android.widget.ProgressBar中没有默认的构造函数可用

Question

首先我是Android的初学者。 我想创建一个类来处理进度条并设置一些动画动作。 不幸的是， 系统显示标题中提到的错误。 这是我的代码：

import android.graphics.Canvas; 
import android.widget.ProgressBar; 

public class TexPtrogressBar extends ProgressBar { 
    @Override 
    protected synchronized void onDraw(Canvas canvas) { 
     super.onDraw(canvas); 
    } 
} 

在第三行发生错误。 有什么不对？感谢

Answer 1

必须覆盖3层的构造是这样的：

public TexPtrogressBar(Context context, AttributeSet attrs, int defStyle) { 
     super(context, attrs, defStyle); 
    } 

    public TexPtrogressBar(Context context, AttributeSet attrs) { 
     super(context, attrs); 
    } 

    public TexPtrogressBar(Context context) { 
     super(context); 
    } 

Answer 2

从ProgressBar类代码，如果你继承它，你必须提供的，至少构造

public ProgressBar(Context context, AttributeSet attrs) { 
    this(context, attrs, com.android.internal.R.attr.progressBarStyle); 
} 

public ProgressBar(Context context, AttributeSet attrs, int defStyleAttr) { 
    this(context, attrs, defStyleAttr, 0); 
} 

public ProgressBar(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) { 
    super(context, attrs, defStyleAttr, defStyleRes); 

    mUiThreadId = Thread.currentThread().getId(); 
    initProgressBar(); 

    final TypedArray a = context.obtainStyledAttributes(
      attrs, R.styleable.ProgressBar, defStyleAttr, defStyleRes); 

    mNoInvalidate = true; 

    final Drawable progressDrawable = a.getDrawable(R.styleable.ProgressBar_progressDrawable); 
    if (progressDrawable != null) { 
     // Calling this method can set mMaxHeight, make sure the corresponding 
     // XML attribute for mMaxHeight is read after calling this method 
     setProgressDrawableTiled(progressDrawable); 
    } 


    mDuration = a.getInt(R.styleable.ProgressBar_indeterminateDuration, mDuration); 

    mMinWidth = a.getDimensionPixelSize(R.styleable.ProgressBar_minWidth, mMinWidth); 
    mMaxWidth = a.getDimensionPixelSize(R.styleable.ProgressBar_maxWidth, mMaxWidth); 
    mMinHeight = a.getDimensionPixelSize(R.styleable.ProgressBar_minHeight, mMinHeight); 
    mMaxHeight = a.getDimensionPixelSize(R.styleable.ProgressBar_maxHeight, mMaxHeight); 

    mBehavior = a.getInt(R.styleable.ProgressBar_indeterminateBehavior, mBehavior); 

    final int resID = a.getResourceId(
      com.android.internal.R.styleable.ProgressBar_interpolator, 
      android.R.anim.linear_interpolator); // default to linear interpolator 
    if (resID > 0) { 
     setInterpolator(context, resID); 
    } 

    setMax(a.getInt(R.styleable.ProgressBar_max, mMax)); 

    setProgress(a.getInt(R.styleable.ProgressBar_progress, mProgress)); 

    setSecondaryProgress(
      a.getInt(R.styleable.ProgressBar_secondaryProgress, mSecondaryProgress)); 

    final Drawable indeterminateDrawable = a.getDrawable(
      R.styleable.ProgressBar_indeterminateDrawable); 
    if (indeterminateDrawable != null) { 
     setIndeterminateDrawableTiled(indeterminateDrawable); 
    } 

    mOnlyIndeterminate = a.getBoolean(
      R.styleable.ProgressBar_indeterminateOnly, mOnlyIndeterminate); 

    mNoInvalidate = false; 

    setIndeterminate(mOnlyIndeterminate || a.getBoolean(
      R.styleable.ProgressBar_indeterminate, mIndeterminate)); 

    mMirrorForRtl = a.getBoolean(R.styleable.ProgressBar_mirrorForRtl, mMirrorForRtl); 

    if (a.hasValue(R.styleable.ProgressBar_progressTintMode)) { 
     if (mProgressTintInfo == null) { 
      mProgressTintInfo = new ProgressTintInfo(); 
     } 
     mProgressTintInfo.mProgressTintMode = Drawable.parseTintMode(a.getInt(
       R.styleable.ProgressBar_progressBackgroundTintMode, -1), null); 
     mProgressTintInfo.mHasProgressTintMode = true; 
    } 

