android AlertDialog显示错误 Unable to add window token null is not for an application解决办法

 
  public  
  void onCreate(Bundle savedInstanceState) { 
  
         
  super.onCreate(savedInstanceState); 
  
        setContentView(R.layout.activity_main); 
  
         
  
        findViewById(R.id.button1).setOnClickListener( 
  new Button.OnClickListener() { 
  
             
  
             
  public  
  void onClick(View v) { 
  
                 
  new AlertDialog.Builder(getApplicationContext()) 
  
                .setTitle(R.string.dialogTitle) 
  
                .setMessage(R.string.dialogMessage) 
  
                .setPositiveButton("确定",  
  new DialogInterface.OnClickListener() { 
  
                     
  public  
  void onClick(DialogInterface dialog,  
  int which) { 
  
                        Toast.makeText(getApplicationContext(), "你按了确定。", Toast.LENGTH_SHORT).show(); 
  
                    } 
  
                }).show(); 
  
            } 
  
        }); 
  
    } 
 

报错：Unable to add window token null is not for an application

  

异常原因：AlertDialog创建语句public AlertDialog.Builder (Context context)中，不能使用getApplicationContext()得到的context，而必须使用Activity，所以解决如下

 

解决办法：

将 new AlertDialog.Builder(getApplicationContext()) 改为 new AlertDialog.Builder(MainActivity.this)

其中MainActivity 为 当前Activity的名称