java.lang.RuntimeException : Can't create handler inside thread that has not called Looper. 准备()

Question

当单击按钮时，我使用简单的线程执行 httpGet 到服务器，但在执行后我得到了这个。

Button b_back = (Button) findViewById(R.id.bback);
b_back.setOnClickListener(this);
Button b_sign_up = (Button) findViewById(R.id.signup_button);
b_sign_up.setOnClickListener(this);

@Override
public void onClick(View arg0) 
{
    // TODO Auto-generated method stub
    switch (arg0.getId()) 
    {
        case R.id.bback:
            Intent i = new Intent(this, MainSwitch.class);
            finish();
            startActivity(i);
            break;

            // More buttons go here (if any) ...

        case R.id.signup_button:
            if(username.getText().toString().equalsIgnoreCase("") ||
               password.getText().toString().equalsIgnoreCase("") ||
               email.getText().toString().equalsIgnoreCase(""))
            {
                AlertDialog.Builder dialog = new AlertDialog.Builder(this);
                dialog.setMessage("Please fill in all the gaps!");
                dialog.show();
            }
            else
            {
                //****** Call method that sends the information to server.
                Thread background = new Thread (new Runnable() 
                {
                    public void run()
                    {
                        // Call the time consuming method
                        handler.sendEmptyMessage(0);
                    }
                });
                background.start();
            }
    }
}

private Handler handler = new Handler() 
{
    @Override
    public void handleMessage(Message msg) 
    {
        Toast.makeText(getApplicationContext(),
                       "Done thread",
           Toast.LENGTH_SHORT).show();

    }
};

Answer 1

您得到的错误行:

java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()

通常与您尝试在非 UI 线程上对 UI 元素执行操作的问题相关。

我想通过声明//调用耗时的方法你已经遗漏了一些代码。事实上，这个耗时的方法在常规 Thread 上运行，这意味着它无法与 UI 元素交互。

如果您发布更多代码(以及指定发生错误的行)，我们可能可以提供有关如何解决该问题的更多信息。