[英]I can't make my buttons work
我只是想開始在Android上制作Ap,我對C ++有點了解,但是我為了最簡單的事情而奮斗了幾天-我無法使按鈕正常工作。
我嘗試了所有教程方法,但我無法使按鈕成為聽眾-每次這樣做,我的程序都會崩潰。
代碼很簡單(我的方法下面沒有做任何更改),我也啟動了全新的Android Project,並像所有教程一樣對按鈕和TextView進行了編輯:
package com.example.buttonwork;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v7.app.ActionBarActivity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends ActionBarActivity {
Button but1;
TextView tv1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment())
.commit();
}
tv1 = (TextView) findViewById(R.id.tv1);
but1 = (Button) findViewById(R.id.b1);
but1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
tv1.setText("Button pressed");
}
});
}
@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;
}
@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();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
return rootView;
}
}
}
The LOGCAT:
04-26 15:51:39.435: W/dalvikvm(7185): threadid=1: thread exiting with uncaught exception (group=0x418762a0)
04-26 15:51:39.450: E/AndroidRuntime(7185): FATAL EXCEPTION: main
04-26 15:51:39.450: E/AndroidRuntime(7185): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.buttonwork/com.example.buttonwork.MainActivity}: java.lang.NullPointerException
04-26 15:51:39.450: E/AndroidRuntime(7185): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2110)
04-26 15:51:39.450: E/AndroidRuntime(7185): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2135)
04-26 15:51:39.450: E/AndroidRuntime(7185): at android.app.ActivityThread.access$700(ActivityThread.java:140)
04-26 15:51:39.450: E/AndroidRuntime(7185): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1237)
04-26 15:51:39.450: E/AndroidRuntime(7185): at android.os.Handler.dispatchMessage(Handler.java:99)
04-26 15:51:39.450: E/AndroidRuntime(7185): at android.os.Looper.loop(Looper.java:137)
04-26 15:51:39.450: E/AndroidRuntime(7185): at android.app.ActivityThread.main(ActivityThread.java:4921)
04-26 15:51:39.450: E/AndroidRuntime(7185): at java.lang.reflect.Method.invokeNative(Native Method)
04-26 15:51:39.450: E/AndroidRuntime(7185): at java.lang.reflect.Method.invoke(Method.java:511)
04-26 15:51:39.450: E/AndroidRuntime(7185): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1027)
04-26 15:51:39.450: E/AndroidRuntime(7185): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:794)
04-26 15:51:39.450: E/AndroidRuntime(7185): at dalvik.system.NativeStart.main(Native Method)
04-26 15:51:39.450: E/AndroidRuntime(7185): Caused by: java.lang.NullPointerException
04-26 15:51:39.450: E/AndroidRuntime(7185): at com.example.buttonwork.MainActivity.onCreate(MainActivity.java:29)
04-26 15:51:39.450: E/AndroidRuntime(7185): at android.app.Activity.performCreate(Activity.java:5206)
04-26 15:51:39.450: E/AndroidRuntime(7185): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094)
04-26 15:51:39.450: E/AndroidRuntime(7185): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2074)
04-26 15:51:39.450: E/AndroidRuntime(7185): ... 11 more
程序每次崩潰。 我已經導入了所有內容,ID和名稱也都不錯。 請幫助我,因為現在我絕望了。 我只是想遍歷那些簡單的事情,並開始編寫一些確實有效並可以輸出的東西,但是我陷入了這樣一個簡單的步驟……
在這里,你去了 ..這就是你犯那個錯誤的地方 。 您正在嘗試在活動中獲取參考,而不是已定義的片段。
從onCreate()中 刪除按鈕,然后在占位符片段中添加這些組件。 這就是您獲得空指針的原因。
注意:使用getActivity()在片段中引用您的組件。
在片段中,您必須像這樣進行更改:
public static class PlaceholderFragment extends Fragment {
public PlaceholderFragment (){}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
return rootView;
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onActivityCreated(savedInstanceState);
Button but1 = (Button)getActivity(). findViewById(R.id.b1);
TextView tv1 = (TextView)getActivity(). findViewById(R.id.tv1);
but1.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
tv1.setText("Button pressed");
}
});
}
}
希望這可以幫助.. :)
使用此方法並從onCreate(Bundle savedInstanceState)
方法中刪除tb1
和bt1
初始化代碼
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
tv1 = (TextView) (rootView.findViewById(R.id.tv1));
but1 = (Button) (rootView.findViewById(R.id.b1));
but1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
tv1.setText("Button pressed");
}
});
return rootView;
}
}
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.