我有一个Listview。我想订购它，以便当新项目添加时，它们会添加到顶部。我试试
Collections.reverse(ListElementsArrayList);
它有效。但在（第二次，第三次点击，....）之后它混合了所有早期的项目。这是可能的。如果有，请帮助我。
我的主要活动
package com.pradeep.ap;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.graphics.Color;
import android.os.Build;
import android.os.Handler;
import android.support.annotation.RequiresApi;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.BaseAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.RelativeLayout;
import android.widget.Toast;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
public class AP extends AppCompatActivity {
EditText A, B, D, N, AN;
Button a, b, d, n, an, AP, GP, HP;
int Count = 0;
ListView LV;
String[] ListElements = new String[]{};
List<String> ListElementsArrayList;
ArrayAdapter<String> adapter;
Handler handler;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_ap);
A = (EditText) findViewById(R.id.eta);
B = (EditText) findViewById(R.id.etb);
D = (EditText) findViewById(R.id.etd);
N = (EditText) findViewById(R.id.etn);
AN = (EditText) findViewById(R.id.etan);
AP = (Button) findViewById(R.id.apap);
GP = (Button) findViewById(R.id.apgp);
HP = (Button) findViewById(R.id.aphp);
a = (Button) findViewById(R.id.a);
b = (Button) findViewById(R.id.b);
d = (Button) findViewById(R.id.d);
n = (Button) findViewById(R.id.n);
an = (Button) findViewById(R.id.an);
LV = (ListView) findViewById(R.id.lv);
handler = new Handler();
ListElementsArrayList = new ArrayList<String>(Arrays.asList(ListElements));
adapter = new ArrayAdapter<String>(AP.this,android.R.layout.simple_list_item_1,
ListElementsArrayList);
LV.setAdapter(adapter);
adapter.notifyDataSetChanged();
a.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
float numb = 0;
float numd = 0;
float numleal=0;
float result = 0;
int Result;
if (TextUtils.isEmpty(B.getText().toString())
|| TextUtils.isEmpty(D.getText().toString())) {
return;
}
numb = Float.parseFloat(B.getText().toString());
numd = Float.parseFloat(D.getText().toString());
ListElementsArrayList.add(" First term of AP is = " + A.getText().toString());
result = numb - numd;
Count = LV.getAdapter().getCount() + 1;
Result = (int) result;
A.setText("" + Result);
adapter.notifyDataSetChanged();
Collections.reverse(ListElementsArrayList);
}
});
b.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
float numa = 0;
float numd = 0;
float result = 0;
int Result;
Count = LV.getAdapter().getCount() + 1;
if (TextUtils.isEmpty(A.getText().toString())
|| TextUtils.isEmpty(D.getText().toString())) {
return;
}
numa = Float.parseFloat(A.getText().toString());
numd = Float.parseFloat(D.getText().toString());
result = numa + numd;
Result = (int) result;
B.setText("" + Result);
ListElementsArrayList.add(" Second term of AP is = " + B.getText().toString());
adapter.notifyDataSetChanged();
Collections.reverse(ListElementsArrayList);
}
});
d.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
float numa = 0;
float numb = 0;
float result = 0;
int Result;
if (TextUtils.isEmpty(A.getText().toString())
|| TextUtils.isEmpty(B.getText().toString())) {
return;
}
numa = Float.parseFloat(A.getText().toString());
numb = Float.parseFloat(B.getText().toString());
result = numb - numa;
Result = (int) result;
Count = LV.getAdapter().getCount() + 1;
D.setText("" + Result);
ListElementsArrayList.add(" Value of D is = " + D.getText().toString());
adapter.notifyDataSetChanged();
Collections.reverse(ListElementsArrayList);
}
});
n.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
float numa = 0;
float numd = 0;
float numan = 0;
float result = 0;
int Result;
if (TextUtils.isEmpty(A.getText().toString())
|| TextUtils.isEmpty(D.getText().toString())
|| TextUtils.isEmpty(AN.getText().toString())) {
return;
}
numa = Float.parseFloat(A.getText().toString());
numd = Float.parseFloat(D.getText().toString());
numan = Float.parseFloat(AN.getText().toString());
result = ((numan - numa) / numd) + 1;
Result = (int) result;
Count = LV.getAdapter().getCount() + 1;
N.setText("" + Result);
ListElementsArrayList.add(" Number of term/terms in this AP is = " + N.getText().toString());
adapter.notifyDataSetChanged();
Collections.reverse(ListElementsArrayList);
}
});
an.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
float numa = 0;
float numd = 0;
float numn = 0;
float result = 0;
int Result;
if (TextUtils.isEmpty(A.getText().toString())
|| TextUtils.isEmpty(D.getText().toString())
|| TextUtils.isEmpty(N.getText().toString())) {
return;
}
numa = Float.parseFloat(A.getText().toString());
numd = Float.parseFloat(D.getText().toString());
numn = Float.parseFloat(N.getText().toString());
result = ((numn - 1) * numd) + numa;
Result = (int) result;
AN.setText("" + Result);
Count = LV.getAdapter().getCount() + 1;
ListElementsArrayList.add(" Term/Terms of this AP is = " + AN.getText().toString());
adapter.notifyDataSetChanged();
adapter.getCount();
Collections.reverse(ListElementsArrayList);
}
});
}
}