的Android TextView的與空指針異常

Question

的Android TextView的與空指針異常

失敗，其在「disp.setText（」 0「）不失敗;」

裏面的方法「保護無效的onCreate（捆綁savedInstanceState）{」

我想大多數的網提供的建議。仍然無法解決它。

請需要幫助....

我的佈局： 「fragment_main.xml」

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:tools="http://schemas.android.com/tools" 
android:layout_width="match_parent" 
android:layout_height="match_parent" 
android:onClick="num_Clicked" 
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.ullas.Test1.MainActivity$PlaceholderFragment" > 

<TextView 
    android:id="@+id/textView1" 
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
     android:layout_alignParentTop="true" 
     android:layout_centerHorizontal="true" 
     android:layout_marginTop="17dp" 
     android:gravity="right" 
     android:text="Large Text" 
     android:textAppearance="?android:attr/textAppearanceLarge" /> 
</RelativeLayout> 

和我的活動是： 「MainActivity.java」

import android.support.v7.app.ActionBarActivity; 
import android.support.v4.app.Fragment; 
import android.os.Bundle; 
import android.view.LayoutInflater; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.*; 

public class MainActivity extends ActionBarActivity { 
    TextView disp; 

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

     disp = (TextView)findViewById(R.id.textView1); 
     disp.setText("0"); 


     if (savedInstanceState == null) { 
      getSupportFragmentManager().beginTransaction().add(R.id.container, new PlaceholderFragment()).commit(); 
     } 
    } 

Answer 1

視圖textView1在加載的佈局文件中找不到。在從佈局獲取視圖之前應該創建視圖層次結構。

Answer 2

你告訴你的佈局是「fragment_main.xml」，textview是在這個XML中。

在你的代碼

，要設置不同的佈局XML：

setContentView(R.layout.activity_main); 
disp = (TextView)findViewById(R.id.textView1); 

你必須設置你想使用的佈局，爲了能夠達到你的TextView：

setContentView(R.layout.fragment_main); 
disp = (TextView)findViewById(R.id.textView1); 

Answer 3

完成 「MainActivity.java」 低於

---

package com.example.test; 

import android.app.Activity; 
import android.app.ActionBar; 
import android.app.Fragment; 
import android.os.Bundle; 
import android.view.LayoutInflater; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.TextView; 
import android.os.Build; 

public class MainActivity extends Activity { 

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

     TextView disp; 
     disp = (TextView) findViewById(R.id.textView1); 
     disp.setText("0"); 

     if (savedInstanceState == null) { 
      getFragmentManager().beginTransaction() 
        .add(R.id.container, new PlaceholderFragment()).commit(); 
     } 
    } 

    @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; 
     } 
    } 

} 

---

和下面是完整的 「fragment_main.xml」

---

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:tools="http://schemas.android.com/tools" 
    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.test.MainActivity$PlaceholderFragment" > 

    <TextView 
     android:id="@+id/textView1" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:layout_alignParentLeft="true" 
     android:layout_alignParentRight="true" 
     android:layout_alignParentTop="true" 
     android:layout_marginTop="30dp" 
     android:gravity="right" 
     android:text="Large Text" 
     android:textAppearance="?android:attr/textAppearanceLarge" /> 

</RelativeLayout> 

---

下面是 「activity_main.xml中」

---

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:tools="http://schemas.android.com/tools" 
    android:id="@+id/container" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    tools:context="com.example.test.MainActivity" 
    tools:ignore="MergeRootFrame" /> 

---

和還有一件事，當我通過默認創建一個新項目時，它會給我這個「Fragment_main.xml」