设置LayoutParams时出现空指针异常

Question

我在programmaticaly中创建了按钮,而不是在xml文件中.然后我想在这个链接中设置LayoutParams:如何以编程方式设置相对布局中按钮的layout_align_parent_right属性？

但是当我试图发射时,我有一个例外.

这是我的代码:

RelativeLayout ll2 = new RelativeLayout(this);
    //ll2.setOrientation(LinearLayout.HORIZONTAL);

    ImageButton go = new ImageButton(this);
    go.setId(cursor.getInt(cursor.getColumnIndex("_id")));
    go.setClickable(true);
    go.setBackgroundResource(R.drawable.go);
    RelativeLayout.LayoutParams params1 = (RelativeLayout.LayoutParams)go.getLayoutParams();
    params1.addRule(RelativeLayout.ALIGN_PARENT_RIGHT); // LogCat said I have Null Pointer Exception in this line
    go.setLayoutParams(params1);
    go.setOnClickListener(new OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent i3 = new Intent(RecipesActivity.this, MedicineActivity.class);
            i3.putExtra(ShowRecipe, v.getId());
            i3.putExtra("Activity", "RecipesActivity");
            RecipesActivity.this.startActivity(i3);
        }
    });
    ll2.addView(go);

为什么我的应用会抛出异常？谢谢.

Answer 1

改变这个:

RelativeLayout.LayoutParams params1 = (RelativeLayout.LayoutParams)go.getLayoutParams();
params1.addRule(RelativeLayout.ALIGN_PARENT_RIGHT);
go.setLayoutParams(params1);

对于:

RelativeLayout.LayoutParams params1 = new RelativeLayout.LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);
params1.addRule(RelativeLayout.ALIGN_PARENT_RIGHT);
go.setLayoutParams(params1);

以编程方式创建视图时,它没有任何LayoutParams,这就是您获得NullPointerException的原因.如果从XML中扩展视图,那么现在将使用LayoutParams来查看视图.