Question

我现在在这个问题上花了4个多小时，我无法解决它！这是我的Java类：

public class Broken extends Activity implements View.OnClickListener {

    @Override
    protected void onResume() {
        super.onResume();
        final Globals g = (Globals)getApplication();
        super.onResume();

        View decorView = getWindow().getDecorView();
        decorView.setSystemUiVisibility(View.SYSTEM_UI_FLAG_LAYOUT_STABLE
                | View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION
                | View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN
                | View.SYSTEM_UI_FLAG_HIDE_NAVIGATION
                | View.SYSTEM_UI_FLAG_FULLSCREEN
                | View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY);
    }

    protected void onPause() {
        super.onPause();
    }

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        final Globals g = (Globals)getApplication();

        getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);

        View decorView = getWindow().getDecorView();
        decorView.setSystemUiVisibility(View.SYSTEM_UI_FLAG_LAYOUT_STABLE
                | View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION
                | View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN
                | View.SYSTEM_UI_FLAG_HIDE_NAVIGATION
                | View.SYSTEM_UI_FLAG_FULLSCREEN
                | View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY);

        ScreenLayout();
    }


    public void ScreenLayout() {
        final Globals g = (Globals)getApplication();
        int screenHeight = (g.getScreenHeight());
        int screenWidth = (g.getScreenWidth());
        ImageView hmbg = (ImageView) this.findViewById(R.id.mapBackground);
        final float SCALE = getResources().getDisplayMetrics().density;
        int screenHeightDensity = (g.getScreenHeightDensity());
        int screenWidthDensity = (g.getScreenWidthDensity());

        RelativeLayout.LayoutParams btnBackgroundParams = new RelativeLayout.LayoutParams(hmbg.getLayoutParams());
        btnBackgroundParams.topMargin = 100;
        btnBackgroundParams.leftMargin = 100;
        btnBackgroundParams.height = 50;
        btnBackgroundParams.width = 50;
        hmbg.setLayoutParams(btnBackgroundParams);
    }

到目前为止非常简单的东西。这是我的XML文件：

RelativeLayout 
    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"
    android:orientation="horizontal"
    tools:context=".MainActivity"
    android:id="@+id/Form_HordeMap">

    <ImageView
        android:id="@+id/mapBackground"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:background="@drawable/bg_green">
    </ImageView>


</RelativeLayout>

每次启动此活动时应用程序都会崩溃，因为行：

RelativeLayout.LayoutParams btnBackgroundParams = new RelativeLayout.LayoutParams(hmbg.getLayoutParams());

抛出空指针异常。

我一直在阅读无数的论坛。我已经完成了100次这段代码，看不到我错过的任何内容。我只是无法通过这个问题。请帮助我，这样我就可以继续我的生活！

编辑：这里要求的是错误消息：

AndroidRuntime：FATAL EXCEPTION：主要   进程：rule02.touchpool，PID：31822   java.lang.RuntimeException：无法启动活动

ComponentInfo {rule02.touchpool / rule02.touchpool.HordeMap}：

java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法'android.view.ViewGroup $ LayoutParams android.widget.ImageView.getLayoutParams（）'

Answer 1

您没有为Activity设置布局。你必须使用setContentView例如

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.layoutId);
    ScreenLayout();
}

简单形式的空指针异常

1 个答案: