Question

我有一个活动，该活动从用户那里获取两个变量（进行体重和次数），然后进行一些计算并通过此意图发送最终结果：

Intent intent = new Intent(this,calculated_2.class);
intent.putExtra("EXTRA_MESSAGE","your calculated one rep max is "+onerepmax+ " KG");
startActivity(intent);

在我的第一次尝试中，我进行了一个Textview的活动，并使用以下代码编辑了Textview：

    Intent intent = getIntent();
    String message = intent.getStringExtra("EXTRA_MESSAGE");
    TextView tv = findViewById(R.id.one);
    tv.setText(message);

但是，我将该活动切换到了选项卡式视图。
这是它的代码：

public class calculated_2 extends AppCompatActivity {

    private static final String TAG = "Calculate";
    private  SectionsPageAdapter spa;
    private ViewPager mviewPager;
    private EditText et;



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_calculated_2);
        Log.d(TAG,"onCreate: Starting. ");


        Intent intent = getIntent();
        String message = intent.getStringExtra("EXTRA_MESSAGE");
        TextView tv = findViewById(R.id.one);
        tv.setText(message);

        spa = new SectionsPageAdapter(getSupportFragmentManager());
        mviewPager =(ViewPager) findViewById(R.id.container);
        setViewPager(mviewPager);

        TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs);
        tabLayout.setupWithViewPager(mviewPager);


    }

    private void setViewPager(ViewPager viewPager){

        SectionsPageAdapter adapter = new SectionsPageAdapter(getSupportFragmentManager());
        adapter.AddFragment(new tab1_fragment(),"One Rep Max");
        adapter.AddFragment(new tab2_fragment(),"5-3-1");
        viewPager.setAdapter(adapter);
    }

}

这是第一个包含该文本视图的选项卡的代码：

public class tab1_fragment extends Fragment {
    private static final String TAG = "oneRepMax";


    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view =inflater.inflate(R.layout.tab1_fragment,container,false);
        return view;


    }


}

但是，with this code im not able to edit the textview and my app crashes.

错误：

E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: com.khedir.ufp, PID: 19412
                  java.lang.RuntimeException: Unable to start activity ComponentInfo{com.khedir.ufp/com.khedir.ufp.calculated_2}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2778)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856)
                      at android.app.ActivityThread.-wrap11(Unknown Source:0)
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589)
                      at android.os.Handler.dispatchMessage(Handler.java:106)
                      at android.os.Looper.loop(Looper.java:164)
                      at android.app.ActivityThread.main(ActivityThread.java:6494)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
                   Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
                      at com.khedir.ufp.calculated_2.onCreate(calculated_2.java:45)
                      at android.app.Activity.performCreate(Activity.java:7009)
                      at android.app.Activity.performCreate(Activity.java:7000)
                      at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1214)
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2731)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856) 
                      at android.app.ActivityThread.-wrap11(Unknown Source:0) 
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589) 
                      at android.os.Handler.dispatchMessage(Handler.java:106) 
                      at android.os.Looper.loop(Looper.java:164) 
                      at android.app.ActivityThread.main(ActivityThread.java:6494) 
                      at java.lang.reflect.Method.invoke(Native Method) 
                      at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)

活动布局：

    <?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/main_content"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context=".calculated_2">

    <android.support.design.widget.AppBarLayout
        android:id="@+id/appbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:paddingTop="@dimen/appbar_padding_top"
        android:theme="@style/AppTheme.AppBarOverlay">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:layout_weight="1"
            android:background="?attr/colorPrimary"
            app:layout_scrollFlags="scroll|enterAlways"
            app:popupTheme="@style/AppTheme.PopupOverlay"
            app:title="@string/app_name">

        </android.support.v7.widget.Toolbar>

        <android.support.design.widget.TabLayout
            android:id="@+id/tabs"
            android:layout_width="match_parent"
            android:layout_height="wrap_content">

            <android.support.design.widget.TabItem
                android:id="@+id/tabItem"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="@string/tab_text_1" />

            <android.support.design.widget.TabItem
                android:id="@+id/tabItem2"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="@string/tab_text_2" />

            <android.support.design.widget.TabItem
                android:id="@+id/tabItem3"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="@string/tab_text_3" />

        </android.support.design.widget.TabLayout>
    </android.support.design.widget.AppBarLayout>

    <android.support.v4.view.ViewPager
        android:id="@+id/container"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior" />



</android.support.design.widget.CoordinatorLayout>

包含TextView的片段布局：

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".calculated_2">

    <TextView
        android:id="@+id/one"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginEnd="24dp"
        android:layout_marginLeft="24dp"
        android:layout_marginRight="24dp"
        android:layout_marginStart="24dp"
        android:layout_marginTop="24dp"
        android:text="Your Calculated 1RM"
        android:textAppearance="@style/TextAppearance.AppCompat.Display1"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</android.support.constraint.ConstraintLayout>

Answer 1

根据日志的建议，您正在null对象引用上使用 setText 方法。

要解决此问题，请确保在布局文件中将TextView包含在id中。

此TextView tv = findViewById(R.id.one);
确保存在ID为one的TextView。

通过意图在选项卡式活动中编辑TextView-Android

1 个答案: