Question

当我点击按钮显示ProgressDialog

时，我遇到了这个错误

03-08 14:29:00.169 8564-8564/com.mohammedmoaayed.test2 E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.mohammedmoaayed.test2, PID: 8564
Theme: themes:{}
java.lang.IllegalStateException: Could not execute method for android:onClick
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:293)
at android.view.View.performClick(View.java:5204)
at android.view.View$PerformClick.run(View.java:21158)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5471)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Method.invoke(Native Method)
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)
at android.view.View.performClick(View.java:5204) 
at android.view.View$PerformClick.run(View.java:21158) 
at android.os.Handler.handleCallback(Handler.java:739) 
at android.os.Handler.dispatchMessage(Handler.java:95) 
at android.os.Looper.loop(Looper.java:148) 
at android.app.ActivityThread.main(ActivityThread.java:5471) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ProgressDialog.setTitle(java.lang.CharSequence)' on a null object reference
at com.mohammedmoaayed.test2.MainActivity.buclick(MainActivity.java:26)
at java.lang.reflect.Method.invoke(Native Method) 
at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288) 
at android.view.View.performClick(View.java:5204) 
at android.view.View$PerformClick.run(View.java:21158) 
at android.os.Handler.handleCallback(Handler.java:739) 
at android.os.Handler.dispatchMessage(Handler.java:95) 
at android.os.Looper.loop(Looper.java:148) 
at android.app.ActivityThread.main(ActivityThread.java:5471) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

这是我的java代码

package com.mohammedmoaayed.test2;

import android.app.Activity;
import android.app.ProgressDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;

public class MainActivity extends AppCompatActivity {
Activity myac;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    myac=this;
}

mythread t1;
ProgressDialog bardown;

public void buclick(View view) {

    bardown.setTitle("Downloaing ");
    bardown.setMessage("Download is >>>>");
    bardown.setProgressStyle(bardown.STYLE_HORIZONTAL);
    bardown.setProgress(0);
    bardown.setMax(20);
    bardown.show();
    t1 = new mythread();
    t1.start();

}

class mythread extends Thread {
    public void run (){
    while (bardown.getProgress()<20) {
        myac.runOnUiThread(new Runnable() {
            @Override
            public void run() {
                bardown.incrementProgressBy(1);
            }

        });

        try {
            Thread.sleep(1000);
        } catch (Exception ex) {}
    }
        myac.runOnUiThread(new Runnable() {
            @Override
            public void run() {
                bardown.dismiss();
            }
        });
    }

}

}

xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout    
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.mohammedmoaayed.test2.MainActivity">


<Button
    android:id="@+id/button2"
    android:layout_width="395dp"
    android:layout_height="587dp"
    android:onClick="buclick"
    android:text="Button"
    tools:layout_editor_absoluteX="8dp"
    tools:layout_editor_absoluteY="8dp" />

Answer 1

你在null对象上调用A。你必须首先实例化它;

setTitle()

或者如果您动态创建它，请使用此

bardown = (ProgressBar)findViewById(R.id.bardown);

Answer 2

您没有对ProgressDialog进行初始化，因此请初始化ProgressDialog“bardown”

在活动中初始化

bardown = new ProgressDialog(this);// write this line

在片段中初始化

bardown = new ProgressDialog(getActivity());// write this line

例如。

 public void buclick(View view) {

    bardown = new ProgressDialog(this);// write this line
    bardown.setTitle("Downloaing ");
    bardown.setMessage("Download is >>>>");
    bardown.setProgressStyle(bardown.STYLE_HORIZONTAL);
    bardown.setProgress(0);
    bardown.setMax(20);
    bardown.show();
    t1 = new mythread();
    t1.start();

}

Answer 3

您尚未初始化ProgressDialog。在使用之前初始化它。在调用setTitle方法之前添加以下行。

bardown = new ProgressDialog(MainActivity.this);

Answer 4

使用此

初始化对话框

ProgressDialog dialog = new ProgressDialog(Activity_Map_Advance_Tracking.this);dialog.setMessage("Loading....");
        dialog.show();

android的执行方法：onClick

4 个答案: