Android----------实现简单的购物车加减器

1.布局

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
  android:orientation="horizontal">

    <Button
        android:id="@+id/jian"
        android:onClick="onClick"
        android:clickable="true"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="-" />
    <EditText
        android:id="@+id/text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="1"/>
    <Button
        android:id="@+id/add"
        android:onClick="onClick"
        android:clickable="true"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="+" />
LinearLayout>

2. 主界面

public class MainActivity extends AppCompatActivity {
     private Button add,jian;
     private TextView tv;
    private int amount =0; //购买数量
   // private int goods_storage = 1; //商品库存
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        add=(Button)findViewById(R.id.add);
        jian=(Button)findViewById(R.id.jian);
        tv=(TextView)findViewById(R.id.text);
        add.setTag("+");
        jian.setTag("-");
        tv.setInputType(android.text.InputType.TYPE_CLASS_NUMBER);
        tv.setText(String.valueOf(amount));
        SetViewListener();

    }

    private void SetViewListener() {
        add.setOnClickListener(new OnButtonClickListener());
        jian.setOnClickListener(new OnButtonClickListener());
      //  tv.setOnClickListener(new OnTextChangeListener());
    }
    class OnButtonClickListener implements View.OnClickListener{

        @Override
        public void onClick(View v) {
            String s = tv.getText().toString();
          if (s==null||s.equals("")){
              amount=0;
              tv.setText("0");
          }else {
              if (v.getTag().equals("+")){
                  if (++amount < 0){
                      //先加，再判断
                      amount--;
                  }else {
                      tv.setText(String.valueOf(amount));
                  }
              }else if (v.getTag().equals("-")){
                  if (--amount < 0){
                      //先减，再判断
                  amount++;
                  }else {
                      tv.setText(String.valueOf(amount));
                  }

              }
          }

        }
    }


}