;
        }
      public View getView(int position, View convertView, ViewGroup parent){
          Fruit fruit = getItem(position);
          View view = LayoutInflater.from(getContext()).inflate(resourceId, parent, false);
          ImageView fruitImage = view.findViewById(R.id.fruit_image);
          TextView fruitName = view.findViewById(R.id.fruit_name);
          fruitImage.setImageResource(fruit.getImageId());
          fruitName.setText(fruit.getName());
          return view;
        } // getView 在每个子项滚动到屏幕内的时候调用
      }

    • 修改 MainActivity

      1
      2
      3
      4
      5
      6
      7
      8
      9
      10
      11
      public class MainActivity extends AppCompatActivity {
      private List<Fruit> fruitList = new ArrayList<>();
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
          initFruits();
          FruitAdapter adapter = new FruitAdapter(MainActivity.this, R.layout.fruit_item, fruitList);
          ListView listView = findViewById(R.id.list_view);
          listView.setAdapter(adapter);
      }}

    • 提升ListView运行效率

      • 修改getView()：convertView布局的缓存
        1
        2
        3
        4
        5
        6
        7
        View view;
        if(convertView == null) {
                view = LayoutInflater.from(getContext()).inflate(resourceId, parent, false);
        }
        else {
            view = convertView;
        }
      • 修改getView()：viewHolder对控件实例的缓存
        1
        2
        3
        4
            class ViewHolder{
            ImageView fruitImage;
            TextView fruitName;
        }
        1
        2
        3
        4
        5
        6
        7
        8
        9
        10
        11
        12
        13
        14
        15
        16
        View view;
        ViewHolder viewHolder;
        if(convertView == null) {
                view = LayoutInflater.from(getContext()).inflate(resourceId, parent, false);
                viewHolder = new ViewHolder();
                viewHolder.fruitImage = view.findViewById(R.id.fruit_image);
                viewHolder.fruitName = view.findViewById(R.id.fruit_name);
                view.setTag(viewHolder); //viewHolder存储在view中
        }
        else {
            view = convertView;
            viewHolder = (ViewHolder) view.getTag();
        }
        viewHolder.fruitImage.setImageResource(fruit.getImageId());
        viewHolder.fruitName.setText(fruit.getName());
        return view;
      • ListView 点击事件
        1
        2
        3
        4
        5
        6
        listView.setOnItemClickListener(new AdapterView.OnItemClickListener(){
        public void onItemClick(AdapterView<?>parent, View view, int position, long id){
                  Fruit fruit = fruitList.get(position);
                  Toast.makeText(MainActivity.this, fruit.getName(), Toast.LENGTH_SHORT).show();
              }
          });

  • RecyclerView

    • FruitAdapter文件
      1
      2
      3
      4
      5
      6
      7
      8
      9
      10
      11
      12
      13
      14
      15
      16
      17
      18
      19
      20
      21
      22
      23
      24
      25
      26
      27
      28
      29
      30
      31
      32
      33
      34
      35
      36
      37
      38
      39
      public class FruitAdapter extends RecyclerView.Adapter<FruitAdapter.ViewHolder> {

        private List<Fruit> mFruitList;


        static class ViewHolder extends RecyclerView.ViewHolder{
            ImageView fruitImage;
            TextView fruitName;

            public ViewHolder(@NonNull View view) {
                super(view);
                fruitName = (TextView)view.findViewById(R.id.fruit_name);
                fruitImage = (ImageView)view.findViewById(R.id.fruit_image);
            }
        }
        public FruitAdapter(List<Fruit> fruitList){
            mFruitList = fruitList;
        }

        @NonNull
        @Override
        public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
            View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.fruit_item, parent, false);
            ViewHolder holder = new ViewHolder(view);
            return holder;
        }

        @Override
        public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
            Fruit fruit = mFruitList.get(position);
            holder.fruitImage.setImageResource(fruit.getImageId());
            holder.fruitName.setText(fruit.getName());
        }

        @Override
        public int getItemCount() {
            return mFruitList.size();
        }
      }
    • MainActivity文件
      1
      2
      3
      4
      5
      6
      7
      8
      9
      10
          protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
          initFruits();
          RecyclerView recyclerView = findViewById(R.id.recycler_view);
          LinearLayoutManager layoutManager = new LinearLayoutManager(this);
          recyclerView.setLayoutManager(layoutManager);
          FruitAdapter adapter = new FruitAdapter(fruitList);
          recyclerView.setAdapter(adapter);
      }
    • 横向排列(MainActivity) 
      1
      2
      3
      4
      5
      6
      7
      8
      9
      10
      11
        protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
          initFruits();
          RecyclerView recyclerView = findViewById(R.id.recycler_view);
          LinearLayoutManager layoutManager = new LinearLayoutManager(this);
          layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL); //横向排列
          recyclerView.setLayoutManager(layoutManager);
          FruitAdapter adapter = new FruitAdapter(fruitList);
          recyclerView.setAdapter(adapter);
      }
    • 瀑布流布局
      1
      2
      3
      4
      5
      6
      7
      8
      9
      10
      11
      12
      13
        protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
          initFruits();
          RecyclerView recyclerView = findViewById(R.id.recycler_view);
          LinearLayoutManager layoutManager = new LinearLayoutManager(this);
          //瀑布流布局
          StaggeredGridLayoutManager layoutManager = 
                  new StaggeredGridLayoutManager(3, StaggeredGridLayoutManager.VERTICAL);
          recyclerView.setLayoutManager(layoutManager);
          FruitAdapter adapter = new FruitAdapter(fruitList);
          recyclerView.setAdapter(adapter);
      }