Question

我在主要活动中使用TextView作为链接，当我点击此链接时发生错误这是我的活动：（更新）

public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main_activity);

    LayoutInflater inflater = LayoutInflater.from(this);
    View layout= inflater.inflate(R.layout.second_activity, null, false);
    TextView text = (TextView)layout.findViewById(R.id.mapTextView);
    text.setOnClickListener(new View.OnClickListener(){
        @Override
        public void onClick(View v) {
            Intent intent = new Intent(MainActivity.this, SecondActivity.class);
            startActivity(intent);
        }
    });
   }
}

my second_activity.xml：

 <RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal">
    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:gravity="center"
        android:orientation="vertical">
        <TextView
            android:id="@+id/mapTextView"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_margin="5dp"
            android:text="Test Link"
            android:textStyle="bold"
            android:textColor="@color/textcolor"
            android:textSize="14sp" />

    </LinearLayout>

我的适配器类：

public class RecyclerAdapter extends RecyclerView.Adapter<RecyclerAdapter.CustomViewHolder> {
...
@Override
public CustomViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    switch (viewType) {
        case 1:
            View viewONE = LayoutInflater.from(parent.getContext()).inflate(R.layout.first_activity, parent, false);
            CustomViewHolder rowONE = new CustomViewHolder(viewONE);
            return rowONE;

        case 2:
            View viewTWO = LayoutInflater.from(parent.getContext()).inflate(R.layout.second_activity, parent, false);
            CustomViewHolder rowTWO = new CustomViewHolder(viewTWO);
            return rowTWO;
 }

logcat的：

E/AndroidRuntime: FATAL EXCEPTION: main
              Process: com.totoroads.android.app, PID: 5699
              java.lang.RuntimeException: Unable to start activity ComponentInfo{com.totoroads.android.app/com.totoroads.android.app.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
                  at android.app.ActivityThread.-wrap11(ActivityThread.java)
                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
                  at android.os.Handler.dispatchMessage(Handler.java:102)
                  at android.os.Looper.loop(Looper.java:148)
                  at android.app.ActivityThread.main(ActivityThread.java:5417)
                  at java.lang.reflect.Method.invoke(Native Method)
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
               Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
                  at com.totoroads.android.app.MainActivity .onCreate(MainActivity.java:100)
                  at android.app.Activity.performCreate(Activity.java:6237)
                  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)

varialbe mapTextView 我没有在main_activity.xml中设置并在其他（second_activity.xml）中设置

如何在其他布局中调用mapTextView？谢谢！

Answer 1

当你没有设置它存储null因此你需要初始化它先试试mapTextView = findViewById(R.id.mapTextView); 主要活动示例

    public class MainActivity extends AppCompatActivity {
        public final static String EXTRA_MESSAGE = "com.example.myfirstapp.MESSAGE";
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
        }

        /** Called when the user clicks the Send button */
        public void sendMessage(View view) {
            Intent intent = new Intent(this, DisplayMessageActivity.class);
            EditText editText = (EditText) findViewById(R.id.edit_message);
            String message = editText.getText().toString();
            intent.putExtra(EXTRA_MESSAGE, message);
            startActivity(intent);
        }
    }

Now second activity you want to switch

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

       Intent intent = getIntent();
       String message = intent.getStringExtra(MainActivity.EXTRA_MESSAGE);
       TextView textView = new TextView(this);
       textView.setTextSize(40);
       textView.setText(message);

       ViewGroup layout = (ViewGroup) findViewById(R.id.activity_display_message);
       layout.addView(textView);
    }

Answer 2

你无法调用屏幕上不存在的视图!!

但是，如果您的SecondActivity正在运行。您可以使用界面或EventBus库连接到TextView。

Answer 3

setContentView(R.layout.activity_main);

正如您在MainActivity中所做的那样，现在您只能参考activity_main中的所有对象。

现在为了实现您想要的功能，（获取 second_activity.xml 中的textview参考），您必须使用布局充气器来扩充second_activity.xml然后，您可以在MainActivity中执行和处理 OnClick 任务。

LayoutInflater inflater = LayoutInflater.from(this);
View layout= inflater.inflate(R.layout.second_activity.xml, null, false);
TextView text = (TextView)layout.findViewById(R.id.mapTextView);
text.setOnClickListener(this);

您还可以在 activity_main.xml 中加入 second_activity.xml ，以实现您的功能。

如何从其他布局调用链接TextView

3 个答案: