设置视图对象参数和QUOT;高度和宽度QUOT;应用程序崩溃使用空引用错误 [英] Setting view object parameters "height and width" crashes app with null reference error

问题描述

我想一个新的视图添加到我的线性布局 activity_main.xml中

 ＆LT; LinearLayout中的xmlns：机器人=htt​​p://schemas.android.com/apk/res/android
    的xmlns：工具=htt​​p://schemas.android.com/tool​​s
    机器人：layout_width =match_parent
    机器人：layout_height =match_parent
    机器人：paddingLeft =0dp
    机器人：paddingRight =0dp
    机器人：paddingTop =0dp
    机器人：paddingBottom会=0dp
    工具：上下文=。MainActivity
    机器人：ID =@ + ID / activity_main
    机器人：方向=垂直＆GT;    ＆LT; ListView控件
        机器人：ID =@ + ID / ListView1的
        机器人：layout_width =match_parent
        机器人：layout_height =match_parent
        机器人：layout_alignParentBottom =真
        机器人：layout_alignParentLeft =真
        机器人：layout_alignParentStart =真/＆GT;＆LT; / LinearLayout中＆GT;
 

使用这个code

  @覆盖
    保护无效的onCreate（捆绑savedInstanceState）{
        super.onCreate（savedInstanceState）;
        的setContentView（R.layout.activity_main）;        //创建并添加新的视图activity_main
        的LinearLayout activityMain =（的LinearLayout）findViewById（R.id.activity_main）;
        查看playControlsPanelMinimized =新的视图（本）;
        activityMain.addView（playControlsPanelMinimized）;
 

然而，当我尝试设置高度和宽度

  //设置宽度和高度code
    ViewGroup.LayoutParams PARAMS = playControlsPanelMinimized.getLayoutParams（）;
    params.height = 10;
    params.width = 10;
 

通过产生的code

  @覆盖
    保护无效的onCreate（捆绑savedInstanceState）{
        super.onCreate（savedInstanceState）;
        的setContentView（R.layout.activity_main）;        //创建并添加新的视图activity_main
        的LinearLayout activityMain =（的LinearLayout）findViewById（R.id.activity_main）;
        查看playControlsPanelMinimized =新的视图（本）;
        ViewGroup.LayoutParams PARAMS = playControlsPanelMinimized.getLayoutParams（）;        //设置宽度和高度code
        ViewGroup.LayoutParams PARAMS = playControlsPanelMinimized.getLayoutParams（）;
        params.height = 10;
        params.width = 10;        activityMain.addView（playControlsPanelMinimized）;
 

在此应用崩溃启动，并在日志猫以下错误

 了java.lang.RuntimeException：无法启动活动...
 显示java.lang.NullPointerException：尝试写入到外地'廉政
 在一个空对象引用android.view.ViewGroup $ LayoutParams.height
 

在换句话说， PARAMS 对象为空，我不能写入。我认为这是改变视图对象的高度和宽度的正确方法。

修改

这是个人建议我改变相应的高度和宽度

  playControlsPanelMinimized.setLayoutParams（新ViewGroup.LayoutParams（100，100））;
 

虽然应用程序不再崩溃启动时用这种方法，我没有看到新的视图。

修改

我添加了一个背景颜色，但仍我没有看到视图

  playControlsPanelMinimized.setBackgroundColor（Color.parseColor（＃00FFFF））;
 

解决方案

您可以试试，

  playControlsPanelMinimized.setLayoutParams（新ViewGroup.LayoutParams（10，10））;
 

而不是

  ViewGroup.LayoutParams PARAMS = playControlsPanelMinimized.getLayoutParams（）;        //设置宽度和高度code
        ViewGroup.LayoutParams PARAMS = playControlsPanelMinimized.getLayoutParams（）;
        params.height = 10;
        params.width = 10;
 

您可以aother线性布局，并注入新的UI元素到而不是父母的LinearLayout。

 ＆LT; LinearLayout中的xmlns：机器人=htt​​p://schemas.android.com/apk/res/android
    的xmlns：工具=htt​​p://schemas.android.com/tool​​s
    机器人：layout_width =match_parent
    机器人：layout_height =match_parent
    机器人：paddingLeft =0dp
    机器人：paddingRight =0dp
    机器人：paddingTop =0dp
    机器人：paddingBottom会=0dp
    工具：上下文=。MainActivity
    机器人：ID =@ + ID / activity_main
    机器人：方向=垂直＆GT;    ＆LT;！ - 这里有另一个线性布局 - ＆GT;    ＆LT; ListView控件
        机器人：ID =@ + ID / ListView1的
        机器人：layout_width =match_parent
        机器人：layout_height =match_parent
        机器人：layout_alignParentBottom =真
        机器人：layout_alignParentLeft =真
        机器人：layout_alignParentStart =真/＆GT;＆LT; / LinearLayout中＆GT;
 

I am trying to add a new view to my linear layout activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingLeft="0dp"
    android:paddingRight="0dp"
    android:paddingTop="0dp"
    android:paddingBottom="0dp"
    tools:context=".MainActivity"
    android:id="@+id/activity_main"
    android:orientation="vertical">

    <ListView
        android:id="@+id/listView1"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_alignParentBottom="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"/>

</LinearLayout>

Using this code

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Create and add new view to activity_main
        LinearLayout activityMain = (LinearLayout)findViewById(R.id.activity_main);
        View playControlsPanelMinimized = new View(this);
        activityMain.addView(playControlsPanelMinimized);

However, When I try to set the height and width

    // Set height and width code
    ViewGroup.LayoutParams params = playControlsPanelMinimized.getLayoutParams();
    params.height = 10;
    params.width = 10;

With the resulting code

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Create and add new view to activity_main
        LinearLayout activityMain = (LinearLayout)findViewById(R.id.activity_main);
        View playControlsPanelMinimized = new View(this);
        ViewGroup.LayoutParams params = playControlsPanelMinimized.getLayoutParams();

        // Set height and width code
        ViewGroup.LayoutParams params = playControlsPanelMinimized.getLayoutParams();
        params.height = 10;
        params.width = 10;

        activityMain.addView(playControlsPanelMinimized);

The app crashes on start up, with the following error in the log cat

 java.lang.RuntimeException: Unable to start activity ...
 java.lang.NullPointerException: Attempt to write to field 'int
 android.view.ViewGroup$LayoutParams.height' on a null object reference

In other words, the params object is null, and I cannot write to it. I thought this was the correct way to change height and width of a view object.

edit

An individual suggested I change height and width accordingly

playControlsPanelMinimized.setLayoutParams(new ViewGroup.LayoutParams(100, 100)); 

Although the app no longer crashes on startup with this method, I do not see the new view.

edit

I have added a background color but still I see no view

 playControlsPanelMinimized.setBackgroundColor(Color.parseColor("#00FFFF"));

解决方案

You can try,

playControlsPanelMinimized.setLayoutParams(new ViewGroup.LayoutParams(10, 10));

instead of

        ViewGroup.LayoutParams params = playControlsPanelMinimized.getLayoutParams();

        // Set height and width code
        ViewGroup.LayoutParams params = playControlsPanelMinimized.getLayoutParams();
        params.height = 10;
        params.width = 10;

You can have aother linear layout and inject your new UI element to that rather than the parent LinearLayout.

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingLeft="0dp"
    android:paddingRight="0dp"
    android:paddingTop="0dp"
    android:paddingBottom="0dp"
    tools:context=".MainActivity"
    android:id="@+id/activity_main"
    android:orientation="vertical">

    <!-- Have another linear layout here-->

    <ListView
        android:id="@+id/listView1"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_alignParentBottom="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"/>

</LinearLayout>

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