当我尝试从主要 Activity 启动第二个 Activity 时，我不断收到 nullpointerexception 错误，我的主要 Activity 代码如下: 包 com.cep.daredevil;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.LinearLayout;
import android.widget.Toast;
public class MainActivity extends Activity {
public boolean filled = true;
EditText taskArray[] = new EditText[200];
EditText descArray[] = new EditText[200];
String taskArr[] = new String[200];
String descArr[] = new String[200];
int taskId[] = new int[200];
int descId[] = new int[200];
int n=0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
LinearLayout llayout = (LinearLayout)findViewById(R.id.llayout);
Button addfield = new Button(this);
addfield.setText("+");
llayout.addView(addfield);
addfield.setOnClickListener(new Button.OnClickListener()
{
public void onClick(View v)
{
addtask();
}
});
for(int i=0;i<3;i++)
{
addtask();
}
LinearLayout blayout = (LinearLayout)findViewById(R.id.blayout);
Button submit = new Button(this);
submit.setText("Enter Dare");
Button viewdare = new Button(this);
viewdare.setText("View Dares");
blayout.addView(submit);
blayout.addView(viewdare);
submit.setOnClickListener(new Button.OnClickListener()
{
public void onClick(View v)
{
inputdare(null);
}
});
viewdare.setOnClickListener(new Button.OnClickListener()
{
public void onClick(View v)
{
listdare();
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
public void addtask()
{
LinearLayout llayout = (LinearLayout)findViewById(R.id.llayout);
taskArray[n] = new EditText(this);
taskArray[n].setHint("Task Title");
taskArray[n].setId(n+10000000);
taskArray[n].setPadding(26,30,25,8);
descArray[n] = new EditText(this);
descArray[n].setHint("Task Description");
descArray[n].setId(n+20000000);
llayout.addView(taskArray[n]);
llayout.addView(descArray[n]);
n++;
}
public void inputdare(View v){
EditText daretitle = (EditText)findViewById(R.id.title);
String dare = daretitle.getText().toString();
for (int i=0;i<n;i++)
{
if (taskArr[i] != null)
{
taskArr[i] = taskArray[i].getText().toString();
}
Integer id = taskArray[i].getId();
if (id != null)
{
taskId[i] = id;
}
}
Intent intent = new Intent(this, DisplayDares.class);
Bundle bundle = new Bundle();
bundle.putStringArray("TASKS", taskArr);
bundle.putIntArray("TASKID", taskId);
bundle.putBoolean("INPUT", true);
intent.putExtras(bundle);
startActivity(intent);
}
}
public void listdare()
{
Intent intent = new Intent(this, DisplayDares.class);
Bundle bundle = new Bundle();
bundle.putBoolean("INPUT", false);
intent.putExtras(bundle);
startActivity(intent);
}
}
似乎导致问题的函数是在我的第二个 Activity 中，在这里:
package com.cep.daredevil;
import android.app.Activity;
import android.os.Bundle;
import android.support.v4.app.NavUtils;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.LinearLayout;
import android.widget.TextView;
public class DisplayDares extends Activity {
public final static String PREFS = "Preferences";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.display_dare);
setupActionBar();
Bundle bundle = getIntent().getExtras();
Boolean input = bundle.getBoolean("INPUT");
if (input == false){}
else
{
int[] taskId = bundle.getIntArray("TASKID");
final String[] taskArray = bundle.getStringArray("TASKS");
LinearLayout layout = (LinearLayout)findViewById(R.id.layout);
TextView test = (TextView)findViewById(taskId[0]);
test.setText(taskArray[1]);
layout.addView(test);
}
}
}
我得到的错误是这样的:
03-08 13:32:18.053: E/AndroidRuntime(6873): FATAL EXCEPTION: main
03-08 13:32:18.053: E/AndroidRuntime(6873): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.cep.daredevil/com.cep.daredevil.DisplayDares}: java.lang.NullPointerException
03-08 13:32:18.053: E/AndroidRuntime(6873): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
03-08 13:32:18.053: E/AndroidRuntime(6873): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
03-08 13:32:18.053: E/AndroidRuntime(6873): at android.app.ActivityThread.access$600(ActivityThread.java:141)
03-08 13:32:18.053: E/AndroidRuntime(6873): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
03-08 13:32:18.053: E/AndroidRuntime(6873): at android.os.Handler.dispatchMessage(Handler.java:99)
03-08 13:32:18.053: E/AndroidRuntime(6873): at android.os.Looper.loop(Looper.java:137)
03-08 13:32:18.053: E/AndroidRuntime(6873): at android.app.ActivityThread.main(ActivityThread.java:5041)
03-08 13:32:18.053: E/AndroidRuntime(6873): at java.lang.reflect.Method.invokeNative(Native Method)
03-08 13:32:18.053: E/AndroidRuntime(6873): at java.lang.reflect.Method.invoke(Method.java:511)
03-08 13:32:18.053: E/AndroidRuntime(6873): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
03-08 13:32:18.053: E/AndroidRuntime(6873): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
03-08 13:32:18.053: E/AndroidRuntime(6873): at dalvik.system.NativeStart.main(Native Method)
03-08 13:32:18.053: E/AndroidRuntime(6873): Caused by: java.lang.NullPointerException
03-08 13:32:18.053: E/AndroidRuntime(6873): at com.cep.daredevil.DisplayDares.onCreate(DisplayDares.java:32)
03-08 13:32:18.053: E/AndroidRuntime(6873): at android.app.Activity.performCreate(Activity.java:5104)
03-08 13:32:18.053: E/AndroidRuntime(6873): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
03-08 13:32:18.053: E/AndroidRuntime(6873): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
最佳答案
传递代码后，第 34 行似乎是:
layout.addView(test);
因此这一行会生成空指针异常
检查你的布局id是否相同。
提示:
在错误堆栈跟踪中，您可以进一步查看导致错误的原因:
03-08 13:32:18.053: E/AndroidRuntime(6873): Caused by: java.lang.NullPointerException
03-08 13:32:18.053: E/AndroidRuntime(6873): at com.cep.daredevil.DisplayDares.onCreate(DisplayDares.java:34)
DisplayDares.java:34
表示 DisplayDares.java 文件中的第 34 行。
您将看到以下行:
layout.addView(test);
现在 test 不能为 NULL，因为它不会抛出该错误。所以布局必须是。
关于java - nullpointerException 无法启动 Activity ，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/15295273/