我尝试以编程方式将属性AlignParentRight设置为RelativeLayout中的按钮,但程序崩溃时出现NullPointerException。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);
我的问题在哪里?错误发生在程序行layoutParams.addRule(RelativeLayout.ALIGN_PARENT_RIGHT);
更新解决方案:
此代码适用于我:
// 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);
答案 0 :(得分:14)
替换
RelativeLayout.LayoutParams layoutParams =(RelativeLayout.LayoutParams)b.getLayoutParams();
带
RelativeLayout.LayoutParams layoutParams = new RelativeLayout.LayoutParams(
RelativeLayout.LayoutParams.MATCH_PARENT,
RelativeLayout.LayoutParams.WRAP_CONTENT);
答案 1 :(得分:8)
当您致电b.getLayoutParams()
时,b不在布局中。因此,它没有layoutparams(另外,它不会知道你现在期待RelativeLayout.LayoutParams)。
您需要创建一个新的LayoutParams实例,就像您为TextView所做的那样。