Android 安卓DataBinding（九）·运算符

傷城~ 2023-06-03 03:57 10阅读 0赞

### 文章目录 ###

*   *  前景回顾
     *  运算符
     *  使用方法
     *   *  算术运算符
         *  字符串合并操作
         *  ??运算符
         *  布局文件属性控制

--------------------

## 前景回顾 ##

[Android 安卓DataBinding（一）·基础][Android _DataBinding]  
[Android 安卓DataBinding（二）·入门][Android _DataBinding 1]  
[Android 安卓DataBinding（三）·单向绑定 BaseObservable][Android _DataBinding_ BaseObservable]  
[Android 安卓DataBinding（四）·单向绑定 ObservableField][Android _DataBinding_ ObservableField]  
[Android 安卓DataBinding（五）·单向绑定 ObservableCollection（集合使用）][Android _DataBinding_ ObservableCollection]  
[Android 安卓DataBinding（六）·双向绑定][Android _DataBinding 2]  
[Android 安卓DataBinding（七）·事件绑定][Android _DataBinding 3]  
[Android 安卓DataBinding（八）·引用类方法][Android _DataBinding 4]

--------------------

## 运算符 ##

本篇讲的是在布局文件中使用运算符：

<table> 
 <thead> 
  <tr> 
   <th>运算符类型</th> 
   <th>运算符号</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>算术运算符</td> 
   <td>+ - * / %</td> 
  </tr> 
  <tr> 
   <td>字符串合并操作</td> 
   <td>+</td> 
  </tr> 
  <tr> 
   <td>逻辑运算符</td> 
   <td>&amp;&amp; II</td> 
  </tr> 
  <tr> 
   <td>一元运算符</td> 
   <td>+ - ！～</td> 
  </tr> 
  <tr> 
   <td>二元运算符</td> 
   <td>&amp; I ^</td> 
  </tr> 
  <tr> 
   <td>三元运算符</td> 
   <td>?:</td> 
  </tr> 
  <tr> 
   <td>移位运算符</td> 
   <td>&gt;&gt; &gt;&gt;&gt; &lt;&lt;</td> 
  </tr> 
  <tr> 
   <td>比较运算符</td> 
   <td>&gt; &lt; = &gt;= &lt;= ==</td> 
  </tr> 
  <tr> 
   <td>…</td> 
   <td>…</td> 
  </tr> 
 </tbody> 
</table>

--------------------

## 使用方法 ##

接下来来介绍上面的运算符的使用方法，给出代码实例！

--------------------

### 算术运算符 ###

举例：  
写出布局文件：  
因为是int类型，所以要用 String.valueOf()

<?xml version="1.0" encoding="utf-8"?>
    <layout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools">
    
        <data>
        
        </data>
    
        <android.support.constraint.ConstraintLayout android:layout_width="match_parent" android:layout_height="match_parent" android:background="#FFFFFF" tools:context=".MainActivity">
    
        <TextView android:layout_width="match_parent" android:layout_height="230dp" android:background="#03A9F4" android:gravity="center" android:text="@{String.valueOf(123+456)}" android:textColor="#FFFFFF" android:textSize="18dp" android:textStyle="bold" app:layout_constraintLeft_toLeftOf="parent" app:layout_constraintRight_toRightOf="parent" app:layout_constraintTop_toTopOf="parent" />
    
        </android.support.constraint.ConstraintLayout>
    </layout>

--------------------

MainActivity.java 中绑定布局

package com.lkdot.tbind;
    
    import android.databinding.DataBindingUtil;
    import android.support.v7.app.AppCompatActivity;
    import android.os.Bundle;
    
    import com.lkdot.tbind.databinding.ActivityMainBinding;
    
    public class MainActivity extends AppCompatActivity { 
    
        ActivityMainBinding activityMainBinding;
        
        @Override
        protected void onCreate(Bundle savedInstanceState) { 
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
    
            activityMainBinding = DataBindingUtil.setContentView(this, R.layout.activity_main);
    
        }
    }

--------------------

效果图：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwODgxNjgw_size_16_color_FFFFFF_t_70]  
算术运算符其他的（- \* / %）使用方法都是这样

--------------------

### 字符串合并操作 ###

主要代码：android:text="@\{data.title + data.name\}"

<?xml version="1.0" encoding="utf-8"?>
    <layout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools">
    
        <data>
    
            <import type="com.lkdot.tbind.DataBean" />
    
            <variable name="data" type="DataBean" />
        </data>
    
        <android.support.constraint.ConstraintLayout android:layout_width="match_parent" android:layout_height="match_parent" android:background="#FFFFFF" tools:context=".MainActivity">
    
        <TextView android:layout_width="match_parent" android:layout_height="230dp" android:background="#03A9F4" android:gravity="center" android:text="@{data.title + data.name}" android:textColor="#FFFFFF" android:textSize="18dp" android:textStyle="bold" app:layout_constraintLeft_toLeftOf="parent" app:layout_constraintRight_toRightOf="parent" app:layout_constraintTop_toTopOf="parent" />
    
        </android.support.constraint.ConstraintLayout>
    </layout>

--------------------

Bean类：

package com.lkdot.tbind;
    
    public class DataBean { 
        private String title;
        private String name;
    
        public DataBean(String title, String name) { 
            this.title = title;
            this.name = name;
        }
    
        public String getTitle() { 
            return title;
        }
    
        public void setTitle(String title) { 
            this.title = title;
        }
    
        public String getName() { 
            return name;
        }
    
        public void setName(String name) { 
            this.name = name;
        }
    }

--------------------

MainActivity中绑定

package com.lkdot.tbind;
    
    import android.databinding.DataBindingUtil;
    import android.support.v7.app.AppCompatActivity;
    import android.os.Bundle;
    
    import com.lkdot.tbind.databinding.ActivityMainBinding;
    
    public class MainActivity extends AppCompatActivity { 
    
        ActivityMainBinding activityMainBinding;
        DataBean textData;
    
        @Override
        protected void onCreate(Bundle savedInstanceState) { 
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
    
            activityMainBinding = DataBindingUtil.setContentView(this, R.layout.activity_main);
            textData = new DataBean("Start", "NorthernBrain");
            activityMainBinding.setData(textData);
        }
    }

--------------------

运行效果：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwODgxNjgw_size_16_color_FFFFFF_t_70 1]

--------------------

### ??运算符 ###

?? 运算符会取第一个不是 null 的值。  
![在这里插入图片描述][20191006154907429.jpeg]

android:text="@\{data.title ?? data.name\}"

--------------------

### 布局文件属性控制 ###

他甚至可以用于布局文件属性控制  
android:visibility="@\{data.status ? View.VISIBLE : View.GONE\}"

--------------------

下一片文章：**[Android 安卓DataBinding（十）·include中使用][Android _DataBinding_include]**

[Android _DataBinding]: https://blog.csdn.net/qq_40881680/article/details/101714634
[Android _DataBinding 1]: https://blog.csdn.net/qq_40881680/article/details/101781705
[Android _DataBinding_ BaseObservable]: https://blog.csdn.net/qq_40881680/article/details/101800669
[Android _DataBinding_ ObservableField]: https://blog.csdn.net/qq_40881680/article/details/101847386
[Android _DataBinding_ ObservableCollection]: https://blog.csdn.net/qq_40881680/article/details/101993642
[Android _DataBinding 2]: https://blog.csdn.net/qq_40881680/article/details/102010622
[Android _DataBinding 3]: https://blog.csdn.net/qq_40881680/article/details/102072807
[Android _DataBinding 4]: https://blog.csdn.net/qq_40881680/article/details/102109527
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwODgxNjgw_size_16_color_FFFFFF_t_70]: /images/20230601/93c5b8338119491c836bc4c29b195f88.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwODgxNjgw_size_16_color_FFFFFF_t_70 1]: /images/20230601/61d1ab8aaec44dc2a9704747540d1e30.png
[20191006154907429.jpeg]: /images/20230601/e000487007c34c708eb13e372c545df5.png
[Android _DataBinding_include]: https://blog.csdn.net/qq_40881680/article/details/102239366