在RelativeLayout中以編程方式將屬性AlignParentRight設置爲按鈕不起作用？

Question

我嘗試以編程方式將屬性AlignParentRight設置爲RelativeLayout中的按鈕，但程序崩潰時發生NullPointerException。在這裏我的代碼：

//add horizontal realative layout 
RelativeLayout layouth = new RelativeLayout(this); 
layouth.setLayoutParams(new RelativeLayout.LayoutParams(
     LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT)); 

//add textview for label 
TextView t = new TextView(this); 
t.setText(d.getName()); 
t.setTextSize(25); 
t.setId(2);  
t.setLayoutParams(new RelativeLayout.LayoutParams(
     LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT)); 

//add button 
Button b = new Button(this); 
b.setText(d.getName()); 
RelativeLayout.LayoutParams layoutParams =(RelativeLayout.LayoutParams)b.getLayoutParams(); 
layoutParams.addRule(RelativeLayout.ALIGN_PARENT_RIGHT); 
layoutParams.addRule(RelativeLayout.LEFT_OF, 2); 
b.setLayoutParams(layoutParams); 

//add textview and button to horizontal linear layout 
layouth.addView(t); 
layouth.addView(b); 
//add horizontal linear layout to vertical linear layout 
layoutv = (LinearLayout) findViewById(R.id.ProjectViewLinearID); 
layoutv.addView(layouth); 

我的問題在哪裏？在程序行出現的錯誤與Solution layoutParams.addRule(RelativeLayout.ALIGN_PARENT_RIGHT);

UPDATE：

此代碼的工作對我來說：

// Creating a new RelativeLayout 
RelativeLayout layouth = new RelativeLayout(this); 

// Defining the RelativeLayout layout parameters. 
// In this case I want to fill its parent 
RelativeLayout.LayoutParams rlp = new RelativeLayout.LayoutParams(
     RelativeLayout.LayoutParams.MATCH_PARENT, 
     RelativeLayout.LayoutParams.MATCH_PARENT); 

// Creating a new TextView 
TextView tv = new TextView(this); 
tv.setText(d.getName()); 
tv.setTextSize(25); 

//add button 
Button b = new Button(this); 
b.setText(d.getName()); 

// Defining the layout parameters of the TextView 
RelativeLayout.LayoutParams lp = new RelativeLayout.LayoutParams(
     RelativeLayout.LayoutParams.WRAP_CONTENT, 
     RelativeLayout.LayoutParams.WRAP_CONTENT); 
     lp.addRule(RelativeLayout.ALIGN_PARENT_RIGHT); 

// Setting the parameters on the TextView 
tv.setLayoutParams(lp); 
b.setLayoutParams(lp); 

// Adding the TextView to the RelativeLayout as a child 
layouth.addView(tv); 
layouth.addView(b); 

Answer 1

當你調用b.getLayoutParams()，b未在佈局。因此，它沒有layoutparams（另外，它不會知道您期望在此處使用RelativeLayout.LayoutParams）。

您需要創建一個新的LayoutParams實例，就像您爲TextView所做的那樣。

Answer 2

更換

RelativeLayout.LayoutParams layoutParams =(RelativeLayout.LayoutParams)b.getLayoutParams(); 

與

RelativeLayout.LayoutParams layoutParams = new RelativeLayout.LayoutParams(
       RelativeLayout.LayoutParams.MATCH_PARENT, 
       RelativeLayout.LayoutParams.WRAP_CONTENT);