如何在Android上更改可见的relativelayout？

Question

试图找到解决方案，当我尝试这样做时，程序以某种方式崩溃了。

我的代码有什么问题，找不到执行此操作的任何原因？

无论如何，在程序的其他部分，类似的工作是否正确？

一点点代码来解释我的问题..

my.java

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    switch();
}

public void switch() {
    RelativeLayout chatsLayout = (RelativeLayout)findViewById(R.id.chatsLayout);
    RelativeLayout chats = (RelativeLayout) chatsLayout.findViewById(R.id.chats);
    chats.setVisibility(View.GONE);

    RelativeLayout noChats = (RelativeLayout) chatsLayout.findViewById(R.id.noChats);
    noChats.setVisibility(View.GONE);
}

my.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/chatsLayout"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/white">
    <RelativeLayout
        android:id="@+id/chats"
        android:visibility="gone"
        android:padding="8dp"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent">
    </RelativeLayout>
    <RelativeLayout
        android:id="@+id/noChats"
        android:padding="8dp"
        android:visibility="visible"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent">
    </RelativeLayout>
</RelativeLayout>

这是我从logcat得到的错误代码：

08-10 08:06:00.922    2736-2736/fi.hgs.apps E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: fi.hgs.apps, PID: 2736
java.lang.RuntimeException: Unable to start activity ComponentInfo{fi.hgs.apps/fi.hgs.apps.ChatsActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.widget.RelativeLayout.findViewById(int)' on a null object reference

和这个

 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.widget.RelativeLayout.findViewById(int)' on a null object reference

Answer 1

您的onCreate应该看起来像这样：

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
setContentView(R.layout.your_layout);
    switch();
}

您的switch方法应如下所示：

public void switch() {
    RelativeLayout chatsLayout = (RelativeLayout)findViewById(R.id.chatsLayout);
    RelativeLayout chats = (RelativeLayout)findViewById(R.id.chats);
    chats.setVisibility(View.GONE);

    RelativeLayout noChats = (RelativeLayout)findViewById(R.id.noChats);
    noChats.setVisibility(View.GONE);
}

既然你所有的意见； chatsLayout，chats和noChats是在活动中膨胀的同一xml中定义的，您可以直接在它们上调用findViewById。

Answer 2

在onCreate()调用setContentView()并使用findViewById()查找。 否则，您将获得NullPointerException

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.your_layout);
        switch();
    }