    if (a.hasValue(R.styleable.ProgressBar_progressTint)) { 
     if (mProgressTintInfo == null) { 
      mProgressTintInfo = new ProgressTintInfo(); 
     } 
     mProgressTintInfo.mProgressTintList = a.getColorStateList(
       R.styleable.ProgressBar_progressTint); 
     mProgressTintInfo.mHasProgressTint = true; 
    } 

    if (a.hasValue(R.styleable.ProgressBar_progressBackgroundTintMode)) { 
     if (mProgressTintInfo == null) { 
      mProgressTintInfo = new ProgressTintInfo(); 
     } 
     mProgressTintInfo.mProgressBackgroundTintMode = Drawable.parseTintMode(a.getInt(
       R.styleable.ProgressBar_progressTintMode, -1), null); 
     mProgressTintInfo.mHasProgressBackgroundTintMode = true; 
    } 

    if (a.hasValue(R.styleable.ProgressBar_progressBackgroundTint)) { 
     if (mProgressTintInfo == null) { 
      mProgressTintInfo = new ProgressTintInfo(); 
     } 
     mProgressTintInfo.mProgressBackgroundTintList = a.getColorStateList(
       R.styleable.ProgressBar_progressBackgroundTint); 
     mProgressTintInfo.mHasProgressBackgroundTint = true; 
    } 

    if (a.hasValue(R.styleable.ProgressBar_secondaryProgressTintMode)) { 
     if (mProgressTintInfo == null) { 
      mProgressTintInfo = new ProgressTintInfo(); 
     } 
     mProgressTintInfo.mSecondaryProgressTintMode = Drawable.parseTintMode(
       a.getInt(R.styleable.ProgressBar_secondaryProgressTintMode, -1), null); 
     mProgressTintInfo.mHasSecondaryProgressTintMode = true; 
    } 

    if (a.hasValue(R.styleable.ProgressBar_secondaryProgressTint)) { 
     if (mProgressTintInfo == null) { 
      mProgressTintInfo = new ProgressTintInfo(); 
     } 
     mProgressTintInfo.mSecondaryProgressTintList = a.getColorStateList(
       R.styleable.ProgressBar_secondaryProgressTint); 
     mProgressTintInfo.mHasSecondaryProgressTint = true; 
    } 

    if (a.hasValue(R.styleable.ProgressBar_indeterminateTint)) { 
     if (mProgressTintInfo == null) { 
      mProgressTintInfo = new ProgressTintInfo(); 
     } 
     mProgressTintInfo.mIndeterminateTintMode = Drawable.parseTintMode(a.getInt(
       R.styleable.ProgressBar_indeterminateTintMode, -1), null); 
     mProgressTintInfo.mHasIndeterminateTintMode = true; 
    } 

    if (a.hasValue(R.styleable.ProgressBar_indeterminateTint)) { 
     if (mProgressTintInfo == null) { 
      mProgressTintInfo = new ProgressTintInfo(); 
     } 
     mProgressTintInfo.mIndeterminateTintList = a.getColorStateList(
       R.styleable.ProgressBar_indeterminateTint); 
     mProgressTintInfo.mHasIndeterminateTint = true; 
    } 

    a.recycle(); 

    applyProgressTints(); 
    applyIndeterminateTint(); 

    // If not explicitly specified this view is important for accessibility. 
    if (getImportantForAccessibility() == View.IMPORTANT_FOR_ACCESSIBILITY_AUTO) { 
     setImportantForAccessibility(View.IMPORTANT_FOR_ACCESSIBILITY_YES); 
    } 
} 

参考之一到official document

Answer 3

您的等级

public class TexPtrogressBar extends ProgressBar { 
    @Override 
    protected synchronized void onDraw(Canvas canvas) { 
     super.onDraw(canvas); 
    } 
} 

有一个隐含的默认构造函数，看起来编译器像

public TexPtrogressBar() { 
    super(); // Looking for ProgressBar(); 
} 

但是，ProgressBar没有与签名的构造。您需要添加一个调用ProgressBar定义的构造函数的构造函数。

您的构造函数不必具有与ProgressBar的构造函数相同的参数，但它需要调用ProgressBar的构造函数之一。