一个总是返回 null 的方法 [重复]

Question

decibelChart.postDelayed(new Runnable() {
                        @Override
                        public void run() {
                            int chartValue;
                            decibelChart.setNoDataText("Drawing Decibel Chart Error !");
                            decibelChart.setDragEnabled(false);
                            decibelChart.setScaleEnabled(false);
                            decibelChart.setDrawGridBackground(false);
                            decibelChart.setPinchZoom(false);
                            decibelChart.setBackgroundColor(Color.TRANSPARENT);
                            decibelChart.setData(lineData);

                            if (mediaRecorderForDB != null) {
                                chartValue = mediaRecorderForDB.getMaxAmplitude();
                            } else if (mediaRecorder != null) {
                                chartValue = mediaRecorder.getMaxAmplitude();
                            } else
                                chartValue = 0;

                            LineData myData = decibelChart.getData();

                            if (myData != null) {
                                ILineDataSet set = myData.getDataSetByIndex(0);

                                if (set == null){
                                    LineDataSet dataSet = new LineDataSet(null,"Dynamic");
                                    dataSet.setAxisDependency(YAxis.AxisDependency.LEFT);
                                    dataSet.setLineWidth(3f);
                                    dataSet.setColor(Color.WHITE);
                                    dataSet.setMode(LineDataSet.Mode.CUBIC_BEZIER);
                                    dataSet.setCubicIntensity(1f);
                                    myData.addDataSet(dataSet);
                                }

                                myData.addEntry(new Entry(set.getEntryCount(), chartValue + 5), 0);
                                myData.notifyDataChanged();
                                decibelChart.setMaxVisibleValueCount(150);
                                decibelChart.moveViewToX(myData.getEntryCount());
                            }

                            Log.e("[CHART_ERROR]", "CHART DRAWING");

                        }
                    },250);

set.getEntryCount() 返回 null 并抛出异常。我怎样才能克服它？我尝试了很多东西，但无法实现。 这些值来自麦克风，它们是分贝值。我想为这些值绘制折线图。

Answer 1

让我们逐行回顾一下

if (myData != null) {  //here you ask if myData is NOT null
    ILineDataSet set = myData.getDataSetByIndex(0);
    if (set == null){ // here you ask if set IS null 
        LineDataSet dataSet = new LineDataSet(null,"Dynamic"); //If set IS null you create the dataset
        //....
        myData.addDataSet(dataSet);
    }
    myData.addEntry(new Entry(set.getEntryCount(), chartValue + 5), 0); //what happens if set is still null? It will thow exception
}

一个可能的解决方案是

if (myData != null) {  //here you ask if myData is NOT null
    ILineDataSet set = myData.getDataSetByIndex(0);
    if (set == null){ // here you ask if set IS null 
        LineDataSet dataSet = new LineDataSet(null,"Dynamic"); //If set IS null you create the dataset
        //....
        myData.addDataSet(dataSet);
        myData.addEntry(new Entry(dataSet.getEntryCount(), chartValue + 5), 0); //here we are sure dataSet is not null because you created it
    } else { // this means set is NOT null
        myData.addEntry(new Entry(set.getEntryCount(), chartValue + 5), 0); //here we are sure set is not null because it is the ELSE for the IS NULL question
    }
    myData.notifyDataChanged();
    decibelChart.setMaxVisibleValueCount(150);
    decibelChart.moveViewToX(myData.getEntryCount());
}

编码愉快！