Android 以编程方式将属性AlignParentRight 设置为RelativeLayout 中的按钮不起作用？
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Programmatically set attribute AlignParentRight to button in RelativeLayout is not working?
提问by Mokkapps
I try to programmatically set the attribute AlignParentRight to button in RelativeLayout but the program crashes with a NullPointerException. Here my code:
我尝试以编程方式将 AlignParentRight 属性设置为 RelativeLayout 中的按钮，但程序因 NullPointerException 而崩溃。这是我的代码：
//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);
Where is my problem? The error occurs in the program line layoutParams.addRule(RelativeLayout.ALIGN_PARENT_RIGHT);
我的问题在哪里？错误发生在程序行layoutParams.addRule(RelativeLayout.ALIGN_PARENT_RIGHT);
UPDATE WITH SOLUTION:
更新解决方案：
This code works for me:
这段代码对我有用：
// 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);
采纳答案by njzk2
When you call b.getLayoutParams(), b is not in a layout. therefore, it does not have a layoutparams (plus, it wouldn't know that you are expecting a RelativeLayout.LayoutParams at this point).
当您调用 时b.getLayoutParams()， b 不在布局中。因此，它没有 layoutparams（此外，它不会知道此时您正在期待一个 RelativeLayout.LayoutParams）。
You need to create a new LayoutParams instance, like you did for the TextView.
您需要创建一个新的 LayoutParams 实例，就像您为 TextView 所做的那样。
回答by Mukesh Soni
replace
代替
RelativeLayout.LayoutParams layoutParams =(RelativeLayout.LayoutParams)b.getLayoutParams();
with
和
RelativeLayout.LayoutParams layoutParams = new RelativeLayout.LayoutParams(
RelativeLayout.LayoutParams.MATCH_PARENT,
RelativeLayout.LayoutParams.WRAP_CONTENT);
