Question

嗨，所以我对编程很陌生。所以我正在处理的应用程序是一个用数组填充的listView。我添加了一个监听器，这样当从列表中选择一个项目时，它就会打开一个新的活动。现在，新活动的内容基于选择的项目。我可以通过选择列表项来启动新活动。但是当我尝试设置新活动的textview时，应用程序停止运行。我查看了很多相关帖子，但仍无法弄清楚如何设置文字。

继承我的MainActivity.java

    package com.example.zach.listview;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.TextView;
import  android.widget.Toast;
import static com.example.zach.listview.R.id.routeDetailsView;

public class MainActivity extends AppCompatActivity {

public static String[] routes = {"Information","Crag Map","Main Wall","1. Shark Bait - 5.9", "2. Rain Check - 5.8", "3. Rain Check Direct - 5.7+",
        "4. Arocknophobia - 5.7", "5. Balls Deep - 5.9+", "6. Jingle Bells - 5.9", "7. Itching to Climb - 5.8-", "8. Hog Nose 5.10+",
        "9. Slab Dance - 5.10", "10. Don't Screw with My Disco - 5.11c"};

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

    //TextView for route details
    final TextView routeDetailsView = (TextView) findViewById(R.id.routeDetailsView);

    ListAdapter routeAdapter = new CustomAdapter(this, routes);
    final ListView routeListView = (ListView) findViewById(R.id.routeListView);
    routeListView.setAdapter(routeAdapter);



    routeListView.setOnItemClickListener(
            new AdapterView.OnItemClickListener() {
                @Override
                public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                    String route = String.valueOf(parent.getItemAtPosition(position));

                    if (route == "1. Shark Bait - 5.9") {
                        Intent routeDetails = new Intent(view.getContext(), RouteDetails.class);
                        startActivity(routeDetails);
                        routeDetailsView.setText("Shark Bait - 5.9");

                    }

                }

            }


    );


  }
}

Heres My activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.zach.listview.MainActivity">


<ListView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_alignParentTop="true"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true"
    android:layout_marginTop="24dp"
    android:id="@+id/routeListView" />
</RelativeLayout>

继承我的RouteDetails.java

package com.example.zach.listview;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.TextView;
import static com.example.zach.listview.MainActivity.routes;

public class RouteDetails extends AppCompatActivity {

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

    //TextView for route details
   final TextView routeDetailsView = (TextView)findViewById(R.id.routeDetailsView);



    //if(route == "1. Shark Bait - 5.9"){
    //routeDetailsView.setText("Shark Bait - 5.9");
//}


}
}

和我的activity_route_details.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_route_details"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.zach.listview.RouteDetails">

<TextView
    android:text="TextView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="14dp"
    android:id="@+id/routeDetailsView" />
 </RelativeLayout>

我真的很感激任何帮助！

编辑：这里是我的customAdapter.java

package com.example.zach.listview;

import android.content.Context;
import android.support.annotation.MainThread;
import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.TextView;
import  android.widget.Toast;
import com.example.zach.listview.MainActivity;

/**
* Created by Zach on 11/3/2016.
*/

class CustomAdapter extends ArrayAdapter<String>{

public CustomAdapter(Context context, String[] routes) {
    super(context, R.layout.custom_row ,routes);
}

@NonNull
@Override
public View getView(int position, View convertView, ViewGroup parent) {

    LayoutInflater routeInflater = LayoutInflater.from(getContext());
    View customView = convertView;
    if(customView == null){customView =     routeInflater.inflate(R.layout.custom_row, parent, false);}

    String singleRoute = getItem(position);
    TextView routeText = (TextView) customView.findViewById(R.id.routeText);

    //for adding count numbers to listView
    //int pos = position+1;
    //routeText.setText(+pos + ". " +  MainActivity.routes [position]);
    //pos++;

    routeText.setText(singleRoute);
    return customView;
}
}

和我的错误消息

E/AndroidRuntime: FATAL EXCEPTION: main
              Process: com.example.zach.listview, PID: 3137
              java.lang.NullPointerException: Attempt to invoke virtual    method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
                  at com.example.zach.listview.MainActivity$1.onItemClick(MainActivity.java:51)
                  at android.widget.AdapterView.performItemClick(AdapterView.java:310)
                  at android.widget.AbsListView.performItemClick(AbsListView.java:1155)
                  at  android.widget.AbsListView$PerformClick.run(AbsListView.java:3126)
                  at android.widget.AbsListView$3.run(AbsListView.java:4041)
                  at android.os.Handler.handleCallback(Handler.java:751)
                  at android.os.Handler.dispatchMessage(Handler.java:95)
                  at android.os.Looper.loop(Looper.java:154)
                  at android.app.ActivityThread.main(ActivityThread.java:6077)
                  at java.lang.reflect.Method.invoke(Native Method)
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)

申请已终止。

Answer 1

您必须在意向活动之间发送数据：
发送：

        Intent routeDetails = new Intent(view.getContext(), RouteDetails.class);
        routeDetails.putExtra("value","Shark Bait - 5.9");
        startActivity(routeDetails);

并在其他活动中获取数据：

        routeDetailsView.setText(getIntent().getExtras().getShort("value"))

App尝试设置textView时崩溃

1 个答案: