首先，我必须说，我在开发方面是个新手，所以请原谅我的愚蠢问题。 我有两个活动。在MainActivity中，我有一个可以带我前往SecondActivity的按钮。触摸此按钮后，手机上出现黑屏。哪里有问题？如果您想告诉我一个问题，我将不胜感激。对不起我的英语不好。 这是代码：
清单：
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.ca_ltd.intenty">
<uses-permission android:name="android.permission.INTERNET"></uses-permission>
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity
android:name=".MainActivity"
android:label="@string/app_name"
android:theme="@style/AppTheme.NoActionBar">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".SecondActivity"></activity>
</application>
</manifest>
MainAcitivy：
public class MainActivity extends AppCompatActivity {
Button buttonNext; // to do intentu
Button buttonGo;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
createCustomDialog();
buttonNext = (Button) findViewById(R.id.buttonNext);
buttonNext.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent intent = new Intent(MainActivity.this,
SecondActivity.class);
startActivity(intent);
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
public void createCustomDialog(){
final Dialog dialog = new Dialog(this);
dialog.setContentView(R.layout.powitanie_test);
dialog.setTitle("Tets");
Button dalej = (Button) dialog.findViewById(R.id.buttonGo);
dalej.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
dialog.dismiss(); }
});
}
}
content_main：
<?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"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:context="com.example.ca_ltd.intenty.MainActivity"
tools:showIn="@layout/activity_main">
<Button
android:id="@+id/buttonNext"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Przejdź do następnego"
app:layout_constraintTop_toTopOf="parent"
android:layout_marginTop="8dp"
app:layout_constraintBottom_toBottomOf="parent"
android:layout_marginBottom="8dp"
android:layout_marginRight="8dp"
app:layout_constraintRight_toRightOf="parent"
android:layout_marginLeft="8dp"
app:layout_constraintLeft_toLeftOf="parent" />
</android.support.constraint.ConstraintLayout>
SecondActivity：
public class SecondActivity extends Activity {
ListView lv;
ArrayAdapter<String> adapter;
String address="http://10.0.0.2/soccer.php";
InputStream is=null;
String line=null;
String result=null;
String[] data;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_second);
lv=(ListView) findViewById(R.id.listView1);
StrictMode.setThreadPolicy((new StrictMode.ThreadPolicy.Builder().permitNetwork().build()));
getData();
adapter=new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, data);
lv.setAdapter(adapter);
}
private void getData()
{
try {
URL url = new URL(address);
HttpURLConnection con=(HttpURLConnection) url.openConnection();
con.setRequestMethod("GET");
is=new BufferedInputStream(con.getInputStream());
}catch (Exception e)
{
e.printStackTrace();
}
try
{
BufferedReader br=new BufferedReader(new InputStreamReader(is));
StringBuilder sb=new StringBuilder();
while((line=br.readLine()) != null);
{
sb.append(line+"\n");
}
is.close();
result=sb.toString();
}catch (Exception e)
{
e.printStackTrace();
}
try
{
JSONArray ja=new JSONArray(result);
JSONObject jo=null;
data=new String[ja.length()];
int i;
for (i = 0; i<ja.length();i++)
{
jo=ja.getJSONObject(i);
data[i]=jo.getString("Name");
}
}catch (Exception e)
{
e.printStackTrace();
}
}
}
activity_second：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<ListView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/listView1"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
></ListView>
</LinearLayout>
Logcat：
--------- beginning of crash
06-29 19:13:53.721 2831-2831/com.example.ca_ltd.intenty E/AndroidRuntime:
FATAL EXCEPTION: main
Process: com.example.ca_ltd.intenty, PID: 2831
java.lang.RuntimeException: Unable to start activity
ComponentInfo{com.example.ca_ltd.intenty/com.example.ca_ltd.intenty.SecondActivity}: java.lang.NullPointerException
at
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2817)
at
android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
at
android.app.ActivityThread.-wrap11(Unknown Source:0)
at
android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
at
android.os.Handler.dispatchMessage(Handler.java:105)
at
android.os.Looper.loop(Looper.java:164)
at
android.app.ActivityThread.main(ActivityThread.java:6541)
at
java.lang.reflect.Method.invoke(Native Method)
at
com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
Caused by: java.lang.NullPointerException
at
java.util.Objects.requireNonNull(Objects.java:203)
at
java.util.Arrays$ArrayList.<init>(Arrays.java:3741)
at
java.util.Arrays.asList(Arrays.java:3728)
at
android.widget.ArrayAdapter.<init>(ArrayAdapter.java:163)
at
com.example.ca_ltd.intenty.SecondActivity.onCreate(SecondActivity.java:44)
at
android.app.Activity.performCreate(Activity.java:6975)
at
android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1213)
at
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2770)
at
android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
at
android.app.ActivityThread.-wrap11(Unknown Source:0)
at
android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
at
android.os.Handler.dispatchMessage(Handler.java:105)
at
android.os.Looper.loop(Looper.java:164)
at
android.app.ActivityThread.main(ActivityThread.java:6541)
at
java.lang.reflect.Method.invoke(Native Method)
at
com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
答案 0 :(得分：0)
为什么要在主线程上进行网络调用。您的getData（）方法应在后台线程中执行，请使用asynctask或普通线程。此网络任务会消耗您的UI线程，这就是黑屏的原因，如果耗时超过5-6秒，则会导致ANR
以下是使用截击进行请求的示例
// Instantiate the RequestQueue.
RequestQueue queue = Volley.newRequestQueue(this);
String url ="http://www.google.com";
// Request a string response from the provided URL.
StringRequest stringRequest = new StringRequest(Request.Method.GET, url,
new Response.Listener<String>() {
@Override
public void onResponse(String response) {
// Parse your response here
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
// Error has occurred
}
});
// Add the request to the RequestQueue.
queue.add(stringRequest);
有关排球的更多信息，请访问此页面https://exceljet.net/formula/create-array-of-numbers
答案 1 :(得分：0)
您的应用程序崩溃是因为初始化适配器时，您的数据为空。解决此问题的第一步，您可以在获得api的结果并初始化data变量后创建适配器。