Android动态添加Scrollview-Content

Question

我正在努力为滚动视图动态添加一些内容。如果有人可以给我一个解释，为什么我的应用程序崩溃，我会很感激。

public class LessonView extends AppCompatActivity {
    int maxWidth = 450;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // old
        ScrollView SView = new ScrollView(this);

        // new
        // LinearLayout activityLL = (LinearLayout) findViewById(R.id.myLL);

        RelativeLayout.LayoutParams centerTableParameters = new RelativeLayout.LayoutParams(
                RelativeLayout.LayoutParams.WRAP_CONTENT, RelativeLayout.LayoutParams.WRAP_CONTENT
        );
        centerTableParameters.addRule(RelativeLayout.CENTER_IN_PARENT);

        LinearLayout llayout = new LinearLayout(this);
        llayout.setOrientation(LinearLayout.VERTICAL);
        llayout.setGravity(Gravity.CENTER);

        Resources res  = getResources();

        Intent in = getIntent();
        int index = in.getIntExtra("com.example.ITEM_INDEX", -1);

        if(true){


            // create tables:
            boolean tablesEnd = false;
            boolean lineEnd = false;
            int j = 0;
            int i = 0;
            while(i < cn.length){
                TableLayout tableLayout = new TableLayout(this);
                TableRow tableRow1 = new TableRow(this);
                TableRow tableRow2 = new TableRow(this);
                TableRow tableRow3 = new TableRow(this);
                TableLayout.LayoutParams lp = new TableLayout.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT);

                tableLayout.setLayoutParams(lp);

                // create lines:
                lineEnd = false;
                while(i < cn.length && lineEnd == false){
                     [...]
                }

                tableLayout.addView(tableRow1);
                tableLayout.addView(tableRow2);
                tableLayout.addView(tableRow3);

                llayout.addView(tableLayout, centerTableParameters);
                Space space = new Space(this);
                space.setLayoutParams(new LinearLayout.LayoutParams(10, 20));
                llayout.addView(space);

            }

            // old:
            SView.addView(llayout);
            setContentView(SView);

            // new:
            //activityLL.addView(llayout);
            //setContentView(R.layout.activity_lesson_view);
        }
    }

如果我使用“旧”代码运行它（请参见注释“旧”下面的行），则它运行正常，没有错误。旧代码不使用任何布局文件。我想向布局中添加更多功能；）一旦我以“新”行（旧行作为注释）开始活动，应用程序就会崩溃并显示错误消息：

2019-10-26 23：51：42.694 4599-4599 / com.example.MyApp E / AndroidRuntime：FATAL EXCEPTION：main流程：com.example.MyApp，PID：4599java.lang.RuntimeException：无法启动活动ComponentInfo {com.example.MyApp / com.example.MyApp.LessonView}：java.lang.NullPointerException：尝试调用虚拟方法'void android.widget.LinearLayout.addView（android。 view.View）”上的空对象引用在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2913）在android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:3048）在android.app.servertransaction.LaunchActivityItem.execute（LaunchActivityItem.java:78）在android.app.servertransaction.TransactionExecutor.executeCallbacks（TransactionExecutor.java:108）在android.app.servertransaction.TransactionExecutor.execute（TransactionExecutor.java:68）在android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1808）在android.os.Handler.dispatchMessage（Handler.java:106）在android.os.Looper.loop（Looper.java:193）在android.app.ActivityThread.main（ActivityThread.java:6669）在java.lang.reflect.Method.invoke（本机方法）在com.android.internal.os.RuntimeInit $ MethodAndArgsCaller.run（RuntimeInit.java:493）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:858）原因：java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法'void android.widget.LinearLayout.addView（android.view.View）'在com.example.MyApp.LessonView.onCreate（LessonView.java:242）在android.app.Activity.performCreate（Activity.java:7136）在android.app.Activity.performCreate（Activity.java:7127）在android.app.Instrumentation.callActivityOnCreate（Instrumentation.java:1271）在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2893）在android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:3048）在android.app.servertransaction.LaunchActivityItem.execute（LaunchActivityItem.java:78）在android.app.servertransaction.TransactionExecutor.executeCallbacks（TransactionExecutor.java:108）在android.app.servertransaction.TransactionExecutor.execute（TransactionExecutor.java:68）在android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1808）在android.os.Handler.dispatchMessage（Handler.java:106）在android.os.Looper.loop（Looper.java:193）在android.app.ActivityThread.main（ActivityThread.java:6669）在java.lang.reflect.Method.invoke（本机方法）在com.android.internal.os.RuntimeInit $ MethodAndArgsCaller.run（RuntimeInit.java:493）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:858）。

错误似乎发生在"activityLL.addView(llayout);" (line 242)，但我没有解释为什么...

Answer 1

您应先调用setContentView(R.layout.activity_lesson_view);，然后再使用LinearLayout activityLL = (LinearLayout) findViewById(R.id.myLL);检索LinearLayout，>