如何在java中代替xml编写相对布局？

Question

我想通过使用Java代码而不是XML文件来运行应用程序。
该应用程序不能在我的手机/模拟器上工作，每次都会崩溃。

的代码看起来是这样的：

package com.nikhil.relativelayoutjavacode; 

import android.support.v7.app.ActionBarActivity;  
import android.os.Bundle;  
import android.view.Menu;  
import android.view.MenuItem;  
import android.widget.Button;  
import android.widget.EditText;  
import android.widget.RelativeLayout;  
import android.widget.RelativeLayout.LayoutParams;  
import android.widget.TextView;  

public class MainActivity extends ActionBarActivity { 

    RelativeLayout main; 
    EditText userNameValue, passwordValue; 
    TextView message, userName, password; 
    LayoutParams messageDimensions; 
    Button login; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 

     init(); 
     createMessageTextView(); 
     main.addView(message, messageDimensions); 
     setContentView(main); 
    } 

    private void init() { 
     // TODO Auto-generated method stub 
     main = new RelativeLayout(this); 
     LayoutParams mainDimensions = new LayoutParams(
       LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT); 
     main.setLayoutParams(mainDimensions); 

     userNameValue = new EditText(this); 
     passwordValue = new EditText(this); 
     message = new TextView(this); 
     userName = new TextView(this); 
     password = new TextView(this); 
     login = new Button(this); 

    } 

    private void createMessageTextView() { 
     LayoutParams messageDimensions = new LayoutParams(
       LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT); 
     messageDimensions.addRule(RelativeLayout.ALIGN_PARENT_LEFT); 
     message.setText("Please Login First"); 
     message.setLayoutParams(messageDimensions); 
    } 
} 

Answer 1

这里：

main.addView(message, messageDimensions); 

messageDimensions是null因为名字messageDimensions在createMessageTextView()方法创建的LayoutParams新的对象，而不是利用其在声明messageDimensions对象职业水平。

所以，使用：

messageDimensions = new LayoutParams(
        LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT); 
      messageDimensions.addRule(RelativeLayout.ALIGN_PARENT_LEFT); 

在createMessageTextView()方法。