Android,如何获取/设置布局参数?

时间:2013-04-18 09:56:07

标签: android android-layout layoutparams

在我的申请表中,我有一个会话室。我的所有消息都应该正确对齐,而其余消息应保持对齐。

我的列表的单行是这样的:

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/llContainer" >

    <LinearLayout
        android:orientation="vertical"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="5dp"
        android:background="@drawable/speech_bubble_orange"
        android:id="@+id/llGroup" >

            <TextView
                android:id="@+id/message_text"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:shadowColor="@color/message_textShadow"
                android:shadowDx="1"
                android:shadowDy="1"
                android:text="Medium Text"
                android:textColor="@color/message_textColor"
                android:textSize="20sp" />

            <TextView
                android:id="@+id/message_date"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:text="@string/temp_date"
                android:gravity="right"
                android:layout_marginLeft="4dp"
                android:layout_marginRight="4dp"/>
    </LinearLayout>

</LinearLayout>

我的适配器的getView()是这样的:

@Override
public View getView(final int position, View convertView, ViewGroup parent) {
    ViewHolder holder;

    if (convertView == null) {
        convertView = myInflater.inflate(R.layout.list_message_row, null);
        holder = new ViewHolder();

        holder.tvMessageBody = (TextView) convertView.findViewById(R.id.message_text);
        holder.tvMessageDate = (TextView) convertView.findViewById(R.id.message_date);
        holder.llContainer = (LinearLayout) convertView.findViewById(R.id.llContainer);
        holder.llGroup = (LinearLayout) convertView.findViewById(R.id.llGroup);

        convertView.setTag(holder);
    } else {
        holder = (ViewHolder) convertView.getTag();
    }

    holder.tvMessageBody.setText(messageList.get(position).getMessageBody());
    String date = messageList.get(position).getSentDate();
    holder.tvMessageDate.setText(formatFanciedDate(date));

    LinearLayout.LayoutParams params = (LinearLayout.LayoutParams) holder.llContainer.getLayoutParams();
    try {
        if(messageList.get(position).isMine()) {
            holder.llGroup.setBackgroundResource(R.drawable.speech_bubble_green);
            params.gravity = Gravity.RIGHT;
        }
        //If not mine then it is from sender to show orange background and align to left
        else {
            holder.llGroup.setBackgroundResource(R.drawable.speech_bubble_orange);
            params.gravity = Gravity.LEFT;
        }

        holder.llContainer.setLayoutParams(params);

    } catch (NullPointerException e) {
        e.printStackTrace();
    }

    return convertView;
}

我认为一切都应该没问题,但是当我运行应用程序时发生NullPointerException并指向params.gravity = Gravity.RIGHT;params.gravity = Gravity.LEFT;(取决于isMine()方法)。

你怎么想?我的错误在哪里? 任何建议都将不胜感激。

2 个答案:

答案 0 :(得分:8)

getLayoutParams()将返回null,直到视图附加到其父级。

尝试使用其构造函数创建布局参数,而不是使用getLayoutParams()

答案 1 :(得分:7)

使用RelativeLayout params并像这样设置重力,它会起作用。

RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(RelativeLayout.LayoutParams.WRAP_CONTENT, RelativeLayout.LayoutParams.WRAP_CONTENT);
params.addRule(RelativeLayout.ALIGN_PARENT_RIGHT, RelativeLayout.TRUE);

这在我的申请中对我有用。