Question

我有一个arraylist这样做：

     ArrayList<Integer> id = new ArrayList<Integer>(); 
     for (int i = 0; i <= 20; i++) {
     id.add(getResources().getIdentifier("q"+i, "raw", getPackageName()));}

这种方法在稍微改变之前工作正常，但现在有力量关闭！我得到了这个logcat：

FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{yaAli.package313.hossein110/yaAli.package313.hossein110.know}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java)at android.app.ActivityThread.access$600(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java)
at android.os.Handler.dispatchMessage(Handler.java)
at android.os.Looper.loop(Looper.java)
at android.app.ActivityThread.main(ActivityThread.java)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at yaAli.package313.hossein110.know.onCreate(know.java:33)
at android.app.Activity.performCreate(Activity.java)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java)
... 12 more

这是我的OnCreate（）：

@Override
protected void onCreate(Bundle bundle) {
    super.onCreate(bundle);
    setContentView(R.layout.basetxt);        
    SharedPreferences   settings=PreferenceManager.getDefaultSharedPreferences(getBaseContext());
    ln=settings.getString("LASTREADln", null);
    if(ln.equals("-1")){ln="0";}
    if(ln!=null){
    final ScrollView s1=(ScrollView) findViewById(R.id.sV1);
    s1.post(new Runnable() {@Override
    public void run() {s1.scrollTo(0, Integer.valueOf(ln));} });}

    final MediaPlayer mp1=MediaPlayer.create(getBaseContext(), R.raw.arza);  

    String pos = getIntent().getStringExtra("key");
    String arr = getIntent().getStringExtra("list");


    TextView tvfa = (TextView)findViewById(R.id.TEXT313);

    String fontPath = "fonts/font1.ttf";
    String fontPath1 = "fonts/font2.ttf";

    Typeface tf = Typeface.createFromAsset(getAssets(), fontPath);
    Typeface tf1 = Typeface.createFromAsset(getAssets(), fontPath1);

    SharedPreferences sharedpreferences =    PreferenceManager.getDefaultSharedPreferences(getBaseContext());

    tvfa.getRootView().setKeepScreenOn(sharedpreferences.getBoolean("scrnon", false));
    String sizefa=   sharedpreferences.getString("fontsizefa",null);
    String colorfa=   sharedpreferences.getString("fontcolorfa",null);        
    boolean style=   sharedpreferences.getBoolean("appfont", false);
    boolean music=   sharedpreferences.getBoolean("musictype", false);
    boolean curr=   sharedpreferences.getBoolean("currputfont", false);

String t = read(file(pos,arr,null)); {

if (curr){tvfa.setText(PersianReshape.reshape(t));}else{tvfa.setText(t);} // Txt 
tvfa.setTextSize(1, Float.valueOf(sizefa).floatValue());                    // Size
tvfa.setTextColor(Color.parseColor(colorfa));                               // Color
if (style) { tvfa.setTypeface(tf1); }  else {tvfa.setTypeface(tf);}         // Type
if (music) { mp1.start(); } else { mp1.stop(); }  }}                          // Play
//----------------------------------------------------------------------------

Answer 1

java开发的最佳实践是让文字字符串执行.equals调用。所以代替：

var.equals("string")

你这样做：

"string".equals(var)

这可以保证在进行字符串比较时不会出现空指针异常。

此外，您似乎将数值存储为字符串。您没有将它们存储为整体的任何特殊原因？

Answer 2

可能在这里

ln=settings.getString("LASTREADln", null);

这应该是

ln=settings.getString("LASTREADln", "");

如果null设置为您的默认值，如果该密钥不存在或包含任何内容，那么如果它不包含任何内容，则应将其设置为＆＃34;＆＃34;，对于字符串比较，您应该查找!ln.contentsEquals("")而不是将其检查为null

对于从首选项文件中获得的所有字符串也是如此。将默认值设置为""而不是null

启动活动时出现NullpointerException

2 个答案: